Merge branch 'preview' into listing-tweaks

145 files changed, 8497 insertions, 2779 deletions

diff --git a/src/content/dependencies/generateAlbumCommentaryPage.js b/src/content/dependencies/generateAlbumCommentaryPage.js
index de619251..3ad1549e 100644
--- a/src/content/dependencies/generateAlbumCommentaryPage.js
+++ b/src/content/dependencies/generateAlbumCommentaryPage.js
@@ -2,10 +2,13 @@ import {stitchArrays} from '#sugar';
 
 export default {
   contentDependencies: [
+    'generateAlbumCoverArtwork',
     'generateAlbumNavAccent',
+    'generateAlbumSidebarTrackSection',
     'generateAlbumStyleRules',
     'generateColorStyleVariables',
     'generateContentHeading',
+    'generateTrackCoverArtwork',
     'generatePageLayout',
     'linkAlbum',
     'linkTrack',
@@ -21,7 +24,7 @@ export default {
       relation('generatePageLayout');
 
     relations.albumStyleRules =
-      relation('generateAlbumStyleRules', album);
+      relation('generateAlbumStyleRules', album, null);
 
     relations.albumLink =
       relation('linkAlbum', album);
@@ -30,6 +33,11 @@ export default {
       relation('generateAlbumNavAccent', album, null);
 
     if (album.commentary) {
+      if (album.hasCoverArt) {
+        relations.albumCommentaryCover =
+          relation('generateAlbumCoverArtwork', album);
+      }
+
       relations.albumCommentaryContent =
         relation('transformContent', album.commentary);
     }
@@ -46,6 +54,13 @@ export default {
       tracksWithCommentary
         .map(track => relation('linkTrack', track));
 
+    relations.trackCommentaryCovers =
+      tracksWithCommentary
+        .map(track =>
+          (track.hasUniqueCoverArt
+            ? relation('generateTrackCoverArtwork', track)
+            : null));
+
     relations.trackCommentaryContent =
       tracksWithCommentary
         .map(track => relation('transformContent', track.commentary));
@@ -57,6 +72,13 @@ export default {
             ? null
             : relation('generateColorStyleVariables')));
 
+    relations.sidebarAlbumLink =
+      relation('linkAlbum', album);
+
+    relations.sidebarTrackSections =
+      album.trackSections.map(trackSection =>
+        relation('generateAlbumSidebarTrackSection', album, null, trackSection));
+
     return relations;
   },
 
@@ -129,6 +151,9 @@ export default {
               {class: ['content-heading']},
               language.$('albumCommentaryPage.entry.title.albumCommentary')),
 
+            relations.albumCommentaryCover
+              ?.slots({mode: 'commentary'}),
+
             html.tag('blockquote',
               relations.albumCommentaryContent),
           ],
@@ -137,15 +162,19 @@ export default {
             heading: relations.trackCommentaryHeadings,
             link: relations.trackCommentaryLinks,
             directory: data.trackCommentaryDirectories,
+            cover: relations.trackCommentaryCovers,
             content: relations.trackCommentaryContent,
             colorVariables: relations.trackCommentaryColorVariables,
             color: data.trackCommentaryColors,
-          }).map(({heading, link, directory, content, colorVariables, color}) => [
+          }).map(({heading, link, directory, cover, content, colorVariables, color}) => [
               heading.slots({
                 tag: 'h3',
                 id: directory,
                 title: link,
               }),
+
+              cover?.slots({mode: 'commentary'}),
+
               html.tag('blockquote',
                 (color
                   ? {style: colorVariables.slot('color', color).content}
@@ -170,6 +199,17 @@ export default {
               }),
           },
         ],
+
+        leftSidebarStickyMode: 'column',
+        leftSidebarContent: [
+          html.tag('h1', relations.sidebarAlbumLink),
+          relations.sidebarTrackSections.map(section =>
+            section.slots({
+              anchor: true,
+              open: true,
+              mode: 'commentary',
+            })),
+        ],
       });
   },
 };
diff --git a/src/content/dependencies/generateAlbumGalleryNoTrackArtworksLine.js b/src/content/dependencies/generateAlbumGalleryNoTrackArtworksLine.js
new file mode 100644
index 00000000..ad99cb87
--- /dev/null
+++ b/src/content/dependencies/generateAlbumGalleryNoTrackArtworksLine.js
@@ -0,0 +1,7 @@
+export default {
+  extraDependencies: ['html', 'language'],
+
+  generate: ({html, language}) =>
+    html.tag('p', {class: 'quick-info'},
+      language.$('albumGalleryPage.noTrackArtworksLine')),
+};
diff --git a/src/content/dependencies/generateAlbumGalleryPage.js b/src/content/dependencies/generateAlbumGalleryPage.js
index 68b56bd9..f61b1983 100644
--- a/src/content/dependencies/generateAlbumGalleryPage.js
+++ b/src/content/dependencies/generateAlbumGalleryPage.js
@@ -3,8 +3,10 @@ import {compareArrays, stitchArrays} from '#sugar';
 export default {
   contentDependencies: [
     'generateAlbumGalleryCoverArtistsLine',
+    'generateAlbumGalleryNoTrackArtworksLine',
     'generateAlbumGalleryStatsLine',
     'generateAlbumNavAccent',
+    'generateAlbumSecondaryNav',
     'generateAlbumStyleRules',
     'generateCoverGrid',
     'generatePageLayout',
@@ -51,7 +53,7 @@ export default {
       relation('generatePageLayout');
 
     relations.albumStyleRules =
-      relation('generateAlbumStyleRules', album);
+      relation('generateAlbumStyleRules', album, null);
 
     relations.albumLink =
       relation('linkAlbum', album);
@@ -59,9 +61,17 @@ export default {
     relations.albumNavAccent =
       relation('generateAlbumNavAccent', album, null);
 
+    relations.secondaryNav =
+      relation('generateAlbumSecondaryNav', album);
+
     relations.statsLine =
       relation('generateAlbumGalleryStatsLine', album);
 
+    if (album.tracks.every(track => !track.hasUniqueCoverArt)) {
+      relations.noTrackArtworksLine =
+        relation('generateAlbumGalleryNoTrackArtworksLine');
+    }
+
     if (query.coverArtistsForAllTracks) {
       relations.coverArtistsLine =
         relation('generateAlbumGalleryCoverArtistsLine', query.coverArtistsForAllTracks);
@@ -70,15 +80,25 @@ export default {
     relations.coverGrid =
       relation('generateCoverGrid');
 
-    relations.links =
-      album.tracks.map(track =>
-        relation('linkTrack', track));
+    relations.links = [
+      relation('linkAlbum', album),
 
-    relations.images =
-      album.tracks.map(track =>
-        (track.hasUniqueCoverArt
-          ? relation('image', track.artTags)
-          : relation('image')));
+      ...
+        album.tracks
+          .map(track => relation('linkTrack', track)),
+    ];
+
+    relations.images = [
+      (album.hasCoverArt
+        ? relation('image', album.artTags)
+        : relation('image')),
+
+      ...
+        album.tracks.map(track =>
+          (track.hasUniqueCoverArt
+            ? relation('image', track.artTags)
+            : relation('image'))),
+    ];
 
     return relations;
   },
@@ -89,27 +109,41 @@ export default {
     data.name = album.name;
     data.color = album.color;
 
-    data.names =
-      album.tracks.map(track => track.name);
+    data.names = [
+      album.name,
+      ...album.tracks.map(track => track.name),
+    ];
 
-    data.coverArtists =
-      album.tracks.map(track => {
-        if (query.coverArtistsForAllTracks) {
-          return null;
-        }
+    data.coverArtists = [
+      (album.hasCoverArt
+        ? album.coverArtistContribs.map(({who: artist}) => artist.name)
+        : null),
 
-        if (track.hasUniqueCoverArt) {
-          return track.coverArtistContribs.map(({who: artist}) => artist.name);
-        }
+      ...
+        album.tracks.map(track => {
+          if (query.coverArtistsForAllTracks) {
+            return null;
+          }
 
-        return null;
-      });
+          if (track.hasUniqueCoverArt) {
+            return track.coverArtistContribs.map(({who: artist}) => artist.name);
+          }
+
+          return null;
+        }),
+    ];
 
-    data.paths =
-      album.tracks.map(track =>
-        (track.hasUniqueCoverArt
-          ? ['media.trackCover', track.album.directory, track.directory, track.coverArtFileExtension]
-          : null));
+    data.paths = [
+      (album.hasCoverArt
+        ? ['media.albumCover', album.directory, album.coverArtFileExtension]
+        : null),
+
+      ...
+        album.tracks.map(track =>
+          (track.hasUniqueCoverArt
+            ? ['media.trackCover', track.album.directory, track.directory, track.coverArtFileExtension]
+            : null)),
+    ];
 
     return data;
   },
@@ -131,6 +165,7 @@ export default {
         mainContent: [
           relations.statsLine,
           relations.coverArtistsLine,
+          relations.noTrackArtworksLine,
 
           relations.coverGrid
             .slots({
@@ -172,6 +207,8 @@ export default {
               }),
           },
         ],
+
+        secondaryNav: relations.secondaryNav,
       });
   },
 };
diff --git a/src/content/dependencies/generateAlbumInfoPage.js b/src/content/dependencies/generateAlbumInfoPage.js
index ce17ab21..5fe27caf 100644
--- a/src/content/dependencies/generateAlbumInfoPage.js
+++ b/src/content/dependencies/generateAlbumInfoPage.js
@@ -37,14 +37,14 @@ export default {
       relation('generatePageLayout');
 
     relations.albumStyleRules =
-      relation('generateAlbumStyleRules', album);
+      relation('generateAlbumStyleRules', album, null);
 
     relations.socialEmbed =
       relation('generateAlbumSocialEmbed', album);
 
     relations.coverArtistChronologyContributions =
       getChronologyRelations(album, {
-        contributions: album.coverArtistContribs,
+        contributions: album.coverArtistContribs ?? [],
 
         linkArtist: artist => relation('linkArtist', artist),
 
diff --git a/src/content/dependencies/generateAlbumNavAccent.js b/src/content/dependencies/generateAlbumNavAccent.js
index c79219bb..7eb1dac0 100644
--- a/src/content/dependencies/generateAlbumNavAccent.js
+++ b/src/content/dependencies/generateAlbumNavAccent.js
@@ -33,10 +33,8 @@ export default {
       }
     }
 
-    if (album.tracks.some(t => t.hasUniqueCoverArt)) {
-      relations.albumGalleryLink =
-        relation('linkAlbumGallery', album);
-    }
+    relations.albumGalleryLink =
+      relation('linkAlbumGallery', album);
 
     if (album.commentary || album.tracks.some(t => t.commentary)) {
       relations.albumCommentaryLink =
@@ -49,6 +47,7 @@ export default {
   data(album, track) {
     return {
       hasMultipleTracks: album.tracks.length > 1,
+      galleryIsStub: album.tracks.every(t => !t.hasUniqueCoverArt),
       isTrackPage: !!track,
     };
   },
@@ -66,10 +65,11 @@ export default {
     const {content: extraLinks = []} =
       slots.showExtraLinks &&
         {content: [
-          relations.albumGalleryLink?.slots({
-            attributes: {class: slots.currentExtra === 'gallery' && 'current'},
-            content: language.$('albumPage.nav.gallery'),
-          }),
+          (!data.galleryIsStub || slots.currentExtra === 'gallery') &&
+            relations.albumGalleryLink?.slots({
+              attributes: {class: slots.currentExtra === 'gallery' && 'current'},
+              content: language.$('albumPage.nav.gallery'),
+            }),
 
           relations.albumCommentaryLink?.slots({
             attributes: {class: slots.currentExtra === 'commentary' && 'current'},
diff --git a/src/content/dependencies/generateAlbumSecondaryNav.js b/src/content/dependencies/generateAlbumSecondaryNav.js
index 705dec51..8cf36fa4 100644
--- a/src/content/dependencies/generateAlbumSecondaryNav.js
+++ b/src/content/dependencies/generateAlbumSecondaryNav.js
@@ -5,7 +5,7 @@ export default {
     'generateColorStyleVariables',
     'generatePreviousNextLinks',
     'generateSecondaryNav',
-    'linkAlbum',
+    'linkAlbumDynamically',
     'linkGroup',
     'linkTrack',
   ],
@@ -64,14 +64,14 @@ export default {
         query.adjacentGroupInfo
           .map(({previousAlbum}) =>
             (previousAlbum
-              ? relation('linkAlbum', previousAlbum)
+              ? relation('linkAlbumDynamically', previousAlbum)
               : null));
 
       relations.nextAlbumLinks =
         query.adjacentGroupInfo
           .map(({nextAlbum}) =>
             (nextAlbum
-              ? relation('linkAlbum', nextAlbum)
+              ? relation('linkAlbumDynamically', nextAlbum)
               : null));
     }
 
diff --git a/src/content/dependencies/generateAlbumSidebarTrackSection.js b/src/content/dependencies/generateAlbumSidebarTrackSection.js
index 2aca6da1..d3cd37f0 100644
--- a/src/content/dependencies/generateAlbumSidebarTrackSection.js
+++ b/src/content/dependencies/generateAlbumSidebarTrackSection.js
@@ -33,10 +33,28 @@ export default {
       }
     }
 
+    data.trackDirectories =
+      trackSection.tracks
+        .map(track => track.directory);
+
+    data.tracksAreMissingCommentary =
+      trackSection.tracks
+        .map(track => !track.commentary);
+
     return data;
   },
 
-  generate(data, relations, {getColors, html, language}) {
+  slots: {
+    anchor: {type: 'boolean'},
+    open: {type: 'boolean'},
+
+    mode: {
+      validate: v => v.is('info', 'commentary'),
+      default: 'info',
+    },
+  },
+
+  generate(data, relations, slots, {getColors, html, language}) {
     const sectionName =
       html.tag('span', {class: 'group-name'},
         (data.isDefaultTrackSection
@@ -53,13 +71,28 @@ export default {
       relations.trackLinks.map((trackLink, index) =>
         html.tag('li',
           {
-            class:
+            class: [
               data.includesCurrentTrack &&
               index === data.currentTrackIndex &&
-              'current',
+                'current',
+
+              slots.mode === 'commentary' &&
+              data.tracksAreMissingCommentary[index] &&
+                'no-commentary',
+            ],
           },
           language.$('albumSidebar.trackList.item', {
-            track: trackLink,
+            track:
+              (slots.mode === 'commentary' && data.tracksAreMissingCommentary[index]
+                ? trackLink.slots({
+                    linkless: true,
+                  })
+             : slots.anchor
+                ? trackLink.slots({
+                    anchor: true,
+                    hash: data.trackDirectories[index],
+                  })
+                : trackLink),
           })));
 
     return html.tag('details',
@@ -67,6 +100,11 @@ export default {
         class: data.includesCurrentTrack && 'current',
 
         open: (
+          // Allow forcing open via a template slot.
+          // This isn't exactly janky, but the rest of this function
+          // kind of is when you contextualize it in a template...
+          slots.open ||
+
           // Leave sidebar track sections collapsed on album info page,
           // since there's already a view of the full track listing
           // in the main content area.
@@ -82,7 +120,7 @@ export default {
             (data.hasTrackNumbers
               ? language.$('albumSidebar.trackList.group.withRange', {
                   group: sectionName,
-                  range: `${data.firstTrackNumber}–${data.lastTrackNumber}`
+                  range: `${data.firstTrackNumber}–${data.lastTrackNumber}`
                 })
               : language.$('albumSidebar.trackList.group', {
                   group: sectionName,
diff --git a/src/content/dependencies/generateAlbumStyleRules.js b/src/content/dependencies/generateAlbumStyleRules.js
index 1acaea17..c5acf374 100644
--- a/src/content/dependencies/generateAlbumStyleRules.js
+++ b/src/content/dependencies/generateAlbumStyleRules.js
@@ -3,14 +3,13 @@ import {empty} from '#sugar';
 export default {
   extraDependencies: ['to'],
 
-  data(album) {
+  data(album, track) {
     const data = {};
 
     data.hasWallpaper = !empty(album.wallpaperArtistContribs);
     data.hasBanner = !empty(album.bannerArtistContribs);
 
     if (data.hasWallpaper) {
-      data.hasWallpaperStyle = !!album.wallpaperStyle;
       data.wallpaperPath = ['media.albumWallpaper', album.directory, album.wallpaperFileExtension];
       data.wallpaperStyle = album.wallpaperStyle;
     }
@@ -20,40 +19,54 @@ export default {
       data.bannerStyle = album.bannerStyle;
     }
 
+    data.albumDirectory = album.directory;
+
+    if (track) {
+      data.trackDirectory = track.directory;
+    }
+
     return data;
   },
 
   generate(data, {to}) {
-    const wallpaperPart =
-      (data.hasWallpaper
-        ? [
-            `body::before {`,
-            `    background-image: url("${to(...data.wallpaperPath)}");`,
-            ...(data.hasWallpaperStyle
-              ? data.wallpaperStyle
-                  .split('\n')
-                  .map(line => `    ${line}`)
-              : []),
-            `}`,
-          ]
-        : []);
+    const indent = parts =>
+      (parts ?? [])
+        .filter(Boolean)
+        .join('\n')
+        .split('\n')
+        .map(line => ' '.repeat(4) + line)
+        .join('\n');
 
-    const bannerPart =
-      (data.hasBannerStyle
-        ? [
-            `#banner img {`,
-            ...data.bannerStyle
-              .split('\n')
-              .map(line => `    ${line}`),
-            `}`,
-          ]
+    const rule = (selector, parts) =>
+      (!empty(parts.filter(Boolean))
+        ? [`${selector} {`, indent(parts), `}`]
         : []);
 
-    return [
-      ...wallpaperPart,
-      ...bannerPart,
-    ]
-      .filter(Boolean)
-      .join('\n');
+    const wallpaperRule =
+      data.hasWallpaper &&
+        rule(`body::before`, [
+          `background-image: url("${to(...data.wallpaperPath)}");`,
+          data.wallpaperStyle,
+        ]);
+
+    const bannerRule =
+      data.hasBanner &&
+        rule(`#banner img`, [
+          data.bannerStyle,
+        ]);
+
+    const dataRule =
+      rule(`:root`, [
+        data.albumDirectory &&
+          `--album-directory: ${data.albumDirectory};`,
+        data.trackDirectory &&
+          `--track-directory: ${data.trackDirectory};`,
+      ]);
+
+    return (
+      [wallpaperRule, bannerRule, dataRule]
+        .filter(Boolean)
+        .flat()
+        .join('\n'));
   },
 };
diff --git a/src/content/dependencies/generateAlbumTrackListItem.js b/src/content/dependencies/generateAlbumTrackListItem.js
index f65b47c9..f92712f9 100644
--- a/src/content/dependencies/generateAlbumTrackListItem.js
+++ b/src/content/dependencies/generateAlbumTrackListItem.js
@@ -1,4 +1,4 @@
-import {compareArrays} from '#sugar';
+import {compareArrays, empty} from '#sugar';
 
 export default {
   contentDependencies: [
@@ -11,9 +11,11 @@ export default {
   relations(relation, track) {
     const relations = {};
 
-    relations.contributionLinks =
-      track.artistContribs
-        .map(contrib => relation('linkContribution', contrib));
+    if (!empty(track.artistContribs)) {
+      relations.contributionLinks =
+        track.artistContribs
+          .map(contrib => relation('linkContribution', contrib));
+    }
 
     relations.trackLink =
       relation('linkTrack', track);
@@ -31,10 +33,12 @@ export default {
     }
 
     data.showArtists =
-      !compareArrays(
-        track.artistContribs.map(c => c.who),
-        album.artistContribs.map(c => c.who),
-        {checkOrder: false});
+      !empty(track.artistContribs) &&
+       (empty(album.artistContribs) ||
+        !compareArrays(
+          track.artistContribs.map(c => c.who),
+          album.artistContribs.map(c => c.who),
+          {checkOrder: false}));
 
     return data;
   },
diff --git a/src/content/dependencies/generateArtistInfoPageChunkItem.js b/src/content/dependencies/generateArtistInfoPageChunkItem.js
index 36f0ebcc..9f99513d 100644
--- a/src/content/dependencies/generateArtistInfoPageChunkItem.js
+++ b/src/content/dependencies/generateArtistInfoPageChunkItem.js
@@ -5,7 +5,7 @@ export default {
     content: {type: 'html'},
 
     otherArtistLinks: {validate: v => v.strictArrayOf(v.isHTML)},
-    contribution: {type: 'string'},
+    contribution: {type: 'html'},
     rerelease: {type: 'boolean'},
   },
 
@@ -30,7 +30,7 @@ export default {
         options.artists = language.formatConjunctionList(slots.otherArtistLinks);
       }
 
-      if (slots.contribution) {
+      if (!html.isBlank(slots.contribution)) {
         parts.push('withContribution');
         options.contribution = slots.contribution;
       }
diff --git a/src/content/dependencies/generateArtistInfoPageTracksChunkedList.js b/src/content/dependencies/generateArtistInfoPageTracksChunkedList.js
index 0566f713..654f759c 100644
--- a/src/content/dependencies/generateArtistInfoPageTracksChunkedList.js
+++ b/src/content/dependencies/generateArtistInfoPageTracksChunkedList.js
@@ -1,4 +1,4 @@
-import {accumulateSum, stitchArrays} from '#sugar';
+import {accumulateSum, empty, stitchArrays} from '#sugar';
 
 import {
   chunkByProperties,
@@ -16,7 +16,7 @@ export default {
     'linkTrack',
   ],
 
-  extraDependencies: ['language'],
+  extraDependencies: ['html', 'language'],
 
   query(artist) {
     const tracksAsArtistAndContributor =
@@ -122,11 +122,16 @@ export default {
 
       trackContributions:
         query.chunks.map(({chunk}) =>
-          chunk.map(({contribs}) =>
-            contribs
-              .filter(({who}) => who === artist)
-              .filter(({what}) => what)
-              .map(({what}) => what))),
+          chunk
+            .map(({contribs}) =>
+              contribs
+                .filter(({who}) => who === artist)
+                .filter(({what}) => what)
+                .map(({what}) => what))
+            .map(contributions =>
+              (empty(contributions)
+                ? null
+                : contributions))),
 
       trackRereleases:
         query.chunks.map(({chunk}) =>
@@ -134,7 +139,7 @@ export default {
     };
   },
 
-  generate(data, relations, {language}) {
+  generate(data, relations, {html, language}) {
     return relations.chunkedList.slots({
       chunks:
         stitchArrays({
@@ -192,7 +197,9 @@ export default {
                       rerelease,
 
                       contribution:
-                        language.formatUnitList(contribution),
+                        (contribution
+                          ? language.formatUnitList(contribution)
+                          : html.blank()),
 
                       content:
                         (duration
diff --git a/src/content/dependencies/generateCoverArtwork.js b/src/content/dependencies/generateCoverArtwork.js
index 4060c6b0..aeba97de 100644
--- a/src/content/dependencies/generateCoverArtwork.js
+++ b/src/content/dependencies/generateCoverArtwork.js
@@ -32,7 +32,7 @@ export default {
     },
 
     mode: {
-      validate: v => v.is('primary', 'thumbnail'),
+      validate: v => v.is('primary', 'thumbnail', 'commentary'),
       default: 'primary',
     },
   },
@@ -73,6 +73,19 @@ export default {
             square: true,
           });
 
+      case 'commentary':
+        return relations.image
+          .slots({
+            path: slots.path,
+            alt: slots.alt,
+            thumb: 'medium',
+            class: 'commentary-art',
+            reveal: true,
+            link: true,
+            square: true,
+            lazy: true,
+          });
+
       default:
         return html.blank();
     }
diff --git a/src/content/dependencies/generateCoverGrid.js b/src/content/dependencies/generateCoverGrid.js
index 9822e1ae..5636e4f3 100644
--- a/src/content/dependencies/generateCoverGrid.js
+++ b/src/content/dependencies/generateCoverGrid.js
@@ -2,7 +2,7 @@ import {stitchArrays} from '#sugar';
 
 export default {
   contentDependencies: ['generateGridActionLinks'],
-  extraDependencies: ['html'],
+  extraDependencies: ['html', 'language'],
 
   relations(relation) {
     return {
@@ -20,7 +20,7 @@ export default {
     actionLinks: {validate: v => v.sparseArrayOf(v.isHTML)},
   },
 
-  generate(relations, slots, {html}) {
+  generate(relations, slots, {html, language}) {
     return (
       html.tag('div', {class: 'grid-listing'}, [
         stitchArrays({
@@ -42,8 +42,12 @@ export default {
                       ? slots.lazy
                       : false),
                 }),
-                html.tag('span', {[html.onlyIfContent]: true}, name),
-                html.tag('span', {[html.onlyIfContent]: true}, info),
+
+                html.tag('span', {[html.onlyIfContent]: true},
+                  language.sanitize(name)),
+
+                html.tag('span', {[html.onlyIfContent]: true},
+                  language.sanitize(info)),
               ],
             })),
 
diff --git a/src/content/dependencies/generateFlashActGalleryPage.js b/src/content/dependencies/generateFlashActGalleryPage.js
new file mode 100644
index 00000000..8eea58bb
--- /dev/null
+++ b/src/content/dependencies/generateFlashActGalleryPage.js
@@ -0,0 +1,91 @@
+import {stitchArrays} from '#sugar';
+
+export default {
+  contentDependencies: [
+    'generateCoverGrid',
+    'generateFlashActNavAccent',
+    'generateFlashActSidebar',
+    'generatePageLayout',
+    'image',
+    'linkFlash',
+    'linkFlashIndex',
+  ],
+
+  extraDependencies: ['html', 'language'],
+
+  relations: (relation, act) => ({
+    layout:
+      relation('generatePageLayout'),
+
+    flashIndexLink:
+      relation('linkFlashIndex'),
+
+    flashActNavAccent:
+      relation('generateFlashActNavAccent', act),
+
+    sidebar:
+      relation('generateFlashActSidebar', act, null),
+
+    coverGrid:
+      relation('generateCoverGrid'),
+
+    coverGridImages:
+      act.flashes
+        .map(_flash => relation('image')),
+
+    flashLinks:
+      act.flashes
+        .map(flash => relation('linkFlash', flash)),
+  }),
+
+  data: (act) => ({
+    name: act.name,
+    color: act.color,
+
+    flashNames:
+      act.flashes.map(flash => flash.name),
+
+    flashCoverPaths:
+      act.flashes.map(flash =>
+        ['media.flashArt', flash.directory, flash.coverArtFileExtension])
+  }),
+
+  generate(data, relations, {html, language}) {
+    return relations.layout.slots({
+      title:
+        language.$('flashPage.title', {
+          flash: new html.Tag(null, null, data.name),
+        }),
+
+      color: data.color,
+      headingMode: 'static',
+
+      mainClasses: ['flash-index'],
+      mainContent: [
+        relations.coverGrid.slots({
+          links: relations.flashLinks,
+          names: data.flashNames,
+          lazy: 6,
+
+          images:
+            stitchArrays({
+              image: relations.coverGridImages,
+              path: data.flashCoverPaths,
+            }).map(({image, path}) =>
+                image.slot('path', path)),
+        }),
+      ],
+
+      navLinkStyle: 'hierarchical',
+      navLinks: [
+        {auto: 'home'},
+        {html: relations.flashIndexLink},
+        {auto: 'current'},
+      ],
+
+      navBottomRowContent: relations.flashActNavAccent,
+
+      ...relations.sidebar,
+    });
+  },
+};
diff --git a/src/content/dependencies/generateFlashActNavAccent.js b/src/content/dependencies/generateFlashActNavAccent.js
new file mode 100644
index 00000000..98504385
--- /dev/null
+++ b/src/content/dependencies/generateFlashActNavAccent.js
@@ -0,0 +1,74 @@
+import {empty} from '#sugar';
+
+export default {
+  contentDependencies: [
+    'generatePreviousNextLinks',
+    'linkFlashAct',
+  ],
+
+  extraDependencies: ['html', 'language', 'wikiData'],
+
+  sprawl({flashActData}) {
+    return {flashActData};
+  },
+
+  query(sprawl, flashAct) {
+    // Like with generateFlashNavAccent, don't sort chronologically here.
+    const flashActs =
+      sprawl.flashActData;
+
+    const index = flashActs.indexOf(flashAct);
+
+    const previousFlashAct =
+      (index > 0
+        ? flashActs[index - 1]
+        : null);
+
+    const nextFlashAct =
+      (index < flashActs.length - 1
+        ? flashActs[index + 1]
+        : null);
+
+    return {previousFlashAct, nextFlashAct};
+  },
+
+  relations(relation, query) {
+    const relations = {};
+
+    if (query.previousFlashAct || query.nextFlashAct) {
+      relations.previousNextLinks =
+        relation('generatePreviousNextLinks');
+
+      relations.previousFlashActLink =
+        (query.previousFlashAct
+          ? relation('linkFlashAct', query.previousFlashAct)
+          : null);
+
+      relations.nextFlashActLink =
+        (query.nextFlashAct
+          ? relation('linkFlashAct', query.nextFlashAct)
+          : null);
+    }
+
+    return relations;
+  },
+
+  generate(relations, {html, language}) {
+    const {content: previousNextLinks = []} =
+      relations.previousNextLinks &&
+        relations.previousNextLinks.slots({
+          previousLink: relations.previousFlashActLink,
+          nextLink: relations.nextFlashActLink,
+        });
+
+    const allLinks = [
+      ...previousNextLinks,
+    ].filter(Boolean);
+
+    if (empty(allLinks)) {
+      return html.blank();
+    }
+
+    return `(${language.formatUnitList(allLinks)})`;
+  },
+};
diff --git a/src/content/dependencies/generateFlashActSidebar.js b/src/content/dependencies/generateFlashActSidebar.js
new file mode 100644
index 00000000..bd6063c9
--- /dev/null
+++ b/src/content/dependencies/generateFlashActSidebar.js
@@ -0,0 +1,194 @@
+import find from '#find';
+import {stitchArrays} from '#sugar';
+
+export default {
+  contentDependencies: ['linkFlash', 'linkFlashAct', 'linkFlashIndex'],
+  extraDependencies: ['getColors', 'html', 'language', 'wikiData'],
+
+  // So help me Gog, the flash sidebar is heavily hard-coded.
+
+  sprawl: ({flashActData}) => ({flashActData}),
+
+  query(sprawl, act, flash) {
+    const findFlashAct = directory =>
+      find.flashAct(directory, sprawl.flashActData, {mode: 'error'});
+
+    const sideFirstActs = [
+      findFlashAct('flash-act:a1'),
+      findFlashAct('flash-act:a6a1'),
+      findFlashAct('flash-act:hiveswap'),
+      findFlashAct('flash-act:cool-and-new-web-comic'),
+      findFlashAct('flash-act:sunday-night-strifin'),
+    ];
+
+    const sideNames = [
+      `Side 1 (Acts 1-5)`,
+      `Side 2 (Acts 6-7)`,
+      `Additional Canon`,
+      `Fan Adventures`,
+      `Fan Games & More`,
+    ];
+
+    const sideColors = [
+      '#4ac925',
+      '#3796c6',
+      '#f2a400',
+      '#c466ff',
+      '#32c7fe',
+    ];
+
+    const sideFirstActIndexes =
+      sideFirstActs
+        .map(act => sprawl.flashActData.indexOf(act));
+
+    const actSideIndexes =
+      sprawl.flashActData
+        .map((act, actIndex) => actIndex)
+        .map(actIndex =>
+          sideFirstActIndexes
+            .findIndex((firstActIndex, i) =>
+              i === sideFirstActs.length - 1 ||
+                firstActIndex <= actIndex &&
+                sideFirstActIndexes[i + 1] > actIndex));
+
+    const sideActs =
+      sideNames
+        .map((name, sideIndex) =>
+          stitchArrays({
+            act: sprawl.flashActData,
+            actSideIndex: actSideIndexes,
+          }).filter(({actSideIndex}) => actSideIndex === sideIndex)
+            .map(({act}) => act));
+
+    const currentActFlashes =
+      act.flashes;
+
+    const currentFlashIndex =
+      currentActFlashes.indexOf(flash);
+
+    const currentSideIndex =
+      actSideIndexes[sprawl.flashActData.indexOf(act)];
+
+    const currentSideActs =
+      sideActs[currentSideIndex];
+
+    const currentActIndex =
+      currentSideActs.indexOf(act);
+
+    const fallbackListTerminology =
+      (currentSideIndex <= 1
+        ? 'flashesInThisAct'
+        : 'entriesInThisSection');
+
+    return {
+      sideNames,
+      sideColors,
+      sideActs,
+
+      currentSideIndex,
+      currentSideActs,
+      currentActIndex,
+      currentActFlashes,
+      currentFlashIndex,
+
+      fallbackListTerminology,
+    };
+  },
+
+  relations: (relation, query, sprawl, act, _flash) => ({
+    currentActLink:
+      relation('linkFlashAct', act),
+
+    flashIndexLink:
+      relation('linkFlashIndex'),
+
+    sideActLinks:
+      query.sideActs
+        .map(acts => acts
+          .map(act => relation('linkFlashAct', act))),
+
+    currentActFlashLinks:
+      act.flashes
+        .map(flash => relation('linkFlash', flash)),
+  }),
+
+  data: (query, sprawl, act, flash) => ({
+    isFlashActPage: !flash,
+
+    sideColors: query.sideColors,
+    sideNames: query.sideNames,
+
+    currentSideIndex: query.currentSideIndex,
+    currentActIndex: query.currentActIndex,
+    currentFlashIndex: query.currentFlashIndex,
+
+    customListTerminology: act.listTerminology,
+    fallbackListTerminology: query.fallbackListTerminology,
+  }),
+
+  generate(data, relations, {getColors, html, language}) {
+    const currentActBox = html.tags([
+      html.tag('h1', relations.currentActLink),
+
+      html.tag('details',
+        (data.isFlashActPage
+          ? {}
+          : {class: 'current', open: true}),
+        [
+          html.tag('summary',
+            html.tag('span', {class: 'group-name'},
+              (data.customListTerminology
+                ? language.sanitize(data.customListTerminology)
+                : language.$('flashSidebar.flashList', data.fallbackListTerminology)))),
+
+          html.tag('ul',
+            relations.currentActFlashLinks
+              .map((flashLink, index) =>
+                html.tag('li',
+                  {class: index === data.currentFlashIndex && 'current'},
+                  flashLink))),
+        ]),
+    ]);
+
+    const sideMapBox = html.tags([
+      html.tag('h1', relations.flashIndexLink),
+
+      stitchArrays({
+        sideName: data.sideNames,
+        sideColor: data.sideColors,
+        actLinks: relations.sideActLinks,
+      }).map(({sideName, sideColor, actLinks}, sideIndex) =>
+          html.tag('details', {
+            class: sideIndex === data.currentSideIndex && 'current',
+            open: data.isFlashActPage && sideIndex === data.currentSideIndex,
+            style: sideColor && `--primary-color: ${getColors(sideColor).primary}`
+          }, [
+            html.tag('summary',
+              html.tag('span', {class: 'group-name'},
+                sideName)),
+
+            html.tag('ul',
+              actLinks.map((actLink, actIndex) =>
+                html.tag('li',
+                  {class:
+                    sideIndex === data.currentSideIndex &&
+                    actIndex === data.currentActIndex &&
+                      'current'},
+                  actLink))),
+          ])),
+    ]);
+
+    return {
+      leftSidebarMultiple:
+        (data.isFlashActPage
+          ? [
+              {content: sideMapBox},
+              {content: currentActBox},
+            ]
+          : [
+              {content: currentActBox},
+              {content: sideMapBox},
+            ]),
+    };
+  },
+};
diff --git a/src/content/dependencies/generateFlashIndexPage.js b/src/content/dependencies/generateFlashIndexPage.js
index 66588fdb..ad1dab94 100644
--- a/src/content/dependencies/generateFlashIndexPage.js
+++ b/src/content/dependencies/generateFlashIndexPage.js
@@ -7,6 +7,7 @@ export default {
     'generatePageLayout',
     'image',
     'linkFlash',
+    'linkFlashAct',
   ],
 
   extraDependencies: ['html', 'language', 'wikiData'],
@@ -36,9 +37,9 @@ export default {
       query.flashActs
         .map(() => relation('generateColorStyleVariables')),
 
-    actFirstFlashLinks:
+    actLinks:
       query.flashActs
-        .map(act => relation('linkFlash', act.flashes[0])),
+        .map(act => relation('linkFlashAct', act)),
 
     actCoverGrids:
       query.flashActs
@@ -58,7 +59,7 @@ export default {
   data: (query) => ({
     jumpLinkAnchors:
       query.jumpActs
-        .map(act => act.anchor),
+        .map(act => act.directory),
 
     jumpLinkColors:
       query.jumpActs
@@ -70,16 +71,12 @@ export default {
 
     actAnchors:
       query.flashActs
-        .map(act => act.anchor),
+        .map(act => act.directory),
 
     actColors:
       query.flashActs
         .map(act => act.color),
 
-    actNames:
-      query.flashActs
-        .map(act => act.name),
-
     actCoverGridNames:
       query.flashActs
         .map(act => act.flashes
@@ -118,10 +115,9 @@ export default {
 
         stitchArrays({
           colorVariables: relations.actColorVariables,
-          firstFlashLink: relations.actFirstFlashLinks,
+          actLink: relations.actLinks,
           anchor: data.actAnchors,
           color: data.actColors,
-          name: data.actNames,
 
           coverGrid: relations.actCoverGrids,
           coverGridImages: relations.actCoverGridImages,
@@ -132,8 +128,7 @@ export default {
             colorVariables,
             anchor,
             color,
-            name,
-            firstFlashLink,
+            actLink,
 
             coverGrid,
             coverGridImages,
@@ -146,7 +141,7 @@ export default {
                 id: anchor,
                 style: colorVariables.slot('color', color).content,
               },
-              firstFlashLink.slot('content', name)),
+              actLink),
 
             coverGrid.slots({
               links: coverGridLinks,
diff --git a/src/content/dependencies/generateFlashInfoPage.js b/src/content/dependencies/generateFlashInfoPage.js
index 553d2f54..09c6b37c 100644
--- a/src/content/dependencies/generateFlashInfoPage.js
+++ b/src/content/dependencies/generateFlashInfoPage.js
@@ -4,13 +4,13 @@ export default {
   contentDependencies: [
     'generateContentHeading',
     'generateContributionList',
+    'generateFlashActSidebar',
     'generateFlashCoverArtwork',
     'generateFlashNavAccent',
-    'generateFlashSidebar',
     'generatePageLayout',
     'generateTrackList',
     'linkExternal',
-    'linkFlashIndex',
+    'linkFlashAct',
   ],
 
   extraDependencies: ['html', 'language'],
@@ -41,7 +41,7 @@ export default {
       relation('generatePageLayout');
 
     relations.sidebar =
-      relation('generateFlashSidebar', flash);
+      relation('generateFlashActSidebar', flash.act, flash);
 
     if (query.urls) {
       relations.externalLinks =
@@ -59,8 +59,8 @@ export default {
 
     const nav = sections.nav = {};
 
-    nav.flashIndexLink =
-      relation('linkFlashIndex');
+    nav.flashActLink =
+      relation('linkFlashAct', flash.act);
 
     nav.flashNavAccent =
       relation('generateFlashNavAccent', flash);
@@ -163,14 +163,11 @@ export default {
       navLinkStyle: 'hierarchical',
       navLinks: [
         {auto: 'home'},
-        {html: sec.nav.flashIndexLink},
+        {html: sec.nav.flashActLink.slot('color', false)},
         {auto: 'current'},
       ],
 
-      navBottomRowContent:
-        sec.nav.flashNavAccent.slots({
-          showFlashNavigation: true,
-        }),
+      navBottomRowContent: sec.nav.flashNavAccent,
 
       ...relations.sidebar,
     });
diff --git a/src/content/dependencies/generateFlashNavAccent.js b/src/content/dependencies/generateFlashNavAccent.js
index 2c8205d3..57196d06 100644
--- a/src/content/dependencies/generateFlashNavAccent.js
+++ b/src/content/dependencies/generateFlashNavAccent.js
@@ -55,13 +55,8 @@ export default {
     return relations;
   },
 
-  slots: {
-    showFlashNavigation: {type: 'boolean', default: false},
-  },
-
-  generate(relations, slots, {html, language}) {
+  generate(relations, {html, language}) {
     const {content: previousNextLinks = []} =
-      slots.showFlashNavigation &&
       relations.previousNextLinks &&
         relations.previousNextLinks.slots({
           previousLink: relations.previousFlashLink,
diff --git a/src/content/dependencies/generateFlashSidebar.js b/src/content/dependencies/generateFlashSidebar.js
deleted file mode 100644
index ba761922..00000000
--- a/src/content/dependencies/generateFlashSidebar.js
+++ /dev/null
@@ -1,236 +0,0 @@
-import {stitchArrays} from '#sugar';
-
-export default {
-  contentDependencies: ['linkFlash', 'linkFlashIndex'],
-  extraDependencies: ['html', 'wikiData'],
-
-  // So help me Gog, the flash sidebar is heavily hard-coded.
-
-  sprawl: ({flashActData}) => ({flashActData}),
-
-  query(sprawl, flash) {
-    const flashActs =
-      sprawl.flashActData.slice();
-
-    const act6 =
-      flashActs
-        .findIndex(act => act.name.startsWith('Act 6'));
-
-    const postCanon =
-      flashActs
-        .findIndex(act => act.name.includes('Post Canon'));
-
-    const outsideCanon =
-      postCanon +
-      flashActs
-        .slice(postCanon)
-        .findIndex(act => !act.name.includes('Post Canon'));
-
-    const currentAct = flash.act;
-
-    const actIndex =
-      flashActs
-        .indexOf(currentAct);
-
-    const side =
-      (actIndex < 0
-        ? 0
-     : actIndex < act6
-        ? 1
-     : actIndex < outsideCanon
-        ? 2
-        : 3);
-
-    const sideActs =
-      flashActs
-        .filter((act, index) =>
-          act.name.startsWith('Act 1') ||
-          act.name.startsWith('Act 6 Act 1') ||
-          act.name.startsWith('Hiveswap') ||
-          index >= outsideCanon);
-
-    const currentSideIndex =
-      sideActs
-        .findIndex(act => {
-          if (act.name.startsWith('Act 1')) {
-            return side === 1;
-          } else if (act.name.startsWith('Act 6 Act 1')) {
-            return side === 2;
-          } else if (act.name.startsWith('Hiveswap Act 1')) {
-            return side === 3;
-          } else {
-            return act === currentAct;
-          }
-        })
-
-    const sideNames =
-      sideActs
-        .map(act => {
-          if (act.name.startsWith('Act 1')) {
-            return `Side 1 (Acts 1-5)`;
-          } else if (act.name.startsWith('Act 6 Act 1')) {
-            return `Side 2 (Acts 6-7)`;
-          } else if (act.name.startsWith('Hiveswap Act 1')) {
-            return `Outside Canon (Misc. Games)`;
-          } else {
-            return act.name;
-          }
-        });
-
-    const sideColors =
-      sideActs
-        .map(act => {
-          if (act.name.startsWith('Act 1')) {
-            return '#4ac925';
-          } else if (act.name.startsWith('Act 6 Act 1')) {
-            return '#1076a2';
-          } else if (act.name.startsWith('Hiveswap Act 1')) {
-            return '#008282';
-          } else {
-            return act.color;
-          }
-        });
-
-    const sideFirstFlashes =
-      sideActs
-        .map(act => act.flashes[0]);
-
-    const scopeActs =
-      flashActs
-        .filter((act, index) => {
-          if (index < act6) {
-            return side === 1;
-          } else if (index < outsideCanon) {
-            return side === 2;
-          } else {
-            return false;
-          }
-        });
-
-    const currentScopeActIndex =
-      scopeActs.indexOf(currentAct);
-
-    const scopeActNames =
-      scopeActs
-        .map(act => act.name);
-
-    const scopeActFirstFlashes =
-      scopeActs
-        .map(act => act.flashes[0]);
-
-    const currentActFlashes =
-      currentAct.flashes;
-
-    const currentFlashIndex =
-      currentActFlashes
-        .indexOf(flash);
-
-    return {
-      currentSideIndex,
-      sideNames,
-      sideColors,
-      sideFirstFlashes,
-
-      currentScopeActIndex,
-      scopeActNames,
-      scopeActFirstFlashes,
-
-      currentActFlashes,
-      currentFlashIndex,
-    };
-  },
-
-  relations: (relation, query) => ({
-    flashIndexLink:
-      relation('linkFlashIndex'),
-
-    sideFirstFlashLinks:
-      query.sideFirstFlashes
-        .map(flash => relation('linkFlash', flash)),
-
-    scopeActFirstFlashLinks:
-      query.scopeActFirstFlashes
-        .map(flash => relation('linkFlash', flash)),
-
-    currentActFlashLinks:
-      query.currentActFlashes
-        .map(flash => relation('linkFlash', flash)),
-  }),
-
-  data: (query) => ({
-    currentSideIndex: query.currentSideIndex,
-    sideColors: query.sideColors,
-    sideNames: query.sideNames,
-
-    currentScopeActIndex: query.currentScopeActIndex,
-    scopeActNames: query.scopeActNames,
-
-    currentFlashIndex: query.currentFlashIndex,
-  }),
-
-  generate(data, relations, {html}) {
-    const currentActFlashList =
-      html.tag('ul',
-        relations.currentActFlashLinks
-          .map((flashLink, index) =>
-            html.tag('li',
-              {class: index === data.currentFlashIndex && 'current'},
-              flashLink)));
-
-    return {
-      leftSidebarContent: html.tags([
-        html.tag('h1', relations.flashIndexLink),
-
-        html.tag('dl',
-          stitchArrays({
-            sideFirstFlashLink: relations.sideFirstFlashLinks,
-            sideColor: data.sideColors,
-            sideName: data.sideNames,
-          }).map(({sideFirstFlashLink, sideColor, sideName}, index) => [
-              // Side acts are displayed whether part of Homestuck proper or
-              // not, and they're always the same regardless the current flash
-              // page. Scope acts, if applicable, and the list of flashes
-              // belonging to the current act, will be inserted after the
-              // heading of the current side.
-              html.tag('dt',
-                {class: [
-                  'side',
-                  index === data.currentSideIndex && 'current',
-                ]},
-                sideFirstFlashLink.slots({
-                  color: sideColor,
-                  content: sideName,
-                })),
-
-              // Scope acts are only applicable when inside Homestuck proper.
-              // Hiveswap and all acts beyond are each considered to be its
-              // own "side".
-              index === data.currentSideIndex &&
-              data.currentScopeActIndex !== -1 &&
-                stitchArrays({
-                  scopeActFirstFlashLink: relations.scopeActFirstFlashLinks,
-                  scopeActName: data.scopeActNames,
-                }).map(({scopeActFirstFlashLink, scopeActName}, index) => [
-                    html.tag('dt',
-                      {class: index === data.currentScopeActIndex && 'current'},
-                      scopeActFirstFlashLink.slot('content', scopeActName)),
-
-                    // Inside Homestuck proper, the flash list of the current
-                    // act should show after the heading for the relevant
-                    // scope act.
-                    index === data.currentScopeActIndex &&
-                      html.tag('dd', currentActFlashList),
-                  ]),
-
-              // Outside of Homestuck proper, the current act is represented
-              // by a side instead of a scope act, so place its flash list
-              // after the heading for the relevant side.
-              index === data.currentSideIndex &&
-              data.currentScopeActIndex === -1 &&
-                html.tag('dd', currentActFlashList),
-            ])),
-
-      ]),
-    };
-  },
-};
diff --git a/src/content/dependencies/generateFooterLocalizationLinks.js b/src/content/dependencies/generateFooterLocalizationLinks.js
index b4970b17..5df83566 100644
--- a/src/content/dependencies/generateFooterLocalizationLinks.js
+++ b/src/content/dependencies/generateFooterLocalizationLinks.js
@@ -38,7 +38,7 @@ export default {
 
     return html.tag('div', {class: 'footer-localization-links'},
       language.$('misc.uiLanguage', {
-        languages: links.join('\n'),
+        languages: language.formatListWithoutSeparator(links),
       }));
   },
 };
diff --git a/src/content/dependencies/generateGroupGalleryPage.js b/src/content/dependencies/generateGroupGalleryPage.js
index 47239f55..259f5dce 100644
--- a/src/content/dependencies/generateGroupGalleryPage.js
+++ b/src/content/dependencies/generateGroupGalleryPage.js
@@ -11,6 +11,7 @@ export default {
     'generateCoverCarousel',
     'generateCoverGrid',
     'generateGroupNavLinks',
+    'generateGroupSecondaryNav',
     'generateGroupSidebar',
     'generatePageLayout',
     'image',
@@ -20,18 +21,8 @@ export default {
 
   extraDependencies: ['html', 'language', 'wikiData'],
 
-  sprawl({listingSpec, wikiInfo}) {
-    const sprawl = {};
-    sprawl.enableGroupUI = wikiInfo.enableGroupUI;
-
-    if (wikiInfo.enableListings && wikiInfo.enableGroupUI) {
-      sprawl.groupsByCategoryListing =
-        listingSpec
-          .find(l => l.directory === 'groups/by-category');
-    }
-
-    return sprawl;
-  },
+  sprawl: ({wikiInfo}) =>
+    ({enableGroupUI: wikiInfo.enableGroupUI}),
 
   relations(relation, sprawl, group) {
     const relations = {};
@@ -46,15 +37,13 @@ export default {
       relation('generateGroupNavLinks', group);
 
     if (sprawl.enableGroupUI) {
+      relations.secondaryNav =
+        relation('generateGroupSecondaryNav', group);
+
       relations.sidebar =
         relation('generateGroupSidebar', group);
     }
 
-    if (sprawl.groupsByCategoryListing) {
-      relations.groupListingLink =
-        relation('linkListing', sprawl.groupsByCategoryListing);
-    }
-
     const carouselAlbums = filterItemsForCarousel(group.featuredAlbums);
 
     if (!empty(carouselAlbums)) {
@@ -160,15 +149,6 @@ export default {
                 })),
             })),
 
-          relations.groupListingLink &&
-            html.tag('p',
-              {class: 'quick-info'},
-              language.$('groupGalleryPage.anotherGroupLine', {
-                link:
-                  relations.groupListingLink
-                    .slot('content', language.$('groupGalleryPage.anotherGroupLine.link')),
-              })),
-
           relations.coverGrid
             .slots({
               links: relations.gridLinks,
@@ -208,6 +188,9 @@ export default {
           relations.navLinks
             .slot('currentExtra', 'gallery')
             .content,
+
+        secondaryNav:
+          relations.secondaryNav ?? null,
       });
   },
 };
diff --git a/src/content/dependencies/generateGroupInfoPage.js b/src/content/dependencies/generateGroupInfoPage.js
index e162a26a..0583755e 100644
--- a/src/content/dependencies/generateGroupInfoPage.js
+++ b/src/content/dependencies/generateGroupInfoPage.js
@@ -4,6 +4,7 @@ export default {
   contentDependencies: [
     'generateContentHeading',
     'generateGroupNavLinks',
+    'generateGroupSecondaryNav',
     'generateGroupSidebar',
     'generatePageLayout',
     'linkAlbum',
@@ -32,6 +33,9 @@ export default {
       relation('generateGroupNavLinks', group);
 
     if (sprawl.enableGroupUI) {
+      relations.secondaryNav =
+        relation('generateGroupSecondaryNav', group);
+
       relations.sidebar =
         relation('generateGroupSidebar', group);
     }
@@ -161,6 +165,8 @@ export default {
 
         navLinkStyle: 'hierarchical',
         navLinks: relations.navLinks.content,
+
+        secondaryNav: relations.secondaryNav ?? null,
       });
   },
 };
diff --git a/src/content/dependencies/generateGroupNavLinks.js b/src/content/dependencies/generateGroupNavLinks.js
index 68341e0a..5cde2ab4 100644
--- a/src/content/dependencies/generateGroupNavLinks.js
+++ b/src/content/dependencies/generateGroupNavLinks.js
@@ -2,10 +2,8 @@ import {empty} from '#sugar';
 
 export default {
   contentDependencies: [
-    'generatePreviousNextLinks',
     'linkGroup',
     'linkGroupGallery',
-    'linkGroupExtra',
   ],
 
   extraDependencies: ['html', 'language', 'wikiData'],
@@ -28,24 +26,6 @@ export default {
     relations.mainLink =
       relation('linkGroup', group);
 
-    relations.previousNextLinks =
-      relation('generatePreviousNextLinks');
-
-    const groups = sprawl.groupCategoryData
-      .flatMap(category => category.groups);
-
-    const index = groups.indexOf(group);
-
-    if (index > 0) {
-      relations.previousLink =
-        relation('linkGroupExtra', groups[index - 1]);
-    }
-
-    if (index < groups.length - 1) {
-      relations.nextLink =
-        relation('linkGroupExtra', groups[index + 1]);
-    }
-
     relations.infoLink =
       relation('linkGroup', group);
 
@@ -80,26 +60,6 @@ export default {
       ];
     }
 
-    const previousNextLinks =
-      (relations.previousLink || relations.nextLink) &&
-        relations.previousNextLinks.slots({
-          previousLink:
-            relations.previousLink
-              ?.slot('extra', slots.currentExtra)
-              ?.content
-            ?? null,
-          nextLink:
-            relations.nextLink
-              ?.slot('extra', slots.currentExtra)
-              ?.content
-            ?? null,
-        });
-
-    const previousNextPart =
-      previousNextLinks &&
-        language.formatUnitList(
-          previousNextLinks.content.filter(Boolean));
-
     const infoLink =
       relations.infoLink.slots({
         attributes: {class: slots.currentExtra === null && 'current'},
@@ -119,7 +79,9 @@ export default {
         : language.formatUnitList([infoLink, ...extraLinks]));
 
     const accent =
-      `(${[extrasPart, previousNextPart].filter(Boolean).join('; ')})`;
+      (extrasPart
+        ? `(${extrasPart})`
+        : null);
 
     return [
       {auto: 'home'},
diff --git a/src/content/dependencies/generateGroupSecondaryNav.js b/src/content/dependencies/generateGroupSecondaryNav.js
new file mode 100644
index 00000000..e3b28099
--- /dev/null
+++ b/src/content/dependencies/generateGroupSecondaryNav.js
@@ -0,0 +1,99 @@
+export default {
+  contentDependencies: [
+    'generateColorStyleVariables',
+    'generatePreviousNextLinks',
+    'generateSecondaryNav',
+    'linkGroupDynamically',
+    'linkListing',
+  ],
+
+  extraDependencies: ['html', 'language', 'wikiData'],
+
+  sprawl: ({listingSpec, wikiInfo}) => ({
+    groupsByCategoryListing:
+      (wikiInfo.enableListings
+        ? listingSpec
+            .find(l => l.directory === 'groups/by-category')
+        : null),
+  }),
+
+  query(sprawl, group) {
+    const groups = group.category.groups;
+    const index = groups.indexOf(group);
+
+    return {
+      previousGroup:
+        (index > 0
+          ? groups[index - 1]
+          : null),
+
+      nextGroup:
+        (index < groups.length - 1
+          ? groups[index + 1]
+          : null),
+    };
+  },
+
+  relations(relation, query, sprawl, _group) {
+    const relations = {};
+
+    relations.secondaryNav =
+      relation('generateSecondaryNav');
+
+    if (sprawl.groupsByCategoryListing) {
+      relations.categoryLink =
+        relation('linkListing', sprawl.groupsByCategoryListing);
+    }
+
+    relations.colorVariables =
+      relation('generateColorStyleVariables');
+
+    if (query.previousGroup || query.nextGroup) {
+      relations.previousNextLinks =
+        relation('generatePreviousNextLinks');
+    }
+
+    relations.previousGroupLink =
+      (query.previousGroup
+        ? relation('linkGroupDynamically', query.previousGroup)
+        : null);
+
+    relations.nextGroupLink =
+      (query.nextGroup
+        ? relation('linkGroupDynamically', query.nextGroup)
+        : null);
+
+    return relations;
+  },
+
+  data: (query, sprawl, group) => ({
+    categoryName: group.category.name,
+    categoryColor: group.category.color,
+  }),
+
+  generate(data, relations, {html, language}) {
+    const {content: previousNextPart} =
+      relations.previousNextLinks.slots({
+        previousLink: relations.previousGroupLink,
+        nextLink: relations.nextGroupLink,
+        id: true,
+      });
+
+    const {categoryLink} = relations;
+
+    categoryLink?.setSlot('content', data.categoryName);
+
+    return relations.secondaryNav.slots({
+      class: 'nav-links-groups',
+      content:
+        (!relations.previousGroupLink && !relations.nextGroupLink
+          ? categoryLink
+          : html.tag('span',
+              {style: relations.colorVariables.slot('color', data.categoryColor).content},
+              [
+                categoryLink.slot('color', false),
+                `(${language.formatUnitList(previousNextPart)})`,
+              ])),
+    });
+  },
+};
diff --git a/src/content/dependencies/generatePageLayout.js b/src/content/dependencies/generatePageLayout.js
index 95a5dbec..cd831ba7 100644
--- a/src/content/dependencies/generatePageLayout.js
+++ b/src/content/dependencies/generatePageLayout.js
@@ -105,7 +105,7 @@ export default {
     color: {validate: v => v.isColor},
 
     styleRules: {
-      validate: v => v.sparseArrayOf(v.isString),
+      validate: v => v.sparseArrayOf(v.isHTML),
       default: [],
     },
 
@@ -183,7 +183,7 @@ export default {
           } else {
             aggregate.call(v.validateProperties({
               path: v.strictArrayOf(v.isString),
-              title: v.isString,
+              title: v.isHTML,
             }), {
               path: object.path,
               title: object.title,
@@ -394,6 +394,10 @@ export default {
 
     const sidebarLeftHTML = generateSidebarHTML('leftSidebar', 'sidebar-left');
     const sidebarRightHTML = generateSidebarHTML('rightSidebar', 'sidebar-right');
+
+    const hasSidebarLeft = !html.isBlank(sidebarLeftHTML);
+    const hasSidebarRight = !html.isBlank(sidebarRightHTML);
+
     const collapseSidebars = slots.leftSidebarCollapse && slots.rightSidebarCollapse;
 
     const hasID = (() => {
@@ -422,20 +426,20 @@ export default {
             processSkippers([
               {condition: true, id: 'content', string: 'content'},
               {
-                condition: !html.isBlank(sidebarLeftHTML),
+                condition: hasSidebarLeft,
                 id: 'sidebar-left',
                 string:
-                  (html.isBlank(sidebarRightHTML)
-                    ? 'sidebar'
-                    : 'sidebar.left'),
+                  (hasSidebarRight
+                    ? 'sidebar.left'
+                    : 'sidebar'),
               },
               {
-                condition: !html.isBlank(sidebarRightHTML),
+                condition: hasSidebarRight,
                 id: 'sidebar-right',
                 string:
-                  (html.isBlank(sidebarLeftHTML)
-                    ? 'sidebar'
-                    : 'sidebar.right'),
+                  (hasSidebarLeft
+                    ? 'sidebar.right'
+                    : 'sidebar'),
               },
               {condition: navHTML, id: 'header', string: 'header'},
               {condition: footerHTML, id: 'footer', string: 'footer'},
@@ -507,11 +511,6 @@ export default {
           class: [
             'layout-columns',
             !collapseSidebars && 'vertical-when-thin',
-            (sidebarLeftHTML || sidebarRightHTML) && 'has-one-sidebar',
-            (sidebarLeftHTML && sidebarRightHTML) && 'has-two-sidebars',
-            !(sidebarLeftHTML || sidebarRightHTML) && 'has-zero-sidebars',
-            sidebarLeftHTML && 'has-sidebar-left',
-            sidebarRightHTML && 'has-sidebar-right',
           ],
         },
         [
@@ -521,7 +520,7 @@ export default {
         ]),
       slots.bannerPosition === 'bottom' && slots.banner,
       footerHTML,
-    ].filter(Boolean).join('\n');
+    ];
 
     const pageHTML = html.tags([
       `<!DOCTYPE html>`,
@@ -609,7 +608,7 @@ export default {
 
             html.tag('link', {
               rel: 'stylesheet',
-              href: to('shared.staticFile', 'site4.css', cachebust),
+              href: to('shared.staticFile', 'site5.css', cachebust),
             }),
 
             html.tag('style', [
@@ -624,12 +623,22 @@ export default {
           ]),
 
           html.tag('body',
-            // {style: body.style || ''},
             [
-              html.tag('div', {id: 'page-container'}, [
-                skippersHTML,
-                layoutHTML,
-              ]),
+              html.tag('div',
+                {
+                  id: 'page-container',
+                  class: [
+                    (hasSidebarLeft || hasSidebarRight) && 'has-one-sidebar',
+                    (hasSidebarLeft && hasSidebarRight) && 'has-two-sidebars',
+                    !(hasSidebarLeft || hasSidebarRight) && 'has-zero-sidebars',
+                    hasSidebarLeft && 'has-sidebar-left',
+                    hasSidebarRight && 'has-sidebar-right',
+                  ],
+                },
+                [
+                  skippersHTML,
+                  layoutHTML,
+                ]),
 
               // infoCardHTML,
               imageOverlayHTML,
diff --git a/src/content/dependencies/generateTrackInfoPage.js b/src/content/dependencies/generateTrackInfoPage.js
index 334c5422..1083d863 100644
--- a/src/content/dependencies/generateTrackInfoPage.js
+++ b/src/content/dependencies/generateTrackInfoPage.js
@@ -44,14 +44,17 @@ export default {
       relation('generatePageLayout');
 
     relations.albumStyleRules =
-      relation('generateAlbumStyleRules', track.album);
+      relation('generateAlbumStyleRules', track.album, track);
 
     relations.socialEmbed =
       relation('generateTrackSocialEmbed', track);
 
     relations.artistChronologyContributions =
       getChronologyRelations(track, {
-        contributions: [...track.artistContribs, ...track.contributorContribs],
+        contributions: [
+          ...track.artistContribs ?? [],
+          ...track.contributorContribs ?? [],
+        ],
 
         linkArtist: artist => relation('linkArtist', artist),
         linkThing: track => relation('linkTrack', track),
@@ -65,7 +68,7 @@ export default {
 
     relations.coverArtistChronologyContributions =
       getChronologyRelations(track, {
-        contributions: track.coverArtistContribs,
+        contributions: track.coverArtistContribs ?? [],
 
         linkArtist: artist => relation('linkArtist', artist),
 
diff --git a/src/content/dependencies/generateTrackList.js b/src/content/dependencies/generateTrackList.js
index f001c3b3..65f5552b 100644
--- a/src/content/dependencies/generateTrackList.js
+++ b/src/content/dependencies/generateTrackList.js
@@ -1,4 +1,4 @@
-import {empty} from '#sugar';
+import {empty, stitchArrays} from '#sugar';
 
 export default {
   contentDependencies: ['linkTrack', 'linkContribution'],
@@ -11,14 +11,17 @@ export default {
     }
 
     return {
-      items: tracks.map(track => ({
-        trackLink:
-          relation('linkTrack', track),
+      trackLinks:
+        tracks
+          .map(track => relation('linkTrack', track)),
 
-        contributionLinks:
-          track.artistContribs
-            .map(contrib => relation('linkContribution', contrib)),
-      })),
+      contributionLinks:
+        tracks
+          .map(track =>
+            (empty(track.artistContribs)
+              ? null
+              : track.artistContribs
+                  .map(contrib => relation('linkContribution', contrib)))),
     };
   },
 
@@ -28,22 +31,28 @@ export default {
   },
 
   generate(relations, slots, {html, language}) {
-    return html.tag('ul',
-      relations.items.map(({trackLink, contributionLinks}) =>
-        html.tag('li',
-          language.$('trackList.item.withArtists', {
-            track: trackLink,
-            by:
-              html.tag('span', {class: 'by'},
-                language.$('trackList.item.withArtists.by', {
-                  artists:
-                    language.formatConjunctionList(
-                      contributionLinks.map(link =>
-                        link.slots({
-                          showContribution: slots.showContribution,
-                          showIcons: slots.showIcons,
-                        }))),
-                })),
-          }))));
+    return (
+      html.tag('ul',
+        stitchArrays({
+          trackLink: relations.trackLinks,
+          contributionLinks: relations.contributionLinks,
+        }).map(({trackLink, contributionLinks}) =>
+            html.tag('li',
+              (empty(contributionLinks)
+                ? trackLink
+                : language.$('trackList.item.withArtists', {
+                    track: trackLink,
+                    by:
+                      html.tag('span', {class: 'by'},
+                        language.$('trackList.item.withArtists.by', {
+                          artists:
+                            language.formatConjunctionList(
+                              contributionLinks.map(link =>
+                                link.slots({
+                                  showContribution: slots.showContribution,
+                                  showIcons: slots.showIcons,
+                                }))),
+                        })),
+                  }))))));
   },
 };
diff --git a/src/content/dependencies/generateWikiHomeAlbumsRow.js b/src/content/dependencies/generateWikiHomeAlbumsRow.js
index 99c1be55..cb0860f5 100644
--- a/src/content/dependencies/generateWikiHomeAlbumsRow.js
+++ b/src/content/dependencies/generateWikiHomeAlbumsRow.js
@@ -16,7 +16,7 @@ export default {
   sprawl({albumData}, row) {
     const sprawl = {};
 
-    switch (row.sourceGroupByRef) {
+    switch (row.sourceGroup) {
       case 'new-releases':
         sprawl.albums = getNewReleases(row.countAlbumsFromGroup, {albumData});
         break;
diff --git a/src/content/dependencies/image.js b/src/content/dependencies/image.js
index 71b905f7..6c0aeecd 100644
--- a/src/content/dependencies/image.js
+++ b/src/content/dependencies/image.js
@@ -1,11 +1,16 @@
+import {logInfo, logWarn} from '#cli';
 import {empty} from '#sugar';
 
 export default {
   extraDependencies: [
-    'getSizeOfImageFile',
+    'checkIfImagePathHasCachedThumbnails',
+    'getDimensionsOfImagePath',
+    'getSizeOfImagePath',
+    'getThumbnailEqualOrSmaller',
+    'getThumbnailsAvailableForDimensions',
     'html',
     'language',
-    'thumb',
+    'missingImagePaths',
     'to',
   ],
 
@@ -52,10 +57,14 @@ export default {
   },
 
   generate(data, slots, {
-    getSizeOfImageFile,
+    checkIfImagePathHasCachedThumbnails,
+    getDimensionsOfImagePath,
+    getSizeOfImagePath,
+    getThumbnailEqualOrSmaller,
+    getThumbnailsAvailableForDimensions,
     html,
     language,
-    thumb,
+    missingImagePaths,
     to,
   }) {
     let originalSrc;
@@ -68,43 +77,48 @@ export default {
       originalSrc = '';
     }
 
-    const thumbSrc =
-      originalSrc &&
-        (slots.thumb
-          ? thumb[slots.thumb](originalSrc)
-          : originalSrc);
+    let mediaSrc = null;
+    if (originalSrc.startsWith(to('media.root'))) {
+      mediaSrc =
+        originalSrc
+          .slice(to('media.root').length)
+          .replace(/^\//, '');
+    }
 
-    const willLink = typeof slots.link === 'string' || slots.link;
-    const customLink = typeof slots.link === 'string';
+    const isMissingImageFile =
+      missingImagePaths.includes(mediaSrc);
+
+    if (isMissingImageFile) {
+      logInfo`No image file for ${mediaSrc} - build again for list of missing images.`;
+    }
+
+    const willLink =
+      !isMissingImageFile &&
+      (typeof slots.link === 'string' || slots.link);
+
+    const customLink =
+      typeof slots.link === 'string';
 
     const willReveal =
       slots.reveal &&
       originalSrc &&
+      !isMissingImageFile &&
       !empty(data.contentWarnings);
 
     const willSquare = slots.square;
 
     const idOnImg = willLink ? null : slots.id;
     const idOnLink = willLink ? slots.id : null;
+
     const classOnImg = willLink ? null : slots.class;
     const classOnLink = willLink ? slots.class : null;
 
-    if (!originalSrc) {
+    if (!originalSrc || isMissingImageFile) {
       return prepare(
         html.tag('div', {class: 'image-text-area'},
-          slots.missingSourceContent));
-    }
-
-    let fileSize = null;
-    if (willLink) {
-      const mediaRoot = to('media.root');
-      if (originalSrc.startsWith(mediaRoot)) {
-        fileSize =
-          getSizeOfImageFile(
-            originalSrc
-              .slice(mediaRoot.length)
-              .replace(/^\//, ''));
-      }
+          (html.isBlank(slots.missingSourceContent)
+            ? language.$(`misc.missingImage`)
+            : slots.missingSourceContent)));
     }
 
     let reveal = null;
@@ -119,22 +133,84 @@ export default {
       ];
     }
 
+    const hasThumbnails =
+      mediaSrc &&
+      checkIfImagePathHasCachedThumbnails(mediaSrc);
+
+    // Warn for images that *should* have cached thumbnail information but are
+    // missing from the thumbs cache.
+    if (
+      slots.thumb &&
+      !hasThumbnails &&
+      !mediaSrc.endsWith('.gif')
+    ) {
+      logWarn`No thumbnail info cached: ${mediaSrc} - displaying original image here (instead of ${slots.thumb})`;
+    }
+
+    // Important to note that these might not be set at all, even if
+    // slots.thumb was provided.
+    let thumbSrc = null;
+    let availableThumbs = null;
+    let originalLength = null;
+
+    if (hasThumbnails && slots.thumb) {
+      // Note: This provides mediaSrc to getThumbnailEqualOrSmaller, since
+      // it's the identifier which thumbnail utilities use to query from the
+      // thumbnail cache. But we use the result to operate on originalSrc,
+      // which is the HTML output-appropriate path including `../../` or
+      // another alternate base path.
+      const selectedSize = getThumbnailEqualOrSmaller(slots.thumb, mediaSrc);
+      thumbSrc = originalSrc.replace(/\.(jpg|png)$/, `.${selectedSize}.jpg`);
+
+      const dimensions = getDimensionsOfImagePath(mediaSrc);
+      availableThumbs = getThumbnailsAvailableForDimensions(dimensions);
+
+      const [width, height] = dimensions;
+      originalLength = Math.max(width, height)
+    }
+
+    let fileSize = null;
+    if (willLink && mediaSrc) {
+      fileSize = getSizeOfImagePath(mediaSrc);
+    }
+
     const imgAttributes = {
       id: idOnImg,
       class: classOnImg,
       alt: slots.alt,
       width: slots.width,
       height: slots.height,
-      'data-original-size': fileSize,
-      'data-no-image-preview': customLink,
     };
 
+    if (customLink) {
+      imgAttributes['data-no-image-preview'] = true;
+    }
+
+    // These attributes are only relevant when a thumbnail are available *and*
+    // being used.
+    if (hasThumbnails && slots.thumb) {
+      if (fileSize) {
+        imgAttributes['data-original-size'] = fileSize;
+      }
+
+      if (originalLength) {
+        imgAttributes['data-original-length'] = originalLength;
+      }
+
+      if (!empty(availableThumbs)) {
+        imgAttributes['data-thumbs'] =
+          availableThumbs
+            .map(([name, size]) => `${name}:${size}`)
+            .join(' ');
+      }
+    }
+
     const nonlazyHTML =
       originalSrc &&
         prepare(
           html.tag('img', {
             ...imgAttributes,
-            src: thumbSrc,
+            src: thumbSrc ?? originalSrc,
           }));
 
     if (slots.lazy) {
@@ -145,7 +221,7 @@ export default {
             {
               ...imgAttributes,
               class: 'lazy',
-              'data-original': thumbSrc,
+              'data-original': thumbSrc ?? originalSrc,
             }),
           true),
       ]);
diff --git a/src/content/dependencies/index.js b/src/content/dependencies/index.js
index 3bc34845..58bac0d2 100644
--- a/src/content/dependencies/index.js
+++ b/src/content/dependencies/index.js
@@ -6,7 +6,7 @@ import {fileURLToPath} from 'node:url';
 import chokidar from 'chokidar';
 import {ESLint} from 'eslint';
 
-import {color, logWarn} from '#cli';
+import {colors, logWarn} from '#cli';
 import contentFunction, {ContentFunctionSpecError} from '#content-function';
 import {annotateFunction} from '#sugar';
 
@@ -30,7 +30,6 @@ export function watchContentDependencies({
   const contentDependencies = {};
 
   let emittedReady = false;
-  let allDependenciesFulfilled = false;
   let closed = false;
 
   let _close = () => {};
@@ -77,12 +76,12 @@ export function watchContentDependencies({
   // prematurely find out there aren't any nulls - before the nulls have
   // been entered at all!).
 
-  readdir(metaDirname).then(files => {
+  readdir(watchPath).then(files => {
     if (closed) {
       return;
     }
 
-    const filePaths = files.map(file => path.join(metaDirname, file));
+    const filePaths = files.map(file => path.join(watchPath, file));
     for (const filePath of filePaths) {
       if (filePath === metaPath) continue;
       const functionName = getFunctionName(filePath);
@@ -91,7 +90,7 @@ export function watchContentDependencies({
       }
     }
 
-    const watcher = chokidar.watch(metaDirname);
+    const watcher = chokidar.watch(watchPath);
 
     watcher.on('all', (event, filePath) => {
       if (!['add', 'change'].includes(event)) return;
@@ -178,7 +177,14 @@ export function watchContentDependencies({
       // Just skip newly created files. They'll be processed again when
       // written.
       if (spec === undefined) {
-        contentDependencies[functionName] = null;
+        // For practical purposes the file is treated as though it doesn't
+        // even exist (undefined), rather than not being ready yet (null).
+        // Apart from if existing contents of the file were erased (but not
+        // the file itself), this value might already be set (to null!) by
+        // the readdir performed at the beginning to evaluate which files
+        // should be read and processed at least once before reporting all
+        // dependencies as ready.
+        delete contentDependencies[functionName];
         return;
       }
 
@@ -192,7 +198,7 @@ export function watchContentDependencies({
 
       if (logging && emittedReady) {
         const timestamp = new Date().toLocaleString('en-US', {timeStyle: 'medium'});
-        console.log(color.green(`[${timestamp}] Updated ${functionName}`));
+        console.log(colors.green(`[${timestamp}] Updated ${functionName}`));
       }
 
       contentDependencies[functionName] = fn;
@@ -219,9 +225,9 @@ export function watchContentDependencies({
       }
 
       if (typeof error === 'string') {
-        console.error(color.yellow(error));
+        console.error(colors.yellow(error));
       } else if (error instanceof ContentFunctionSpecError) {
-        console.error(color.yellow(error.message));
+        console.error(colors.yellow(error.message));
       } else {
         console.error(error);
       }
diff --git a/src/content/dependencies/linkAlbumDynamically.js b/src/content/dependencies/linkAlbumDynamically.js
new file mode 100644
index 00000000..3adc64df
--- /dev/null
+++ b/src/content/dependencies/linkAlbumDynamically.js
@@ -0,0 +1,14 @@
+export default {
+  contentDependencies: ['linkAlbumGallery', 'linkAlbum'],
+  extraDependencies: ['pagePath'],
+
+  relations: (relation, album) => ({
+    galleryLink: relation('linkAlbumGallery', album),
+    infoLink: relation('linkAlbum', album),
+  }),
+
+  generate: (relations, {pagePath}) =>
+    (pagePath[0] === 'albumGallery'
+      ? relations.galleryLink
+      : relations.infoLink),
+};
diff --git a/src/content/dependencies/linkFlashAct.js b/src/content/dependencies/linkFlashAct.js
new file mode 100644
index 00000000..fbb819ed
--- /dev/null
+++ b/src/content/dependencies/linkFlashAct.js
@@ -0,0 +1,14 @@
+export default {
+  contentDependencies: ['linkThing'],
+  extraDependencies: ['html'],
+
+  relations: (relation, flashAct) =>
+    ({link: relation('linkThing', 'localized.flashActGallery', flashAct)}),
+
+  data: (flashAct) =>
+    ({name: flashAct.name}),
+
+  generate: (data, relations, {html}) =>
+    relations.link
+      .slot('content', new html.Tag(null, null, data.name)),
+};
diff --git a/src/content/dependencies/linkGroupDynamically.js b/src/content/dependencies/linkGroupDynamically.js
new file mode 100644
index 00000000..90303ed1
--- /dev/null
+++ b/src/content/dependencies/linkGroupDynamically.js
@@ -0,0 +1,14 @@
+export default {
+  contentDependencies: ['linkGroupGallery', 'linkGroup'],
+  extraDependencies: ['pagePath'],
+
+  relations: (relation, group) => ({
+    galleryLink: relation('linkGroupGallery', group),
+    infoLink: relation('linkGroup', group),
+  }),
+
+  generate: (relations, {pagePath}) =>
+    (pagePath[0] === 'groupGallery'
+      ? relations.galleryLink
+      : relations.infoLink),
+};
diff --git a/src/content/dependencies/linkTemplate.js b/src/content/dependencies/linkTemplate.js
index 1cf64c59..d9af726c 100644
--- a/src/content/dependencies/linkTemplate.js
+++ b/src/content/dependencies/linkTemplate.js
@@ -15,8 +15,9 @@ export default {
     href: {type: 'string'},
     path: {validate: v => v.validateArrayItems(v.isString)},
     hash: {type: 'string'},
+    linkless: {type: 'boolean', default: false},
 
-    tooltip: {validate: v => v.isString},
+    tooltip: {type: 'string'},
     attributes: {validate: v => v.isAttributes},
     color: {validate: v => v.isColor},
     content: {type: 'html'},
@@ -29,27 +30,33 @@ export default {
     language,
     to,
   }) {
-    let href = slots.href;
+    let href;
     let style;
     let title;
 
-    if (href) {
-      href = encodeURI(href);
-    } else if (!empty(slots.path)) {
-      href = to(...slots.path);
-    }
+    if (slots.linkless) {
+      href = null;
+    } else {
+      if (slots.href) {
+        href = encodeURI(slots.href);
+      } else if (!empty(slots.path)) {
+        href = to(...slots.path);
+      } else {
+        href = '';
+      }
 
-    if (appendIndexHTML) {
-      if (
-        /^(?!https?:\/\/).+\/$/.test(href) &&
-        href.endsWith('/')
-      ) {
-        href += 'index.html';
+      if (appendIndexHTML) {
+        if (
+          /^(?!https?:\/\/).+\/$/.test(href) &&
+          href.endsWith('/')
+        ) {
+          href += 'index.html';
+        }
       }
-    }
 
-    if (slots.hash) {
-      href += (slots.hash.startsWith('#') ? '' : '#') + slots.hash;
+      if (slots.hash) {
+        href += (slots.hash.startsWith('#') ? '' : '#') + slots.hash;
+      }
     }
 
     if (slots.color) {
diff --git a/src/content/dependencies/linkThing.js b/src/content/dependencies/linkThing.js
index e3e2608f..b20b132b 100644
--- a/src/content/dependencies/linkThing.js
+++ b/src/content/dependencies/linkThing.js
@@ -1,6 +1,6 @@
 export default {
   contentDependencies: ['linkTemplate'],
-  extraDependencies: ['html'],
+  extraDependencies: ['html', 'language'],
 
   relations(relation) {
     return {
@@ -26,7 +26,7 @@ export default {
     preferShortName: {type: 'boolean', default: false},
 
     tooltip: {
-      validate: v => v.oneOf(v.isBoolean, v.isString),
+      validate: v => v.oneOf(v.isBoolean, v.isHTML),
       default: false,
     },
 
@@ -36,12 +36,13 @@ export default {
     },
 
     anchor: {type: 'boolean', default: false},
+    linkless: {type: 'boolean', default: false},
 
     attributes: {validate: v => v.isAttributes},
     hash: {type: 'string'},
   },
 
-  generate(data, relations, slots, {html}) {
+  generate(data, relations, slots, {html, language}) {
     const path = [data.pathKey, data.directory];
 
     const name =
@@ -51,7 +52,7 @@ export default {
 
     const content =
       (html.isBlank(slots.content)
-        ? name
+        ? language.sanitize(name)
         : slots.content);
 
     let color = null;
@@ -78,6 +79,7 @@ export default {
 
         attributes: slots.attributes,
         hash: slots.hash,
+        linkless: slots.linkless,
       });
   },
 }
diff --git a/src/content/dependencies/listArtTagNetwork.js b/src/content/dependencies/listArtTagNetwork.js
new file mode 100644
index 00000000..b3a54747
--- /dev/null
+++ b/src/content/dependencies/listArtTagNetwork.js
@@ -0,0 +1 @@
+export default {generate() {}};
diff --git a/src/content/dependencies/listTracksWithExtra.js b/src/content/dependencies/listTracksWithExtra.js
index 73d25e3d..c9f80f35 100644
--- a/src/content/dependencies/listTracksWithExtra.js
+++ b/src/content/dependencies/listTracksWithExtra.js
@@ -65,10 +65,14 @@ export default {
         stitchArrays({
           albumLink: relations.albumLinks,
           date: data.dates,
-        }).map(({albumLink, date}) => ({
-            album: albumLink,
-            date: language.formatDate(date),
-          })),
+        }).map(({albumLink, date}) =>
+            (date
+              ? {
+                  stringsKey: 'withDate',
+                  album: albumLink,
+                  date: language.formatDate(date),
+                }
+              : {album: albumLink})),
 
       chunkRows:
         relations.trackLinks
diff --git a/src/content/dependencies/transformContent.js b/src/content/dependencies/transformContent.js
index 9a5ac456..3c2c3521 100644
--- a/src/content/dependencies/transformContent.js
+++ b/src/content/dependencies/transformContent.js
@@ -53,6 +53,10 @@ export const replacerSpec = {
       }
     },
   },
+  'flash-act': {
+    find: 'flashAct',
+    link: 'flashAct',
+  },
   group: {
     find: 'group',
     link: 'groupInfo',
@@ -119,6 +123,7 @@ const linkThingRelationMap = {
   artist: 'linkArtist',
   artistGallery: 'linkArtistGallery',
   flash: 'linkFlash',
+  flashAct: 'linkFlashAct',
   groupInfo: 'linkGroup',
   groupGallery: 'linkGroupGallery',
   listing: 'linkListing',
diff --git a/src/data/composite/control-flow/exitWithoutDependency.js b/src/data/composite/control-flow/exitWithoutDependency.js
new file mode 100644
index 00000000..c660a7ef
--- /dev/null
+++ b/src/data/composite/control-flow/exitWithoutDependency.js
@@ -0,0 +1,35 @@
+// Early exits if a dependency isn't available.
+// See withResultOfAvailabilityCheck for {mode} options.
+
+import {input, templateCompositeFrom} from '#composite';
+
+import inputAvailabilityCheckMode from './inputAvailabilityCheckMode.js';
+import withResultOfAvailabilityCheck from './withResultOfAvailabilityCheck.js';
+
+export default templateCompositeFrom({
+  annotation: `exitWithoutDependency`,
+
+  inputs: {
+    dependency: input({acceptsNull: true}),
+    mode: inputAvailabilityCheckMode(),
+    value: input({defaultValue: null}),
+  },
+
+  steps: () => [
+    withResultOfAvailabilityCheck({
+      from: input('dependency'),
+      mode: input('mode'),
+    }),
+
+    {
+      dependencies: ['#availability', input('value')],
+      compute: (continuation, {
+        ['#availability']: availability,
+        [input('value')]: value,
+      }) =>
+        (availability
+          ? continuation()
+          : continuation.exit(value)),
+    },
+  ],
+});
diff --git a/src/data/composite/control-flow/exitWithoutUpdateValue.js b/src/data/composite/control-flow/exitWithoutUpdateValue.js
new file mode 100644
index 00000000..244b3233
--- /dev/null
+++ b/src/data/composite/control-flow/exitWithoutUpdateValue.js
@@ -0,0 +1,24 @@
+// Early exits if this property's update value isn't available.
+// See withResultOfAvailabilityCheck for {mode} options.
+
+import {input, templateCompositeFrom} from '#composite';
+
+import exitWithoutDependency from './exitWithoutDependency.js';
+import inputAvailabilityCheckMode from './inputAvailabilityCheckMode.js';
+
+export default templateCompositeFrom({
+  annotation: `exitWithoutUpdateValue`,
+
+  inputs: {
+    mode: inputAvailabilityCheckMode(),
+    value: input({defaultValue: null}),
+  },
+
+  steps: () => [
+    exitWithoutDependency({
+      dependency: input.updateValue(),
+      mode: input('mode'),
+      value: input('value'),
+    }),
+  ],
+});
diff --git a/src/data/composite/control-flow/exposeConstant.js b/src/data/composite/control-flow/exposeConstant.js
new file mode 100644
index 00000000..e0435478
--- /dev/null
+++ b/src/data/composite/control-flow/exposeConstant.js
@@ -0,0 +1,26 @@
+// Exposes a constant value exactly as it is; like exposeDependency, this
+// is typically the base of a composition serving as a particular property
+// descriptor. It generally follows steps which will conditionally early
+// exit with some other value, with the exposeConstant base serving as the
+// fallback default value.
+
+import {input, templateCompositeFrom} from '#composite';
+
+export default templateCompositeFrom({
+  annotation: `exposeConstant`,
+
+  compose: false,
+
+  inputs: {
+    value: input.staticValue(),
+  },
+
+  steps: () => [
+    {
+      dependencies: [input('value')],
+      compute: ({
+        [input('value')]: value,
+      }) => value,
+    },
+  ],
+});
diff --git a/src/data/composite/control-flow/exposeDependency.js b/src/data/composite/control-flow/exposeDependency.js
new file mode 100644
index 00000000..3aa3d03a
--- /dev/null
+++ b/src/data/composite/control-flow/exposeDependency.js
@@ -0,0 +1,28 @@
+// Exposes a dependency exactly as it is; this is typically the base of a
+// composition which was created to serve as one property's descriptor.
+//
+// Please note that this *doesn't* verify that the dependency exists, so
+// if you provide the wrong name or it hasn't been set by a previous
+// compositional step, the property will be exposed as undefined instead
+// of null.
+
+import {input, templateCompositeFrom} from '#composite';
+
+export default templateCompositeFrom({
+  annotation: `exposeDependency`,
+
+  compose: false,
+
+  inputs: {
+    dependency: input.staticDependency({acceptsNull: true}),
+  },
+
+  steps: () => [
+    {
+      dependencies: [input('dependency')],
+      compute: ({
+        [input('dependency')]: dependency
+      }) => dependency,
+    },
+  ],
+});
diff --git a/src/data/composite/control-flow/exposeDependencyOrContinue.js b/src/data/composite/control-flow/exposeDependencyOrContinue.js
new file mode 100644
index 00000000..0f7f223e
--- /dev/null
+++ b/src/data/composite/control-flow/exposeDependencyOrContinue.js
@@ -0,0 +1,34 @@
+// Exposes a dependency as it is, or continues if it's unavailable.
+// See withResultOfAvailabilityCheck for {mode} options.
+
+import {input, templateCompositeFrom} from '#composite';
+
+import inputAvailabilityCheckMode from './inputAvailabilityCheckMode.js';
+import withResultOfAvailabilityCheck from './withResultOfAvailabilityCheck.js';
+
+export default templateCompositeFrom({
+  annotation: `exposeDependencyOrContinue`,
+
+  inputs: {
+    dependency: input({acceptsNull: true}),
+    mode: inputAvailabilityCheckMode(),
+  },
+
+  steps: () => [
+    withResultOfAvailabilityCheck({
+      from: input('dependency'),
+      mode: input('mode'),
+    }),
+
+    {
+      dependencies: ['#availability', input('dependency')],
+      compute: (continuation, {
+        ['#availability']: availability,
+        [input('dependency')]: dependency,
+      }) =>
+        (availability
+          ? continuation.exit(dependency)
+          : continuation()),
+    },
+  ],
+});
diff --git a/src/data/composite/control-flow/exposeUpdateValueOrContinue.js b/src/data/composite/control-flow/exposeUpdateValueOrContinue.js
new file mode 100644
index 00000000..1f94b332
--- /dev/null
+++ b/src/data/composite/control-flow/exposeUpdateValueOrContinue.js
@@ -0,0 +1,40 @@
+// Exposes the update value of an {update: true} property as it is,
+// or continues if it's unavailable.
+//
+// See withResultOfAvailabilityCheck for {mode} options.
+//
+// Provide {validate} here to conveniently set a custom validation check
+// for this property's update value.
+//
+
+import {input, templateCompositeFrom} from '#composite';
+
+import exposeDependencyOrContinue from './exposeDependencyOrContinue.js';
+import inputAvailabilityCheckMode from './inputAvailabilityCheckMode.js';
+
+export default templateCompositeFrom({
+  annotation: `exposeUpdateValueOrContinue`,
+
+  inputs: {
+    mode: inputAvailabilityCheckMode(),
+
+    validate: input({
+      type: 'function',
+      defaultValue: null,
+    }),
+  },
+
+  update: ({
+    [input.staticValue('validate')]: validate,
+  }) =>
+    (validate
+      ? {validate}
+      : {}),
+
+  steps: () => [
+    exposeDependencyOrContinue({
+      dependency: input.updateValue(),
+      mode: input('mode'),
+    }),
+  ],
+});
diff --git a/src/data/composite/control-flow/index.js b/src/data/composite/control-flow/index.js
new file mode 100644
index 00000000..dfc53db7
--- /dev/null
+++ b/src/data/composite/control-flow/index.js
@@ -0,0 +1,9 @@
+export {default as exitWithoutDependency} from './exitWithoutDependency.js';
+export {default as exitWithoutUpdateValue} from './exitWithoutUpdateValue.js';
+export {default as exposeConstant} from './exposeConstant.js';
+export {default as exposeDependency} from './exposeDependency.js';
+export {default as exposeDependencyOrContinue} from './exposeDependencyOrContinue.js';
+export {default as exposeUpdateValueOrContinue} from './exposeUpdateValueOrContinue.js';
+export {default as raiseOutputWithoutDependency} from './raiseOutputWithoutDependency.js';
+export {default as raiseOutputWithoutUpdateValue} from './raiseOutputWithoutUpdateValue.js';
+export {default as withResultOfAvailabilityCheck} from './withResultOfAvailabilityCheck.js';
diff --git a/src/data/composite/control-flow/inputAvailabilityCheckMode.js b/src/data/composite/control-flow/inputAvailabilityCheckMode.js
new file mode 100644
index 00000000..8008fdeb
--- /dev/null
+++ b/src/data/composite/control-flow/inputAvailabilityCheckMode.js
@@ -0,0 +1,9 @@
+import {input} from '#composite';
+import {is} from '#validators';
+
+export default function inputAvailabilityCheckMode() {
+  return input({
+    validate: is('null', 'empty', 'falsy', 'index'),
+    defaultValue: 'null',
+  });
+}
diff --git a/src/data/composite/control-flow/raiseOutputWithoutDependency.js b/src/data/composite/control-flow/raiseOutputWithoutDependency.js
new file mode 100644
index 00000000..03d8036a
--- /dev/null
+++ b/src/data/composite/control-flow/raiseOutputWithoutDependency.js
@@ -0,0 +1,39 @@
+// Raises if a dependency isn't available.
+// See withResultOfAvailabilityCheck for {mode} options.
+
+import {input, templateCompositeFrom} from '#composite';
+
+import inputAvailabilityCheckMode from './inputAvailabilityCheckMode.js';
+import withResultOfAvailabilityCheck from './withResultOfAvailabilityCheck.js';
+
+export default templateCompositeFrom({
+  annotation: `raiseOutputWithoutDependency`,
+
+  inputs: {
+    dependency: input({acceptsNull: true}),
+    mode: inputAvailabilityCheckMode(),
+    output: input.staticValue({defaultValue: {}}),
+  },
+
+  outputs: ({
+    [input.staticValue('output')]: output,
+  }) => Object.keys(output),
+
+  steps: () => [
+    withResultOfAvailabilityCheck({
+      from: input('dependency'),
+      mode: input('mode'),
+    }),
+
+    {
+      dependencies: ['#availability', input('output')],
+      compute: (continuation, {
+        ['#availability']: availability,
+        [input('output')]: output,
+      }) =>
+        (availability
+          ? continuation()
+          : continuation.raiseOutputAbove(output)),
+    },
+  ],
+});
diff --git a/src/data/composite/control-flow/raiseOutputWithoutUpdateValue.js b/src/data/composite/control-flow/raiseOutputWithoutUpdateValue.js
new file mode 100644
index 00000000..3c39f5ba
--- /dev/null
+++ b/src/data/composite/control-flow/raiseOutputWithoutUpdateValue.js
@@ -0,0 +1,47 @@
+// Raises if this property's update value isn't available.
+// See withResultOfAvailabilityCheck for {mode} options!
+
+import {input, templateCompositeFrom} from '#composite';
+
+import inputAvailabilityCheckMode from './inputAvailabilityCheckMode.js';
+import withResultOfAvailabilityCheck from './withResultOfAvailabilityCheck.js';
+
+export default templateCompositeFrom({
+  annotation: `raiseOutputWithoutUpdateValue`,
+
+  inputs: {
+    mode: inputAvailabilityCheckMode(),
+    output: input.staticValue({defaultValue: {}}),
+  },
+
+  outputs: ({
+    [input.staticValue('output')]: output,
+  }) => Object.keys(output),
+
+  steps: () => [
+    withResultOfAvailabilityCheck({
+      from: input.updateValue(),
+      mode: input('mode'),
+    }),
+
+    // TODO: A bit of a kludge, below. Other "do something with the update
+    // value" type functions can get by pretty much just passing that value
+    // as an input (input.updateValue()) into the corresponding "do something
+    // with a dependency/arbitrary value" function. But we can't do that here,
+    // because the special behavior, raiseOutputAbove(), only works to raise
+    // output above the composition it's *directly* nested in. Other languages
+    // have a throw/catch system that might serve as inspiration for something
+    // better here.
+
+    {
+      dependencies: ['#availability', input('output')],
+      compute: (continuation, {
+        ['#availability']: availability,
+        [input('output')]: output,
+      }) =>
+        (availability
+          ? continuation()
+          : continuation.raiseOutputAbove(output)),
+    },
+  ],
+});
diff --git a/src/data/composite/control-flow/withResultOfAvailabilityCheck.js b/src/data/composite/control-flow/withResultOfAvailabilityCheck.js
new file mode 100644
index 00000000..a6942014
--- /dev/null
+++ b/src/data/composite/control-flow/withResultOfAvailabilityCheck.js
@@ -0,0 +1,71 @@
+// Checks the availability of a dependency and provides the result to later
+// steps under '#availability' (by default). This is mainly intended for use
+// by the more specific utilities, which you should consider using instead.
+//
+// Customize {mode} to select one of these modes, or default to 'null':
+//
+// * 'null':  Check that the value isn't null (and not undefined either).
+// * 'empty': Check that the value is neither null, undefined, nor an empty
+//            array.
+// * 'falsy': Check that the value isn't false when treated as a boolean
+//            (nor an empty array). Keep in mind this will also be false
+//            for values like zero and the empty string!
+// * 'index': Check that the value is a number, and is at least zero.
+//
+// See also:
+//  - exitWithoutDependency
+//  - exitWithoutUpdateValue
+//  - exposeDependencyOrContinue
+//  - exposeUpdateValueOrContinue
+//  - raiseOutputWithoutDependency
+//  - raiseOutputWithoutUpdateValue
+//
+
+import {input, templateCompositeFrom} from '#composite';
+import {empty} from '#sugar';
+
+import inputAvailabilityCheckMode from './inputAvailabilityCheckMode.js';
+
+export default templateCompositeFrom({
+  annotation: `withResultOfAvailabilityCheck`,
+
+  inputs: {
+    from: input({acceptsNull: true}),
+    mode: inputAvailabilityCheckMode(),
+  },
+
+  outputs: ['#availability'],
+
+  steps: () => [
+    {
+      dependencies: [input('from'), input('mode')],
+
+      compute: (continuation, {
+        [input('from')]: value,
+        [input('mode')]: mode,
+      }) => {
+        let availability;
+
+        switch (mode) {
+          case 'null':
+            availability = value !== undefined && value !== null;
+            break;
+
+          case 'empty':
+            availability = value !== undefined && !empty(value);
+            break;
+
+          case 'falsy':
+            availability = !!value && (!Array.isArray(value) || !empty(value));
+            break;
+
+          case 'index':
+            availability = typeof value === 'number' && value >= 0;
+            break;
+        }
+
+        return continuation({'#availability': availability});
+      },
+    },
+  ],
+});
diff --git a/src/data/composite/data/excludeFromList.js b/src/data/composite/data/excludeFromList.js
new file mode 100644
index 00000000..718f2294
--- /dev/null
+++ b/src/data/composite/data/excludeFromList.js
@@ -0,0 +1,56 @@
+// Filters particular values out of a list. Note that this will always
+// completely skip over null, but can be used to filter out any other
+// primitive or object value.
+//
+// See also:
+//  - fillMissingListItems
+//
+// More list utilities:
+//  - withFlattenedList
+//  - withPropertyFromList
+//  - withPropertiesFromList
+//  - withUnflattenedList
+//
+
+import {input, templateCompositeFrom} from '#composite';
+import {empty} from '#sugar';
+
+export default templateCompositeFrom({
+  annotation: `excludeFromList`,
+
+  inputs: {
+    list: input(),
+
+    item: input({defaultValue: null}),
+    items: input({type: 'array', defaultValue: null}),
+  },
+
+  outputs: ({
+    [input.staticDependency('list')]: list,
+  }) => [list ?? '#list'],
+
+  steps: () => [
+    {
+      dependencies: [
+        input.staticDependency('list'),
+        input('list'),
+        input('item'),
+        input('items'),
+      ],
+
+      compute: (continuation, {
+        [input.staticDependency('list')]: listName,
+        [input('list')]: listContents,
+        [input('item')]: excludeItem,
+        [input('items')]: excludeItems,
+      }) => continuation({
+        [listName ?? '#list']:
+          listContents.filter(item => {
+            if (excludeItem !== null && item === excludeItem) return false;
+            if (!empty(excludeItems) && excludeItems.includes(item)) return false;
+            return true;
+          }),
+      }),
+    },
+  ],
+});
diff --git a/src/data/composite/data/fillMissingListItems.js b/src/data/composite/data/fillMissingListItems.js
new file mode 100644
index 00000000..c06eceda
--- /dev/null
+++ b/src/data/composite/data/fillMissingListItems.js
@@ -0,0 +1,51 @@
+// Replaces items of a list, which are null or undefined, with some fallback
+// value. By default, this replaces the passed dependency.
+//
+// See also:
+//  - excludeFromList
+//
+// More list utilities:
+//  - withFlattenedList
+//  - withPropertyFromList
+//  - withPropertiesFromList
+//  - withUnflattenedList
+//
+
+import {input, templateCompositeFrom} from '#composite';
+
+export default templateCompositeFrom({
+  annotation: `fillMissingListItems`,
+
+  inputs: {
+    list: input({type: 'array'}),
+    fill: input({acceptsNull: true}),
+  },
+
+  outputs: ({
+    [input.staticDependency('list')]: list,
+  }) => [list ?? '#list'],
+
+  steps: () => [
+    {
+      dependencies: [input('list'), input('fill')],
+      compute: (continuation, {
+        [input('list')]: list,
+        [input('fill')]: fill,
+      }) => continuation({
+        ['#filled']:
+          list.map(item => item ?? fill),
+      }),
+    },
+
+    {
+      dependencies: [input.staticDependency('list'), '#filled'],
+      compute: (continuation, {
+        [input.staticDependency('list')]: list,
+        ['#filled']: filled,
+      }) => continuation({
+        [list ?? '#list']:
+          filled,
+      }),
+    },
+  ],
+});
diff --git a/src/data/composite/data/index.js b/src/data/composite/data/index.js
new file mode 100644
index 00000000..ecd05129
--- /dev/null
+++ b/src/data/composite/data/index.js
@@ -0,0 +1,8 @@
+export {default as excludeFromList} from './excludeFromList.js';
+export {default as fillMissingListItems} from './fillMissingListItems.js';
+export {default as withFlattenedList} from './withFlattenedList.js';
+export {default as withPropertiesFromList} from './withPropertiesFromList.js';
+export {default as withPropertiesFromObject} from './withPropertiesFromObject.js';
+export {default as withPropertyFromList} from './withPropertyFromList.js';
+export {default as withPropertyFromObject} from './withPropertyFromObject.js';
+export {default as withUnflattenedList} from './withUnflattenedList.js';
diff --git a/src/data/composite/data/withFlattenedList.js b/src/data/composite/data/withFlattenedList.js
new file mode 100644
index 00000000..b08edb4e
--- /dev/null
+++ b/src/data/composite/data/withFlattenedList.js
@@ -0,0 +1,47 @@
+// Flattens an array with one level of nested arrays, providing as dependencies
+// both the flattened array as well as the original starting indices of each
+// successive source array.
+//
+// See also:
+//  - withFlattenedList
+//
+// More list utilities:
+//  - excludeFromList
+//  - fillMissingListItems
+//  - withPropertyFromList
+//  - withPropertiesFromList
+//
+
+import {input, templateCompositeFrom} from '#composite';
+
+export default templateCompositeFrom({
+  annotation: `withFlattenedList`,
+
+  inputs: {
+    list: input({type: 'array'}),
+  },
+
+  outputs: ['#flattenedList', '#flattenedIndices'],
+
+  steps: () => [
+    {
+      dependencies: [input('list')],
+      compute(continuation, {
+        [input('list')]: sourceList,
+      }) {
+        const flattenedList = sourceList.flat();
+        const indices = [];
+        let lastEndIndex = 0;
+        for (const {length} of sourceList) {
+          indices.push(lastEndIndex);
+          lastEndIndex += length;
+        }
+
+        return continuation({
+          ['#flattenedList']: flattenedList,
+          ['#flattenedIndices']: indices,
+        });
+      },
+    },
+  ],
+});
diff --git a/src/data/composite/data/withPropertiesFromList.js b/src/data/composite/data/withPropertiesFromList.js
new file mode 100644
index 00000000..76ba696c
--- /dev/null
+++ b/src/data/composite/data/withPropertiesFromList.js
@@ -0,0 +1,92 @@
+// Gets the listed properties from each of a list of objects, providing lists
+// of property values each into a dependency prefixed with the same name as the
+// list (by default).
+//
+// Like withPropertyFromList, this doesn't alter indices.
+//
+// See also:
+//  - withPropertiesFromObject
+//  - withPropertyFromList
+//
+// More list utilities:
+//  - excludeFromList
+//  - fillMissingListItems
+//  - withFlattenedList
+//  - withUnflattenedList
+//
+
+import {input, templateCompositeFrom} from '#composite';
+import {isString, validateArrayItems} from '#validators';
+
+export default templateCompositeFrom({
+  annotation: `withPropertiesFromList`,
+
+  inputs: {
+    list: input({type: 'array'}),
+
+    properties: input({
+      validate: validateArrayItems(isString),
+    }),
+
+    prefix: input.staticValue({type: 'string', defaultValue: null}),
+  },
+
+  outputs: ({
+    [input.staticDependency('list')]: list,
+    [input.staticValue('properties')]: properties,
+    [input.staticValue('prefix')]: prefix,
+  }) =>
+    (properties
+      ? properties.map(property =>
+          (prefix
+            ? `${prefix}.${property}`
+         : list
+            ? `${list}.${property}`
+            : `#list.${property}`))
+      : ['#lists']),
+
+  steps: () => [
+    {
+      dependencies: [input('list'), input('properties')],
+      compute: (continuation, {
+        [input('list')]: list,
+        [input('properties')]: properties,
+      }) => continuation({
+        ['#lists']:
+          Object.fromEntries(
+            properties.map(property => [
+              property,
+              list.map(item => item[property] ?? null),
+            ])),
+      }),
+    },
+
+    {
+      dependencies: [
+        input.staticDependency('list'),
+        input.staticValue('properties'),
+        input.staticValue('prefix'),
+        '#lists',
+      ],
+
+      compute: (continuation, {
+        [input.staticDependency('list')]: list,
+        [input.staticValue('properties')]: properties,
+        [input.staticValue('prefix')]: prefix,
+        ['#lists']: lists,
+      }) =>
+        (properties
+          ? continuation(
+              Object.fromEntries(
+                properties.map(property => [
+                  (prefix
+                    ? `${prefix}.${property}`
+                 : list
+                    ? `${list}.${property}`
+                    : `#list.${property}`),
+                  lists[property],
+                ])))
+          : continuation({'#lists': lists})),
+    },
+  ],
+});
diff --git a/src/data/composite/data/withPropertiesFromObject.js b/src/data/composite/data/withPropertiesFromObject.js
new file mode 100644
index 00000000..21726b58
--- /dev/null
+++ b/src/data/composite/data/withPropertiesFromObject.js
@@ -0,0 +1,87 @@
+// Gets the listed properties from some object, providing each property's value
+// as a dependency prefixed with the same name as the object (by default).
+// If the object itself is null, all provided dependencies will be null;
+// if it's missing only select properties, those will be provided as null.
+//
+// See also:
+//  - withPropertiesFromList
+//  - withPropertyFromObject
+//
+
+import {input, templateCompositeFrom} from '#composite';
+import {isString, validateArrayItems} from '#validators';
+
+export default templateCompositeFrom({
+  annotation: `withPropertiesFromObject`,
+
+  inputs: {
+    object: input({type: 'object', acceptsNull: true}),
+
+    properties: input({
+      type: 'array',
+      validate: validateArrayItems(isString),
+    }),
+
+    prefix: input.staticValue({type: 'string', defaultValue: null}),
+  },
+
+  outputs: ({
+    [input.staticDependency('object')]: object,
+    [input.staticValue('properties')]: properties,
+    [input.staticValue('prefix')]: prefix,
+  }) =>
+    (properties
+      ? properties.map(property =>
+          (prefix
+            ? `${prefix}.${property}`
+         : object
+            ? `${object}.${property}`
+            : `#object.${property}`))
+      : ['#object']),
+
+  steps: () => [
+    {
+      dependencies: [input('object'), input('properties')],
+      compute: (continuation, {
+        [input('object')]: object,
+        [input('properties')]: properties,
+      }) => continuation({
+        ['#entries']:
+          (object === null
+            ? properties.map(property => [property, null])
+            : properties.map(property => [property, object[property]])),
+      }),
+    },
+
+    {
+      dependencies: [
+        input.staticDependency('object'),
+        input.staticValue('properties'),
+        input.staticValue('prefix'),
+        '#entries',
+      ],
+
+      compute: (continuation, {
+        [input.staticDependency('object')]: object,
+        [input.staticValue('properties')]: properties,
+        [input.staticValue('prefix')]: prefix,
+        ['#entries']: entries,
+      }) =>
+        (properties
+          ? continuation(
+              Object.fromEntries(
+                entries.map(([property, value]) => [
+                  (prefix
+                    ? `${prefix}.${property}`
+                 : object
+                    ? `${object}.${property}`
+                    : `#object.${property}`),
+                  value ?? null,
+                ])))
+          : continuation({
+              ['#object']:
+                Object.fromEntries(entries),
+            })),
+    },
+  ],
+});
diff --git a/src/data/composite/data/withPropertyFromList.js b/src/data/composite/data/withPropertyFromList.js
new file mode 100644
index 00000000..1983ebbc
--- /dev/null
+++ b/src/data/composite/data/withPropertyFromList.js
@@ -0,0 +1,82 @@
+// Gets a property from each of a list of objects (in a dependency) and
+// provides the results.
+//
+// This doesn't alter any list indices, so positions which were null in the
+// original list are kept null here. Objects which don't have the specified
+// property are retained in-place as null.
+//
+// See also:
+//  - withPropertiesFromList
+//  - withPropertyFromObject
+//
+// More list utilities:
+//  - excludeFromList
+//  - fillMissingListItems
+//  - withFlattenedList
+//  - withUnflattenedList
+//
+
+import {input, templateCompositeFrom} from '#composite';
+
+function getOutputName({list, property, prefix}) {
+  if (!property) return `#values`;
+  if (prefix) return `${prefix}.${property}`;
+  if (list) return `${list}.${property}`;
+  return `#list.${property}`;
+}
+
+export default templateCompositeFrom({
+  annotation: `withPropertyFromList`,
+
+  inputs: {
+    list: input({type: 'array'}),
+    property: input({type: 'string'}),
+    prefix: input.staticValue({type: 'string', defaultValue: null}),
+  },
+
+  outputs: ({
+    [input.staticDependency('list')]: list,
+    [input.staticValue('property')]: property,
+    [input.staticValue('prefix')]: prefix,
+  }) =>
+    [getOutputName({list, property, prefix})],
+
+  steps: () => [
+    {
+      dependencies: [input('list'), input('property')],
+      compute: (continuation, {
+        [input('list')]: list,
+        [input('property')]: property,
+      }) => continuation({
+        ['#values']:
+          list.map(item => item[property] ?? null),
+      }),
+    },
+
+    {
+      dependencies: [
+        input.staticDependency('list'),
+        input.staticValue('property'),
+        input.staticValue('prefix'),
+      ],
+
+      compute: (continuation, {
+        [input.staticDependency('list')]: list,
+        [input.staticValue('property')]: property,
+        [input.staticValue('prefix')]: prefix,
+      }) => continuation({
+        ['#outputName']:
+          getOutputName({list, property, prefix}),
+      }),
+    },
+
+    {
+      dependencies: ['#values', '#outputName'],
+      compute: (continuation, {
+        ['#values']: values,
+        ['#outputName']: outputName,
+      }) =>
+        continuation.raiseOutput({[outputName]: values}),
+    },
+  ],
+});
diff --git a/src/data/composite/data/withPropertyFromObject.js b/src/data/composite/data/withPropertyFromObject.js
new file mode 100644
index 00000000..b31bab15
--- /dev/null
+++ b/src/data/composite/data/withPropertyFromObject.js
@@ -0,0 +1,69 @@
+// Gets a property of some object (in a dependency) and provides that value.
+// If the object itself is null, or the object doesn't have the listed property,
+// the provided dependency will also be null.
+//
+// See also:
+//  - withPropertiesFromObject
+//  - withPropertyFromList
+//
+
+import {input, templateCompositeFrom} from '#composite';
+
+export default templateCompositeFrom({
+  annotation: `withPropertyFromObject`,
+
+  inputs: {
+    object: input({type: 'object', acceptsNull: true}),
+    property: input({type: 'string'}),
+  },
+
+  outputs: ({
+    [input.staticDependency('object')]: object,
+    [input.staticValue('property')]: property,
+  }) =>
+    (object && property
+      ? (object.startsWith('#')
+          ? [`${object}.${property}`]
+          : [`#${object}.${property}`])
+      : ['#value']),
+
+  steps: () => [
+    {
+      dependencies: [
+        input.staticDependency('object'),
+        input.staticValue('property'),
+      ],
+
+      compute: (continuation, {
+        [input.staticDependency('object')]: object,
+        [input.staticValue('property')]: property,
+      }) => continuation({
+        '#output':
+          (object && property
+            ? (object.startsWith('#')
+                ? `${object}.${property}`
+                : `#${object}.${property}`)
+            : '#value'),
+      }),
+    },
+
+    {
+      dependencies: [
+        '#output',
+        input('object'),
+        input('property'),
+      ],
+
+      compute: (continuation, {
+        ['#output']: output,
+        [input('object')]: object,
+        [input('property')]: property,
+      }) => continuation({
+        [output]:
+          (object === null
+            ? null
+            : object[property] ?? null),
+      }),
+    },
+  ],
+});
diff --git a/src/data/composite/data/withUnflattenedList.js b/src/data/composite/data/withUnflattenedList.js
new file mode 100644
index 00000000..3cfc247b
--- /dev/null
+++ b/src/data/composite/data/withUnflattenedList.js
@@ -0,0 +1,62 @@
+// After mapping the contents of a flattened array in-place (being careful to
+// retain the original indices by replacing unmatched results with null instead
+// of filtering them out), this function allows for recombining them. It will
+// filter out null and undefined items by default (pass {filter: false} to
+// disable this).
+
+import {input, templateCompositeFrom} from '#composite';
+import {isWholeNumber, validateArrayItems} from '#validators';
+
+export default templateCompositeFrom({
+  annotation: `withUnflattenedList`,
+
+  inputs: {
+    list: input({
+      type: 'array',
+      defaultDependency: '#flattenedList',
+    }),
+
+    indices: input({
+      validate: validateArrayItems(isWholeNumber),
+      defaultDependency: '#flattenedIndices',
+    }),
+
+    filter: input({
+      type: 'boolean',
+      defaultValue: true,
+    }),
+  },
+
+  outputs: ['#unflattenedList'],
+
+  steps: () => [
+    {
+      dependencies: [input('list'), input('indices'), input('filter')],
+      compute(continuation, {
+        [input('list')]: list,
+        [input('indices')]: indices,
+        [input('filter')]: filter,
+      }) {
+        const unflattenedList = [];
+
+        for (let i = 0; i < indices.length; i++) {
+          const startIndex = indices[i];
+          const endIndex =
+            (i === indices.length - 1
+              ? list.length
+              : indices[i + 1]);
+
+          const values = list.slice(startIndex, endIndex);
+          unflattenedList.push(
+            (filter
+              ? values.filter(value => value !== null && value !== undefined)
+              : values));
+        }
+
+        return continuation({
+          ['#unflattenedList']: unflattenedList,
+        });
+      },
+    },
+  ],
+});
diff --git a/src/data/composite/things/album/index.js b/src/data/composite/things/album/index.js
new file mode 100644
index 00000000..8139f10e
--- /dev/null
+++ b/src/data/composite/things/album/index.js
@@ -0,0 +1,2 @@
+export {default as withTracks} from './withTracks.js';
+export {default as withTrackSections} from './withTrackSections.js';
diff --git a/src/data/composite/things/album/withTrackSections.js b/src/data/composite/things/album/withTrackSections.js
new file mode 100644
index 00000000..baa3cb4a
--- /dev/null
+++ b/src/data/composite/things/album/withTrackSections.js
@@ -0,0 +1,128 @@
+import {input, templateCompositeFrom} from '#composite';
+import find from '#find';
+import {empty, stitchArrays} from '#sugar';
+import {isTrackSectionList} from '#validators';
+import {filterMultipleArrays} from '#wiki-data';
+
+import {exitWithoutDependency, exitWithoutUpdateValue}
+  from '#composite/control-flow';
+import {withResolvedReferenceList} from '#composite/wiki-data';
+
+import {
+  fillMissingListItems,
+  withFlattenedList,
+  withPropertiesFromList,
+  withUnflattenedList,
+} from '#composite/data';
+
+export default templateCompositeFrom({
+  annotation: `withTrackSections`,
+
+  outputs: ['#trackSections'],
+
+  steps: () => [
+    exitWithoutDependency({
+      dependency: 'trackData',
+      value: input.value([]),
+    }),
+
+    exitWithoutUpdateValue({
+      mode: input.value('empty'),
+      value: input.value([]),
+    }),
+
+    // TODO: input.updateValue description down here is a kludge.
+    withPropertiesFromList({
+      list: input.updateValue({
+        validate: isTrackSectionList,
+      }),
+      prefix: input.value('#sections'),
+      properties: input.value([
+        'tracks',
+        'dateOriginallyReleased',
+        'isDefaultTrackSection',
+        'name',
+        'color',
+      ]),
+    }),
+
+    fillMissingListItems({
+      list: '#sections.tracks',
+      fill: input.value([]),
+    }),
+
+    fillMissingListItems({
+      list: '#sections.isDefaultTrackSection',
+      fill: input.value(false),
+    }),
+
+    fillMissingListItems({
+      list: '#sections.name',
+      fill: input.value('Unnamed Track Section'),
+    }),
+
+    fillMissingListItems({
+      list: '#sections.color',
+      fill: input.dependency('color'),
+    }),
+
+    withFlattenedList({
+      list: '#sections.tracks',
+    }).outputs({
+      ['#flattenedList']: '#trackRefs',
+      ['#flattenedIndices']: '#sections.startIndex',
+    }),
+
+    withResolvedReferenceList({
+      list: '#trackRefs',
+      data: 'trackData',
+      notFoundMode: input.value('null'),
+      find: input.value(find.track),
+    }).outputs({
+      ['#resolvedReferenceList']: '#tracks',
+    }),
+
+    withUnflattenedList({
+      list: '#tracks',
+      indices: '#sections.startIndex',
+    }).outputs({
+      ['#unflattenedList']: '#sections.tracks',
+    }),
+
+    {
+      dependencies: [
+        '#sections.tracks',
+        '#sections.name',
+        '#sections.color',
+        '#sections.dateOriginallyReleased',
+        '#sections.isDefaultTrackSection',
+        '#sections.startIndex',
+      ],
+
+      compute: (continuation, {
+        '#sections.tracks': tracks,
+        '#sections.name': name,
+        '#sections.color': color,
+        '#sections.dateOriginallyReleased': dateOriginallyReleased,
+        '#sections.isDefaultTrackSection': isDefaultTrackSection,
+        '#sections.startIndex': startIndex,
+      }) => {
+        filterMultipleArrays(
+          tracks, name, color, dateOriginallyReleased, isDefaultTrackSection, startIndex,
+          tracks => !empty(tracks));
+
+        return continuation({
+          ['#trackSections']:
+            stitchArrays({
+              tracks,
+              name,
+              color,
+              dateOriginallyReleased,
+              isDefaultTrackSection,
+              startIndex,
+            }),
+        });
+      },
+    },
+  ],
+});
diff --git a/src/data/composite/things/album/withTracks.js b/src/data/composite/things/album/withTracks.js
new file mode 100644
index 00000000..dcea6593
--- /dev/null
+++ b/src/data/composite/things/album/withTracks.js
@@ -0,0 +1,51 @@
+import {input, templateCompositeFrom} from '#composite';
+import find from '#find';
+
+import {exitWithoutDependency, raiseOutputWithoutDependency}
+  from '#composite/control-flow';
+import {withResolvedReferenceList} from '#composite/wiki-data';
+
+export default templateCompositeFrom({
+  annotation: `withTracks`,
+
+  outputs: ['#tracks'],
+
+  steps: () => [
+    exitWithoutDependency({
+      dependency: 'trackData',
+      value: input.value([]),
+    }),
+
+    raiseOutputWithoutDependency({
+      dependency: 'trackSections',
+      mode: input.value('empty'),
+      output: input.value({
+        ['#tracks']: [],
+      }),
+    }),
+
+    {
+      dependencies: ['trackSections'],
+      compute: (continuation, {trackSections}) =>
+        continuation({
+          '#trackRefs': trackSections
+            .flatMap(section => section.tracks ?? []),
+        }),
+    },
+
+    withResolvedReferenceList({
+      list: '#trackRefs',
+      data: 'trackData',
+      find: input.value(find.track),
+    }),
+
+    {
+      dependencies: ['#resolvedReferenceList'],
+      compute: (continuation, {
+        ['#resolvedReferenceList']: resolvedReferenceList,
+      }) => continuation({
+        ['#tracks']: resolvedReferenceList,
+      })
+    },
+  ],
+});
diff --git a/src/data/composite/things/flash/index.js b/src/data/composite/things/flash/index.js
new file mode 100644
index 00000000..63ac13da
--- /dev/null
+++ b/src/data/composite/things/flash/index.js
@@ -0,0 +1 @@
+export {default as withFlashAct} from './withFlashAct.js';
diff --git a/src/data/composite/things/flash/withFlashAct.js b/src/data/composite/things/flash/withFlashAct.js
new file mode 100644
index 00000000..ada2dcfe
--- /dev/null
+++ b/src/data/composite/things/flash/withFlashAct.js
@@ -0,0 +1,108 @@
+// Gets the flash's act. This will early exit if flashActData is missing.
+// By default, if there's no flash whose list of flashes includes this flash,
+// the output dependency will be null; set {notFoundMode: 'exit'} to early
+// exit instead.
+//
+// This step models with Flash.withAlbum.
+
+import {input, templateCompositeFrom} from '#composite';
+import {is} from '#validators';
+
+import {exitWithoutDependency, withResultOfAvailabilityCheck}
+  from '#composite/control-flow';
+import {withPropertyFromList} from '#composite/data';
+
+export default templateCompositeFrom({
+  annotation: `withFlashAct`,
+
+  inputs: {
+    notFoundMode: input({
+      validate: is('exit', 'null'),
+      defaultValue: 'null',
+    }),
+  },
+
+  outputs: ['#flashAct'],
+
+  steps: () => [
+    // null flashActData is always an early exit.
+
+    exitWithoutDependency({
+      dependency: 'flashActData',
+      mode: input.value('null'),
+    }),
+
+    // empty flashActData conditionally exits early or outputs null.
+
+    withResultOfAvailabilityCheck({
+      from: 'flashActData',
+      mode: input.value('empty'),
+    }).outputs({
+      '#availability': '#flashActDataAvailability',
+    }),
+
+    {
+      dependencies: [input('notFoundMode'), '#flashActDataAvailability'],
+      compute(continuation, {
+        [input('notFoundMode')]: notFoundMode,
+        ['#flashActDataAvailability']: flashActDataIsAvailable,
+      }) {
+        if (flashActDataIsAvailable) return continuation();
+        switch (notFoundMode) {
+          case 'exit': return continuation.exit(null);
+          case 'null': return continuation.raiseOutput({'#flashAct': null});
+        }
+      },
+    },
+
+    withPropertyFromList({
+      list: 'flashActData',
+      property: input.value('flashes'),
+    }),
+
+    {
+      dependencies: [input.myself(), '#flashActData.flashes'],
+      compute: (continuation, {
+        [input.myself()]: track,
+        ['#flashActData.flashes']: flashLists,
+      }) => continuation({
+        ['#flashActIndex']:
+          flashLists.findIndex(flashes => flashes.includes(track)),
+      }),
+    },
+
+    // album not found conditionally exits or outputs null.
+
+    withResultOfAvailabilityCheck({
+      from: '#flashActIndex',
+      mode: input.value('index'),
+    }).outputs({
+      '#availability': '#flashActAvailability',
+    }),
+
+    {
+      dependencies: [input('notFoundMode'), '#flashActAvailability'],
+      compute(continuation, {
+        [input('notFoundMode')]: notFoundMode,
+        ['#flashActAvailability']: flashActIsAvailable,
+      }) {
+        if (flashActIsAvailable) return continuation();
+        switch (notFoundMode) {
+          case 'exit': return continuation.exit(null);
+          case 'null': return continuation.raiseOutput({'#flashAct': null});
+        }
+      },
+    },
+
+    {
+      dependencies: ['flashActData', '#flashActIndex'],
+      compute: (continuation, {
+        ['flashActData']: flashActData,
+        ['#flashActIndex']: flashActIndex,
+      }) => continuation.raiseOutput({
+        ['#flashAct']:
+          flashActData[flashActIndex],
+      }),
+    },
+  ],
+});
diff --git a/src/data/composite/things/track/exitWithoutUniqueCoverArt.js b/src/data/composite/things/track/exitWithoutUniqueCoverArt.js
new file mode 100644
index 00000000..f47086d9
--- /dev/null
+++ b/src/data/composite/things/track/exitWithoutUniqueCoverArt.js
@@ -0,0 +1,26 @@
+// Shorthand for checking if the track has unique cover art and exposing a
+// fallback value if it isn't.
+
+import {input, templateCompositeFrom} from '#composite';
+
+import {exitWithoutDependency} from '#composite/control-flow';
+
+import withHasUniqueCoverArt from './withHasUniqueCoverArt.js';
+
+export default templateCompositeFrom({
+  annotation: `exitWithoutUniqueCoverArt`,
+
+  inputs: {
+    value: input({defaultValue: null}),
+  },
+
+  steps: () => [
+    withHasUniqueCoverArt(),
+
+    exitWithoutDependency({
+      dependency: '#hasUniqueCoverArt',
+      mode: input.value('falsy'),
+      value: input('value'),
+    }),
+  ],
+});
diff --git a/src/data/composite/things/track/index.js b/src/data/composite/things/track/index.js
new file mode 100644
index 00000000..3354b1c4
--- /dev/null
+++ b/src/data/composite/things/track/index.js
@@ -0,0 +1,9 @@
+export {default as exitWithoutUniqueCoverArt} from './exitWithoutUniqueCoverArt.js';
+export {default as inheritFromOriginalRelease} from './inheritFromOriginalRelease.js';
+export {default as trackReverseReferenceList} from './trackReverseReferenceList.js';
+export {default as withAlbum} from './withAlbum.js';
+export {default as withAlwaysReferenceByDirectory} from './withAlwaysReferenceByDirectory.js';
+export {default as withContainingTrackSection} from './withContainingTrackSection.js';
+export {default as withHasUniqueCoverArt} from './withHasUniqueCoverArt.js';
+export {default as withOtherReleases} from './withOtherReleases.js';
+export {default as withPropertyFromAlbum} from './withPropertyFromAlbum.js';
diff --git a/src/data/composite/things/track/inheritFromOriginalRelease.js b/src/data/composite/things/track/inheritFromOriginalRelease.js
new file mode 100644
index 00000000..a9d57f86
--- /dev/null
+++ b/src/data/composite/things/track/inheritFromOriginalRelease.js
@@ -0,0 +1,43 @@
+// Early exits with a value inherited from the original release, if
+// this track is a rerelease, and otherwise continues with no further
+// dependencies provided. If allowOverride is true, then the continuation
+// will also be called if the original release exposed the requested
+// property as null.
+
+import {input, templateCompositeFrom} from '#composite';
+
+import withOriginalRelease from './withOriginalRelease.js';
+
+export default templateCompositeFrom({
+  annotation: `inheritFromOriginalRelease`,
+
+  inputs: {
+    property: input({type: 'string'}),
+    allowOverride: input({type: 'boolean', defaultValue: false}),
+  },
+
+  steps: () => [
+    withOriginalRelease(),
+
+    {
+      dependencies: [
+        '#originalRelease',
+        input('property'),
+        input('allowOverride'),
+      ],
+
+      compute: (continuation, {
+        ['#originalRelease']: originalRelease,
+        [input('property')]: originalProperty,
+        [input('allowOverride')]: allowOverride,
+      }) => {
+        if (!originalRelease) return continuation();
+
+        const value = originalRelease[originalProperty];
+        if (allowOverride && value === null) return continuation();
+
+        return continuation.exit(value);
+      },
+    },
+  ],
+});
diff --git a/src/data/composite/things/track/trackReverseReferenceList.js b/src/data/composite/things/track/trackReverseReferenceList.js
new file mode 100644
index 00000000..e7bfedf3
--- /dev/null
+++ b/src/data/composite/things/track/trackReverseReferenceList.js
@@ -0,0 +1,38 @@
+// Like a normal reverse reference list ("objects which reference this object
+// under a specified property"), only excluding re-releases from the possible
+// outputs. While it's useful to travel from a re-release to the tracks it
+// references, re-releases aren't generally relevant from the perspective of
+// the tracks *being* referenced. Apart from hiding re-releases from lists on
+// the site, it also excludes keeps them from relational data processing, such
+// as on the "Tracks - by Times Referenced" listing page.
+
+import {input, templateCompositeFrom} from '#composite';
+import {withReverseReferenceList} from '#composite/wiki-data';
+
+export default templateCompositeFrom({
+  annotation: `trackReverseReferenceList`,
+
+  compose: false,
+
+  inputs: {
+    list: input({type: 'string'}),
+  },
+
+  steps: () => [
+    withReverseReferenceList({
+      data: 'trackData',
+      list: input('list'),
+    }),
+
+    {
+      flags: {expose: true},
+      expose: {
+        dependencies: ['#reverseReferenceList'],
+        compute: ({
+          ['#reverseReferenceList']: reverseReferenceList,
+        }) =>
+          reverseReferenceList.filter(track => !track.originalReleaseTrack),
+      },
+    },
+  ],
+});
diff --git a/src/data/composite/things/track/withAlbum.js b/src/data/composite/things/track/withAlbum.js
new file mode 100644
index 00000000..cbd16dcd
--- /dev/null
+++ b/src/data/composite/things/track/withAlbum.js
@@ -0,0 +1,108 @@
+// Gets the track's album. This will early exit if albumData is missing.
+// By default, if there's no album whose list of tracks includes this track,
+// the output dependency will be null; set {notFoundMode: 'exit'} to early
+// exit instead.
+//
+// This step models with Flash.withFlashAct.
+
+import {input, templateCompositeFrom} from '#composite';
+import {is} from '#validators';
+
+import {exitWithoutDependency, withResultOfAvailabilityCheck}
+  from '#composite/control-flow';
+import {withPropertyFromList} from '#composite/data';
+
+export default templateCompositeFrom({
+  annotation: `withAlbum`,
+
+  inputs: {
+    notFoundMode: input({
+      validate: is('exit', 'null'),
+      defaultValue: 'null',
+    }),
+  },
+
+  outputs: ['#album'],
+
+  steps: () => [
+    // null albumData is always an early exit.
+
+    exitWithoutDependency({
+      dependency: 'albumData',
+      mode: input.value('null'),
+    }),
+
+    // empty albumData conditionally exits early or outputs null.
+
+    withResultOfAvailabilityCheck({
+      from: 'albumData',
+      mode: input.value('empty'),
+    }).outputs({
+      '#availability': '#albumDataAvailability',
+    }),
+
+    {
+      dependencies: [input('notFoundMode'), '#albumDataAvailability'],
+      compute(continuation, {
+        [input('notFoundMode')]: notFoundMode,
+        ['#albumDataAvailability']: albumDataIsAvailable,
+      }) {
+        if (albumDataIsAvailable) return continuation();
+        switch (notFoundMode) {
+          case 'exit': return continuation.exit(null);
+          case 'null': return continuation.raiseOutput({'#album': null});
+        }
+      },
+    },
+
+    withPropertyFromList({
+      list: 'albumData',
+      property: input.value('tracks'),
+    }),
+
+    {
+      dependencies: [input.myself(), '#albumData.tracks'],
+      compute: (continuation, {
+        [input.myself()]: track,
+        ['#albumData.tracks']: trackLists,
+      }) => continuation({
+        ['#albumIndex']:
+          trackLists.findIndex(tracks => tracks.includes(track)),
+      }),
+    },
+
+    // album not found conditionally exits or outputs null.
+
+    withResultOfAvailabilityCheck({
+      from: '#albumIndex',
+      mode: input.value('index'),
+    }).outputs({
+      '#availability': '#albumAvailability',
+    }),
+
+    {
+      dependencies: [input('notFoundMode'), '#albumAvailability'],
+      compute(continuation, {
+        [input('notFoundMode')]: notFoundMode,
+        ['#albumAvailability']: albumIsAvailable,
+      }) {
+        if (albumIsAvailable) return continuation();
+        switch (notFoundMode) {
+          case 'exit': return continuation.exit(null);
+          case 'null': return continuation.raiseOutput({'#album': null});
+        }
+      },
+    },
+
+    {
+      dependencies: ['albumData', '#albumIndex'],
+      compute: (continuation, {
+        ['albumData']: albumData,
+        ['#albumIndex']: albumIndex,
+      }) => continuation.raiseOutput({
+        ['#album']:
+          albumData[albumIndex],
+      }),
+    },
+  ],
+});
diff --git a/src/data/composite/things/track/withAlwaysReferenceByDirectory.js b/src/data/composite/things/track/withAlwaysReferenceByDirectory.js
new file mode 100644
index 00000000..d27f7b23
--- /dev/null
+++ b/src/data/composite/things/track/withAlwaysReferenceByDirectory.js
@@ -0,0 +1,91 @@
+// Controls how find.track works - it'll never be matched by a reference
+// just to the track's name, which means you don't have to always reference
+// some *other* (much more commonly referenced) track by directory instead
+// of more naturally by name.
+//
+// See the implementation for an important caveat about matching the original
+// track against other tracks, which uses a custom implementation pulling (and
+// duplicating) details from #find instead of using withOriginalRelease and the
+// usual withResolvedReference / find.track() utilities.
+//
+
+import {input, templateCompositeFrom} from '#composite';
+import {isBoolean} from '#validators';
+
+import {exitWithoutDependency, exposeUpdateValueOrContinue}
+  from '#composite/control-flow';
+import {withPropertyFromObject} from '#composite/data';
+
+// TODO: Kludge. (The usage of this, not so much the import.)
+import CacheableObject from '../../../things/cacheable-object.js';
+
+export default templateCompositeFrom({
+  annotation: `withAlwaysReferenceByDirectory`,
+
+  outputs: ['#alwaysReferenceByDirectory'],
+
+  steps: () => [
+    exposeUpdateValueOrContinue({
+      validate: input.value(isBoolean),
+    }),
+
+    // Remaining code is for defaulting to true if this track is a rerelease of
+    // another with the same name, so everything further depends on access to
+    // trackData as well as originalReleaseTrack.
+
+    exitWithoutDependency({
+      dependency: 'trackData',
+      mode: input.value('empty'),
+      value: input.value(false),
+    }),
+
+    exitWithoutDependency({
+      dependency: 'originalReleaseTrack',
+      value: input.value(false),
+    }),
+
+    // "Slow" / uncached, manual search from trackData (with this track
+    // excluded). Otherwise there end up being pretty bad recursion issues
+    // (track1.alwaysReferencedByDirectory depends on searching through data
+    // including track2, which depends on evaluating track2.alwaysReferenced-
+    // ByDirectory, which depends on searcing through data including track1...)
+    // That said, this is 100% a kludge, since it involves duplicating find
+    // logic on a completely unrelated context.
+    {
+      dependencies: [input.myself(), 'trackData', 'originalReleaseTrack'],
+      compute: (continuation, {
+        [input.myself()]: thisTrack,
+        ['trackData']: trackData,
+        ['originalReleaseTrack']: ref,
+      }) => continuation({
+        ['#originalRelease']:
+          (ref.startsWith('track:')
+            ? trackData.find(track => track.directory === ref.slice('track:'.length))
+            : trackData.find(track =>
+                track !== thisTrack &&
+                !CacheableObject.getUpdateValue(track, 'originalReleaseTrack') &&
+                track.name.toLowerCase() === ref.toLowerCase())),
+      })
+    },
+
+    exitWithoutDependency({
+      dependency: '#originalRelease',
+      value: input.value(false),
+    }),
+
+    withPropertyFromObject({
+      object: '#originalRelease',
+      property: input.value('name'),
+    }),
+
+    {
+      dependencies: ['name', '#originalRelease.name'],
+      compute: (continuation, {
+        name,
+        ['#originalRelease.name']: originalName,
+      }) => continuation({
+        ['#alwaysReferenceByDirectory']: name === originalName,
+      }),
+    },
+  ],
+});
diff --git a/src/data/composite/things/track/withContainingTrackSection.js b/src/data/composite/things/track/withContainingTrackSection.js
new file mode 100644
index 00000000..b2e5f2b3
--- /dev/null
+++ b/src/data/composite/things/track/withContainingTrackSection.js
@@ -0,0 +1,63 @@
+// Gets the track section containing this track from its album's track list.
+// If notFoundMode is set to 'exit', this will early exit if the album can't be
+// found or if none of its trackSections includes the track for some reason.
+
+import {input, templateCompositeFrom} from '#composite';
+import {is} from '#validators';
+
+import withPropertyFromAlbum from './withPropertyFromAlbum.js';
+
+export default templateCompositeFrom({
+  annotation: `withContainingTrackSection`,
+
+  inputs: {
+    notFoundMode: input({
+      validate: is('exit', 'null'),
+      defaultValue: 'null',
+    }),
+  },
+
+  outputs: ['#trackSection'],
+
+  steps: () => [
+    withPropertyFromAlbum({
+      property: input.value('trackSections'),
+      notFoundMode: input('notFoundMode'),
+    }),
+
+    {
+      dependencies: [
+        input.myself(),
+        input('notFoundMode'),
+        '#album.trackSections',
+      ],
+
+      compute(continuation, {
+        [input.myself()]: track,
+        [input('notFoundMode')]: notFoundMode,
+        ['#album.trackSections']: trackSections,
+      }) {
+        if (!trackSections) {
+          return continuation.raiseOutput({
+            ['#trackSection']: null,
+          });
+        }
+
+        const trackSection =
+          trackSections.find(({tracks}) => tracks.includes(track));
+
+        if (trackSection) {
+          return continuation.raiseOutput({
+            ['#trackSection']: trackSection,
+          });
+        } else if (notFoundMode === 'exit') {
+          return continuation.exit(null);
+        } else {
+          return continuation.raiseOutput({
+            ['#trackSection']: null,
+          });
+        }
+      },
+    },
+  ],
+});
diff --git a/src/data/composite/things/track/withHasUniqueCoverArt.js b/src/data/composite/things/track/withHasUniqueCoverArt.js
new file mode 100644
index 00000000..96078d5f
--- /dev/null
+++ b/src/data/composite/things/track/withHasUniqueCoverArt.js
@@ -0,0 +1,61 @@
+// Whether or not the track has "unique" cover artwork - a cover which is
+// specifically associated with this track in particular, rather than with
+// the track's album as a whole. This is typically used to select between
+// displaying the track artwork and a fallback, such as the album artwork
+// or a placeholder. (This property is named hasUniqueCoverArt instead of
+// the usual hasCoverArt to emphasize that it does not inherit from the
+// album.)
+
+import {input, templateCompositeFrom} from '#composite';
+import {empty} from '#sugar';
+
+import {withResolvedContribs} from '#composite/wiki-data';
+
+import withPropertyFromAlbum from './withPropertyFromAlbum.js';
+
+export default templateCompositeFrom({
+  annotation: 'withHasUniqueCoverArt',
+
+  outputs: ['#hasUniqueCoverArt'],
+
+  steps: () => [
+    {
+      dependencies: ['disableUniqueCoverArt'],
+      compute: (continuation, {disableUniqueCoverArt}) =>
+        (disableUniqueCoverArt
+          ? continuation.raiseOutput({
+              ['#hasUniqueCoverArt']: false,
+            })
+          : continuation()),
+    },
+
+    withResolvedContribs({from: 'coverArtistContribs'}),
+
+    {
+      dependencies: ['#resolvedContribs'],
+      compute: (continuation, {
+        ['#resolvedContribs']: contribsFromTrack,
+      }) =>
+        (empty(contribsFromTrack)
+          ? continuation()
+          : continuation.raiseOutput({
+              ['#hasUniqueCoverArt']: true,
+            })),
+    },
+
+    withPropertyFromAlbum({
+      property: input.value('trackCoverArtistContribs'),
+    }),
+
+    {
+      dependencies: ['#album.trackCoverArtistContribs'],
+      compute: (continuation, {
+        ['#album.trackCoverArtistContribs']: contribsFromAlbum,
+      }) =>
+        continuation.raiseOutput({
+          ['#hasUniqueCoverArt']:
+            !empty(contribsFromAlbum),
+        }),
+    },
+  ],
+});
diff --git a/src/data/composite/things/track/withOriginalRelease.js b/src/data/composite/things/track/withOriginalRelease.js
new file mode 100644
index 00000000..d2ee39df
--- /dev/null
+++ b/src/data/composite/things/track/withOriginalRelease.js
@@ -0,0 +1,59 @@
+// Just includes the original release of this track as a dependency.
+// If this track isn't a rerelease, then it'll provide null, unless the
+// {selfIfOriginal} option is set, in which case it'll provide this track
+// itself. Note that this will early exit if the original release is
+// specified by reference and that reference doesn't resolve to anything.
+// Outputs to '#originalRelease' by default.
+
+import {input, templateCompositeFrom} from '#composite';
+import find from '#find';
+import {validateWikiData} from '#validators';
+
+import {withResolvedReference} from '#composite/wiki-data';
+
+export default templateCompositeFrom({
+  annotation: `withOriginalRelease`,
+
+  inputs: {
+    selfIfOriginal: input({type: 'boolean', defaultValue: false}),
+
+    data: input({
+      validate: validateWikiData({referenceType: 'track'}),
+      defaultDependency: 'trackData',
+    }),
+  },
+
+  outputs: ['#originalRelease'],
+
+  steps: () => [
+    withResolvedReference({
+      ref: 'originalReleaseTrack',
+      data: input('data'),
+      find: input.value(find.track),
+      notFoundMode: input.value('exit'),
+    }).outputs({
+      ['#resolvedReference']: '#originalRelease',
+    }),
+
+    {
+      dependencies: [
+        input.myself(),
+        input('selfIfOriginal'),
+        '#originalRelease',
+      ],
+
+      compute: (continuation, {
+        [input.myself()]: track,
+        [input('selfIfOriginal')]: selfIfOriginal,
+        ['#originalRelease']: originalRelease,
+      }) =>
+        continuation({
+          ['#originalRelease']:
+            (originalRelease ??
+              (selfIfOriginal
+                ? track
+                : null)),
+        }),
+    },
+  ],
+});
diff --git a/src/data/composite/things/track/withOtherReleases.js b/src/data/composite/things/track/withOtherReleases.js
new file mode 100644
index 00000000..84420cf8
--- /dev/null
+++ b/src/data/composite/things/track/withOtherReleases.js
@@ -0,0 +1,40 @@
+import {input, templateCompositeFrom} from '#composite';
+
+import {exitWithoutDependency} from '#composite/control-flow';
+
+import withOriginalRelease from './withOriginalRelease.js';
+
+export default templateCompositeFrom({
+  annotation: `withOtherReleases`,
+
+  outputs: ['#otherReleases'],
+
+  steps: () => [
+    exitWithoutDependency({
+      dependency: 'trackData',
+      mode: input.value('empty'),
+    }),
+
+    withOriginalRelease({
+      selfIfOriginal: input.value(true),
+    }),
+
+    {
+      dependencies: [input.myself(), '#originalRelease', 'trackData'],
+      compute: (continuation, {
+        [input.myself()]: thisTrack,
+        ['#originalRelease']: originalRelease,
+        trackData,
+      }) => continuation({
+        ['#otherReleases']:
+          (originalRelease === thisTrack
+            ? []
+            : [originalRelease])
+            .concat(trackData.filter(track =>
+              track !== originalRelease &&
+              track !== thisTrack &&
+              track.originalReleaseTrack === originalRelease)),
+      }),
+    },
+  ],
+});
diff --git a/src/data/composite/things/track/withPropertyFromAlbum.js b/src/data/composite/things/track/withPropertyFromAlbum.js
new file mode 100644
index 00000000..b236a6e8
--- /dev/null
+++ b/src/data/composite/things/track/withPropertyFromAlbum.js
@@ -0,0 +1,49 @@
+// Gets a single property from this track's album, providing it as the same
+// property name prefixed with '#album.' (by default). If the track's album
+// isn't available, then by default, the property will be provided as null;
+// set {notFoundMode: 'exit'} to early exit instead.
+
+import {input, templateCompositeFrom} from '#composite';
+import {is} from '#validators';
+
+import {withPropertyFromObject} from '#composite/data';
+
+import withAlbum from './withAlbum.js';
+
+export default templateCompositeFrom({
+  annotation: `withPropertyFromAlbum`,
+
+  inputs: {
+    property: input.staticValue({type: 'string'}),
+
+    notFoundMode: input({
+      validate: is('exit', 'null'),
+      defaultValue: 'null',
+    }),
+  },
+
+  outputs: ({
+    [input.staticValue('property')]: property,
+  }) => ['#album.' + property],
+
+  steps: () => [
+    withAlbum({
+      notFoundMode: input('notFoundMode'),
+    }),
+
+    withPropertyFromObject({
+      object: '#album',
+      property: input('property'),
+    }),
+
+    {
+      dependencies: ['#value', input.staticValue('property')],
+      compute: (continuation, {
+        ['#value']: value,
+        [input.staticValue('property')]: property,
+      }) => continuation({
+        ['#album.' + property]: value,
+      }),
+    },
+  ],
+});
diff --git a/src/data/composite/wiki-data/exitWithoutContribs.js b/src/data/composite/wiki-data/exitWithoutContribs.js
new file mode 100644
index 00000000..2c8219fc
--- /dev/null
+++ b/src/data/composite/wiki-data/exitWithoutContribs.js
@@ -0,0 +1,47 @@
+// Shorthand for exiting if the contribution list (usually a property's update
+// value) resolves to empty - ensuring that the later computed results are only
+// returned if these contributions are present.
+
+import {input, templateCompositeFrom} from '#composite';
+import {isContributionList} from '#validators';
+
+import {withResultOfAvailabilityCheck} from '#composite/control-flow';
+
+import withResolvedContribs from './withResolvedContribs.js';
+
+export default templateCompositeFrom({
+  annotation: `exitWithoutContribs`,
+
+  inputs: {
+    contribs: input({
+      validate: isContributionList,
+      acceptsNull: true,
+    }),
+
+    value: input({defaultValue: null}),
+  },
+
+  steps: () => [
+    withResolvedContribs({
+      from: input('contribs'),
+    }),
+
+    // TODO: Fairly certain exitWithoutDependency would be sufficient here.
+
+    withResultOfAvailabilityCheck({
+      from: '#resolvedContribs',
+      mode: input.value('empty'),
+    }),
+
+    {
+      dependencies: ['#availability', input('value')],
+      compute: (continuation, {
+        ['#availability']: availability,
+        [input('value')]: value,
+      }) =>
+        (availability
+          ? continuation()
+          : continuation.exit(value)),
+    },
+  ],
+});
diff --git a/src/data/composite/wiki-data/index.js b/src/data/composite/wiki-data/index.js
new file mode 100644
index 00000000..1d0400fc
--- /dev/null
+++ b/src/data/composite/wiki-data/index.js
@@ -0,0 +1,7 @@
+export {default as exitWithoutContribs} from './exitWithoutContribs.js';
+export {default as inputThingClass} from './inputThingClass.js';
+export {default as inputWikiData} from './inputWikiData.js';
+export {default as withResolvedContribs} from './withResolvedContribs.js';
+export {default as withResolvedReference} from './withResolvedReference.js';
+export {default as withResolvedReferenceList} from './withResolvedReferenceList.js';
+export {default as withReverseReferenceList} from './withReverseReferenceList.js';
diff --git a/src/data/composite/wiki-data/inputThingClass.js b/src/data/composite/wiki-data/inputThingClass.js
new file mode 100644
index 00000000..d70480e6
--- /dev/null
+++ b/src/data/composite/wiki-data/inputThingClass.js
@@ -0,0 +1,23 @@
+// Please note that this input, used in a variety of #composite/wiki-data
+// utilities, is basically always a kludge. Any usage of it depends on
+// referencing Thing class values defined outside of the #composite folder.
+
+import {input} from '#composite';
+import {isType} from '#validators';
+
+// TODO: Kludge.
+import Thing from '../../things/thing.js';
+
+export default function inputThingClass() {
+  return input.staticValue({
+    validate(thingClass) {
+      isType(thingClass, 'function');
+
+      if (!Object.hasOwn(thingClass, Thing.referenceType)) {
+        throw new TypeError(`Expected a Thing constructor, missing Thing.referenceType`);
+      }
+
+      return true;
+    },
+  });
+}
diff --git a/src/data/composite/wiki-data/inputWikiData.js b/src/data/composite/wiki-data/inputWikiData.js
new file mode 100644
index 00000000..cf7a7c2c
--- /dev/null
+++ b/src/data/composite/wiki-data/inputWikiData.js
@@ -0,0 +1,17 @@
+import {input} from '#composite';
+import {validateWikiData} from '#validators';
+
+// TODO: This doesn't access a class's own ThingSubclass[Thing.referenceType]
+// value because classes aren't initialized by when templateCompositeFrom gets
+// called (see: circular imports). So the reference types have to be hard-coded,
+// which somewhat defeats the point of storing them on the class in the first
+// place...
+export default function inputWikiData({
+  referenceType = '',
+  allowMixedTypes = false,
+} = {}) {
+  return input({
+    validate: validateWikiData({referenceType, allowMixedTypes}),
+    acceptsNull: true,
+  });
+}
diff --git a/src/data/composite/wiki-data/withResolvedContribs.js b/src/data/composite/wiki-data/withResolvedContribs.js
new file mode 100644
index 00000000..eda24160
--- /dev/null
+++ b/src/data/composite/wiki-data/withResolvedContribs.js
@@ -0,0 +1,77 @@
+// Resolves the contribsByRef contained in the provided dependency,
+// providing (named by the second argument) the result. "Resolving"
+// means mapping the "who" reference of each contribution to an artist
+// object, and filtering out those whose "who" doesn't match any artist.
+
+import {input, templateCompositeFrom} from '#composite';
+import find from '#find';
+import {stitchArrays} from '#sugar';
+import {is, isContributionList} from '#validators';
+import {filterMultipleArrays} from '#wiki-data';
+
+import {
+  raiseOutputWithoutDependency,
+} from '#composite/control-flow';
+
+import {
+  withPropertiesFromList,
+} from '#composite/data';
+
+import withResolvedReferenceList from './withResolvedReferenceList.js';
+
+export default templateCompositeFrom({
+  annotation: `withResolvedContribs`,
+
+  inputs: {
+    from: input({
+      validate: isContributionList,
+      acceptsNull: true,
+    }),
+
+    notFoundMode: input({
+      validate: is('exit', 'filter', 'null'),
+      defaultValue: 'null',
+    }),
+  },
+
+  outputs: ['#resolvedContribs'],
+
+  steps: () => [
+    raiseOutputWithoutDependency({
+      dependency: input('from'),
+      mode: input.value('empty'),
+      output: input.value({
+        ['#resolvedContribs']: [],
+      }),
+    }),
+
+    withPropertiesFromList({
+      list: input('from'),
+      properties: input.value(['who', 'what']),
+      prefix: input.value('#contribs'),
+    }),
+
+    withResolvedReferenceList({
+      list: '#contribs.who',
+      data: 'artistData',
+      find: input.value(find.artist),
+      notFoundMode: input('notFoundMode'),
+    }).outputs({
+      ['#resolvedReferenceList']: '#contribs.who',
+    }),
+
+    {
+      dependencies: ['#contribs.who', '#contribs.what'],
+
+      compute(continuation, {
+        ['#contribs.who']: who,
+        ['#contribs.what']: what,
+      }) {
+        filterMultipleArrays(who, what, (who, _what) => who);
+        return continuation({
+          ['#resolvedContribs']: stitchArrays({who, what}),
+        });
+      },
+    },
+  ],
+});
diff --git a/src/data/composite/wiki-data/withResolvedReference.js b/src/data/composite/wiki-data/withResolvedReference.js
new file mode 100644
index 00000000..0fa5c554
--- /dev/null
+++ b/src/data/composite/wiki-data/withResolvedReference.js
@@ -0,0 +1,73 @@
+// Resolves a reference by using the provided find function to match it
+// within the provided thingData dependency. This will early exit if the
+// data dependency is null, or, if notFoundMode is set to 'exit', if the find
+// function doesn't match anything for the reference. Otherwise, the data
+// object is provided on the output dependency; or null, if the reference
+// doesn't match anything or itself was null to begin with.
+
+import {input, templateCompositeFrom} from '#composite';
+import {is} from '#validators';
+
+import {
+  exitWithoutDependency,
+  raiseOutputWithoutDependency,
+} from '#composite/control-flow';
+
+import inputWikiData from './inputWikiData.js';
+
+export default templateCompositeFrom({
+  annotation: `withResolvedReference`,
+
+  inputs: {
+    ref: input({type: 'string', acceptsNull: true}),
+
+    data: inputWikiData({allowMixedTypes: false}),
+    find: input({type: 'function'}),
+
+    notFoundMode: input({
+      validate: is('null', 'exit'),
+      defaultValue: 'null',
+    }),
+  },
+
+  outputs: ['#resolvedReference'],
+
+  steps: () => [
+    raiseOutputWithoutDependency({
+      dependency: input('ref'),
+      output: input.value({
+        ['#resolvedReference']: null,
+      }),
+    }),
+
+    exitWithoutDependency({
+      dependency: input('data'),
+    }),
+
+    {
+      dependencies: [
+        input('ref'),
+        input('data'),
+        input('find'),
+        input('notFoundMode'),
+      ],
+
+      compute(continuation, {
+        [input('ref')]: ref,
+        [input('data')]: data,
+        [input('find')]: findFunction,
+        [input('notFoundMode')]: notFoundMode,
+      }) {
+        const match = findFunction(ref, data, {mode: 'quiet'});
+
+        if (match === null && notFoundMode === 'exit') {
+          return continuation.exit(null);
+        }
+
+        return continuation.raiseOutput({
+          ['#resolvedReference']: match ?? null,
+        });
+      },
+    },
+  ],
+});
diff --git a/src/data/composite/wiki-data/withResolvedReferenceList.js b/src/data/composite/wiki-data/withResolvedReferenceList.js
new file mode 100644
index 00000000..1d39e5b2
--- /dev/null
+++ b/src/data/composite/wiki-data/withResolvedReferenceList.js
@@ -0,0 +1,101 @@
+// Resolves a list of references, with each reference matched with provided
+// data in the same way as withResolvedReference. This will early exit if the
+// data dependency is null (even if the reference list is empty). By default
+// it will filter out references which don't match, but this can be changed
+// to early exit ({notFoundMode: 'exit'}) or leave null in place ('null').
+
+import {input, templateCompositeFrom} from '#composite';
+import {is, isString, validateArrayItems} from '#validators';
+
+import {
+  exitWithoutDependency,
+  raiseOutputWithoutDependency,
+} from '#composite/control-flow';
+
+import inputWikiData from './inputWikiData.js';
+
+export default templateCompositeFrom({
+  annotation: `withResolvedReferenceList`,
+
+  inputs: {
+    list: input({
+      validate: validateArrayItems(isString),
+      acceptsNull: true,
+    }),
+
+    data: inputWikiData({allowMixedTypes: false}),
+    find: input({type: 'function'}),
+
+    notFoundMode: input({
+      validate: is('exit', 'filter', 'null'),
+      defaultValue: 'filter',
+    }),
+  },
+
+  outputs: ['#resolvedReferenceList'],
+
+  steps: () => [
+    exitWithoutDependency({
+      dependency: input('data'),
+      value: input.value([]),
+    }),
+
+    raiseOutputWithoutDependency({
+      dependency: input('list'),
+      mode: input.value('empty'),
+      output: input.value({
+        ['#resolvedReferenceList']: [],
+      }),
+    }),
+
+    {
+      dependencies: [input('list'), input('data'), input('find')],
+      compute: (continuation, {
+        [input('list')]: list,
+        [input('data')]: data,
+        [input('find')]: findFunction,
+      }) =>
+        continuation({
+          '#matches': list.map(ref => findFunction(ref, data, {mode: 'quiet'})),
+        }),
+    },
+
+    {
+      dependencies: ['#matches'],
+      compute: (continuation, {'#matches': matches}) =>
+        (matches.every(match => match)
+          ? continuation.raiseOutput({
+              ['#resolvedReferenceList']: matches,
+            })
+          : continuation()),
+    },
+
+    {
+      dependencies: ['#matches', input('notFoundMode')],
+      compute(continuation, {
+        ['#matches']: matches,
+        [input('notFoundMode')]: notFoundMode,
+      }) {
+        switch (notFoundMode) {
+          case 'exit':
+            return continuation.exit([]);
+
+          case 'filter':
+            return continuation.raiseOutput({
+              ['#resolvedReferenceList']:
+                matches.filter(match => match),
+            });
+
+          case 'null':
+            return continuation.raiseOutput({
+              ['#resolvedReferenceList']:
+                matches.map(match => match ?? null),
+            });
+
+          default:
+            throw new TypeError(`Expected notFoundMode to be exit, filter, or null`);
+        }
+      },
+    },
+  ],
+});
diff --git a/src/data/composite/wiki-data/withReverseReferenceList.js b/src/data/composite/wiki-data/withReverseReferenceList.js
new file mode 100644
index 00000000..a025b5ed
--- /dev/null
+++ b/src/data/composite/wiki-data/withReverseReferenceList.js
@@ -0,0 +1,41 @@
+// Check out the info on reverseReferenceList!
+// This is its composable form.
+
+import {input, templateCompositeFrom} from '#composite';
+
+import {exitWithoutDependency} from '#composite/control-flow';
+
+import inputWikiData from './inputWikiData.js';
+
+export default templateCompositeFrom({
+  annotation: `withReverseReferenceList`,
+
+  inputs: {
+    data: inputWikiData({allowMixedTypes: false}),
+    list: input({type: 'string'}),
+  },
+
+  outputs: ['#reverseReferenceList'],
+
+  steps: () => [
+    exitWithoutDependency({
+      dependency: input('data'),
+      value: input.value([]),
+      mode: input.value('empty'),
+    }),
+
+    {
+      dependencies: [input.myself(), input('data'), input('list')],
+
+      compute: (continuation, {
+        [input.myself()]: thisThing,
+        [input('data')]: data,
+        [input('list')]: refListProperty,
+      }) =>
+        continuation({
+          ['#reverseReferenceList']:
+            data.filter(thing => thing[refListProperty].includes(thisThing)),
+        }),
+    },
+  ],
+});
diff --git a/src/data/composite/wiki-properties/additionalFiles.js b/src/data/composite/wiki-properties/additionalFiles.js
new file mode 100644
index 00000000..6760527a
--- /dev/null
+++ b/src/data/composite/wiki-properties/additionalFiles.js
@@ -0,0 +1,30 @@
+// This is a somewhat more involved data structure - it's for additional
+// or "bonus" files associated with albums or tracks (or anything else).
+// It's got this form:
+//
+//   [
+//     {title: 'Booklet', files: ['Booklet.pdf']},
+//     {
+//       title: 'Wallpaper',
+//       description: 'Cool Wallpaper!',
+//       files: ['1440x900.png', '1920x1080.png']
+//     },
+//     {title: 'Alternate Covers', description: null, files: [...]},
+//     ...
+//   ]
+//
+
+import {isAdditionalFileList} from '#validators';
+
+// TODO: Not templateCompositeFrom.
+
+export default function() {
+  return {
+    flags: {update: true, expose: true},
+    update: {validate: isAdditionalFileList},
+    expose: {
+      transform: (additionalFiles) =>
+        additionalFiles ?? [],
+    },
+  };
+}
diff --git a/src/data/composite/wiki-properties/color.js b/src/data/composite/wiki-properties/color.js
new file mode 100644
index 00000000..1bc9888b
--- /dev/null
+++ b/src/data/composite/wiki-properties/color.js
@@ -0,0 +1,12 @@
+// A color! This'll be some CSS-ready value.
+
+import {isColor} from '#validators';
+
+// TODO: Not templateCompositeFrom.
+
+export default function() {
+  return {
+    flags: {update: true, expose: true},
+    update: {validate: isColor},
+  };
+}
diff --git a/src/data/composite/wiki-properties/commentary.js b/src/data/composite/wiki-properties/commentary.js
new file mode 100644
index 00000000..fbea9d5c
--- /dev/null
+++ b/src/data/composite/wiki-properties/commentary.js
@@ -0,0 +1,12 @@
+// Artist commentary! Generally present on tracks and albums.
+
+import {isCommentary} from '#validators';
+
+// TODO: Not templateCompositeFrom.
+
+export default function() {
+  return {
+    flags: {update: true, expose: true},
+    update: {validate: isCommentary},
+  };
+}
diff --git a/src/data/composite/wiki-properties/commentatorArtists.js b/src/data/composite/wiki-properties/commentatorArtists.js
new file mode 100644
index 00000000..52aeb868
--- /dev/null
+++ b/src/data/composite/wiki-properties/commentatorArtists.js
@@ -0,0 +1,55 @@
+// This one's kinda tricky: it parses artist "references" from the
+// commentary content, and finds the matching artist for each reference.
+// This is mostly useful for credits and listings on artist pages.
+
+import {input, templateCompositeFrom} from '#composite';
+import find from '#find';
+import {unique} from '#sugar';
+
+import {exitWithoutDependency} from '#composite/control-flow';
+import {withResolvedReferenceList} from '#composite/wiki-data';
+
+export default templateCompositeFrom({
+  annotation: `commentatorArtists`,
+
+  compose: false,
+
+  steps: () => [
+    exitWithoutDependency({
+      dependency: 'commentary',
+      mode: input.value('falsy'),
+      value: input.value([]),
+    }),
+
+    {
+      dependencies: ['commentary'],
+      compute: (continuation, {commentary}) =>
+        continuation({
+          '#artistRefs':
+            Array.from(
+              commentary
+                .replace(/<\/?b>/g, '')
+                .matchAll(/<i>(?<who>.*?):<\/i>/g))
+              .map(({groups: {who}}) => who),
+        }),
+    },
+
+    withResolvedReferenceList({
+      list: '#artistRefs',
+      data: 'artistData',
+      find: input.value(find.artist),
+    }).outputs({
+      '#resolvedReferenceList': '#artists',
+    }),
+
+    {
+      flags: {expose: true},
+
+      expose: {
+        dependencies: ['#artists'],
+        compute: ({'#artists': artists}) =>
+          unique(artists),
+      },
+    },
+  ],
+});
diff --git a/src/data/composite/wiki-properties/contribsPresent.js b/src/data/composite/wiki-properties/contribsPresent.js
new file mode 100644
index 00000000..24f302a5
--- /dev/null
+++ b/src/data/composite/wiki-properties/contribsPresent.js
@@ -0,0 +1,30 @@
+// Nice 'n simple shorthand for an exposed-only flag which is true when any
+// contributions are present in the specified property.
+
+import {input, templateCompositeFrom} from '#composite';
+import {isContributionList} from '#validators';
+
+import {exposeDependency, withResultOfAvailabilityCheck}
+  from '#composite/control-flow';
+
+export default templateCompositeFrom({
+  annotation: `contribsPresent`,
+
+  compose: false,
+
+  inputs: {
+    contribs: input.staticDependency({
+      validate: isContributionList,
+      acceptsNull: true,
+    }),
+  },
+
+  steps: () => [
+    withResultOfAvailabilityCheck({
+      from: input('contribs'),
+      mode: input.value('empty'),
+    }),
+
+    exposeDependency({dependency: '#availability'}),
+  ],
+});
diff --git a/src/data/composite/wiki-properties/contributionList.js b/src/data/composite/wiki-properties/contributionList.js
new file mode 100644
index 00000000..8fde2caa
--- /dev/null
+++ b/src/data/composite/wiki-properties/contributionList.js
@@ -0,0 +1,35 @@
+// Strong 'n sturdy contribution list, rolling a list of references (provided
+// as this property's update value) and the resolved results (as get exposed)
+// into one property. Update value will look something like this:
+//
+//   [
+//     {who: 'Artist Name', what: 'Viola'},
+//     {who: 'artist:john-cena', what: null},
+//     ...
+//   ]
+//
+// ...typically as processed from YAML, spreadsheet, or elsewhere.
+// Exposes as the same, but with the "who" replaced with matches found in
+// artistData - which means this always depends on an `artistData` property
+// also existing on this object!
+//
+
+import {input, templateCompositeFrom} from '#composite';
+import {isContributionList} from '#validators';
+
+import {exposeConstant, exposeDependencyOrContinue} from '#composite/control-flow';
+import {withResolvedContribs} from '#composite/wiki-data';
+
+export default templateCompositeFrom({
+  annotation: `contributionList`,
+
+  compose: false,
+
+  update: {validate: isContributionList},
+
+  steps: () => [
+    withResolvedContribs({from: input.updateValue()}),
+    exposeDependencyOrContinue({dependency: '#resolvedContribs'}),
+    exposeConstant({value: input.value([])}),
+  ],
+});
diff --git a/src/data/composite/wiki-properties/dimensions.js b/src/data/composite/wiki-properties/dimensions.js
new file mode 100644
index 00000000..57a01279
--- /dev/null
+++ b/src/data/composite/wiki-properties/dimensions.js
@@ -0,0 +1,13 @@
+// Plain ol' image dimensions. This is a two-item array of positive integers,
+// corresponding to width and height respectively.
+
+import {isDimensions} from '#validators';
+
+// TODO: Not templateCompositeFrom.
+
+export default function() {
+  return {
+    flags: {update: true, expose: true},
+    update: {validate: isDimensions},
+  };
+}
diff --git a/src/data/composite/wiki-properties/directory.js b/src/data/composite/wiki-properties/directory.js
new file mode 100644
index 00000000..0b2181c9
--- /dev/null
+++ b/src/data/composite/wiki-properties/directory.js
@@ -0,0 +1,23 @@
+// The all-encompassing "directory" property, used as the unique identifier for
+// almost any data object. Also corresponds to a part of the URL which pages of
+// such objects are visited at.
+
+import {isDirectory} from '#validators';
+import {getKebabCase} from '#wiki-data';
+
+// TODO: Not templateCompositeFrom.
+
+export default function() {
+  return {
+    flags: {update: true, expose: true},
+    update: {validate: isDirectory},
+    expose: {
+      dependencies: ['name'],
+      transform(directory, {name}) {
+        if (directory === null && name === null) return null;
+        else if (directory === null) return getKebabCase(name);
+        else return directory;
+      },
+    },
+  };
+}
diff --git a/src/data/composite/wiki-properties/duration.js b/src/data/composite/wiki-properties/duration.js
new file mode 100644
index 00000000..827f282d
--- /dev/null
+++ b/src/data/composite/wiki-properties/duration.js
@@ -0,0 +1,13 @@
+// Duration! This is a number of seconds, possibly floating point, always
+// at minimum zero.
+
+import {isDuration} from '#validators';
+
+// TODO: Not templateCompositeFrom.
+
+export default function() {
+  return {
+    flags: {update: true, expose: true},
+    update: {validate: isDuration},
+  };
+}
diff --git a/src/data/composite/wiki-properties/externalFunction.js b/src/data/composite/wiki-properties/externalFunction.js
new file mode 100644
index 00000000..c388da6c
--- /dev/null
+++ b/src/data/composite/wiki-properties/externalFunction.js
@@ -0,0 +1,11 @@
+// External function. These should only be used as dependencies for other
+// properties, so they're left unexposed.
+
+// TODO: Not templateCompositeFrom.
+
+export default function() {
+  return {
+    flags: {update: true},
+    update: {validate: (t) => typeof t === 'function'},
+  };
+}
diff --git a/src/data/composite/wiki-properties/fileExtension.js b/src/data/composite/wiki-properties/fileExtension.js
new file mode 100644
index 00000000..c926fa8b
--- /dev/null
+++ b/src/data/composite/wiki-properties/fileExtension.js
@@ -0,0 +1,13 @@
+// A file extension! Or the default, if provided when calling this.
+
+import {isFileExtension} from '#validators';
+
+// TODO: Not templateCompositeFrom.
+
+export default function(defaultFileExtension = null) {
+  return {
+    flags: {update: true, expose: true},
+    update: {validate: isFileExtension},
+    expose: {transform: (value) => value ?? defaultFileExtension},
+  };
+}
diff --git a/src/data/composite/wiki-properties/flag.js b/src/data/composite/wiki-properties/flag.js
new file mode 100644
index 00000000..076e663f
--- /dev/null
+++ b/src/data/composite/wiki-properties/flag.js
@@ -0,0 +1,19 @@
+// Straightforward flag descriptor for a variety of property purposes.
+// Provide a default value, true or false!
+
+import {isBoolean} from '#validators';
+
+// TODO: Not templateCompositeFrom.
+
+// TODO: The description is a lie. This defaults to false. Bad.
+
+export default function(defaultValue = false) {
+  if (typeof defaultValue !== 'boolean') {
+    throw new TypeError(`Always set explicit defaults for flags!`);
+  }
+
+  return {
+    flags: {update: true, expose: true},
+    update: {validate: isBoolean, default: defaultValue},
+  };
+}
diff --git a/src/data/composite/wiki-properties/index.js b/src/data/composite/wiki-properties/index.js
new file mode 100644
index 00000000..2462b047
--- /dev/null
+++ b/src/data/composite/wiki-properties/index.js
@@ -0,0 +1,20 @@
+export {default as additionalFiles} from './additionalFiles.js';
+export {default as color} from './color.js';
+export {default as commentary} from './commentary.js';
+export {default as commentatorArtists} from './commentatorArtists.js';
+export {default as contribsPresent} from './contribsPresent.js';
+export {default as contributionList} from './contributionList.js';
+export {default as dimensions} from './dimensions.js';
+export {default as directory} from './directory.js';
+export {default as duration} from './duration.js';
+export {default as externalFunction} from './externalFunction.js';
+export {default as fileExtension} from './fileExtension.js';
+export {default as flag} from './flag.js';
+export {default as name} from './name.js';
+export {default as referenceList} from './referenceList.js';
+export {default as reverseReferenceList} from './reverseReferenceList.js';
+export {default as simpleDate} from './simpleDate.js';
+export {default as simpleString} from './simpleString.js';
+export {default as singleReference} from './singleReference.js';
+export {default as urls} from './urls.js';
+export {default as wikiData} from './wikiData.js';
diff --git a/src/data/composite/wiki-properties/name.js b/src/data/composite/wiki-properties/name.js
new file mode 100644
index 00000000..5146488b
--- /dev/null
+++ b/src/data/composite/wiki-properties/name.js
@@ -0,0 +1,11 @@
+// A wiki data object's name! Its directory (i.e. unique identifier) will be
+// computed based on this value if not otherwise specified.
+
+import {isName} from '#validators';
+
+export default function(defaultName) {
+  return {
+    flags: {update: true, expose: true},
+    update: {validate: isName, default: defaultName},
+  };
+}
diff --git a/src/data/composite/wiki-properties/referenceList.js b/src/data/composite/wiki-properties/referenceList.js
new file mode 100644
index 00000000..f5b6c58e
--- /dev/null
+++ b/src/data/composite/wiki-properties/referenceList.js
@@ -0,0 +1,47 @@
+// Stores and exposes a list of references to other data objects; all items
+// must be references to the same type, which is specified on the class input.
+//
+// See also:
+//  - singleReference
+//  - withResolvedReferenceList
+//
+
+import {input, templateCompositeFrom} from '#composite';
+import {validateReferenceList} from '#validators';
+
+import {exposeDependency} from '#composite/control-flow';
+import {inputThingClass, inputWikiData, withResolvedReferenceList}
+  from '#composite/wiki-data';
+
+// TODO: Kludge.
+import Thing from '../../things/thing.js';
+
+export default templateCompositeFrom({
+  annotation: `referenceList`,
+
+  compose: false,
+
+  inputs: {
+    class: inputThingClass(),
+
+    data: inputWikiData({allowMixedTypes: false}),
+    find: input({type: 'function'}),
+  },
+
+  update: ({
+    [input.staticValue('class')]: thingClass,
+  }) => {
+    const {[Thing.referenceType]: referenceType} = thingClass;
+    return {validate: validateReferenceList(referenceType)};
+  },
+
+  steps: () => [
+    withResolvedReferenceList({
+      list: input.updateValue(),
+      data: input('data'),
+      find: input('find'),
+    }),
+
+    exposeDependency({dependency: '#resolvedReferenceList'}),
+  ],
+});
diff --git a/src/data/composite/wiki-properties/reverseReferenceList.js b/src/data/composite/wiki-properties/reverseReferenceList.js
new file mode 100644
index 00000000..84ba67df
--- /dev/null
+++ b/src/data/composite/wiki-properties/reverseReferenceList.js
@@ -0,0 +1,30 @@
+// Neat little shortcut for "reversing" the reference lists stored on other
+// things - for example, tracks specify a "referenced tracks" property, and
+// you would use this to compute a corresponding "referenced *by* tracks"
+// property. Naturally, the passed ref list property is of the things in the
+// wiki data provided, not the requesting Thing itself.
+
+import {input, templateCompositeFrom} from '#composite';
+
+import {exposeDependency} from '#composite/control-flow';
+import {inputWikiData, withReverseReferenceList} from '#composite/wiki-data';
+
+export default templateCompositeFrom({
+  annotation: `reverseReferenceList`,
+
+  compose: false,
+
+  inputs: {
+    data: inputWikiData({allowMixedTypes: false}),
+    list: input({type: 'string'}),
+  },
+
+  steps: () => [
+    withReverseReferenceList({
+      data: input('data'),
+      list: input('list'),
+    }),
+
+    exposeDependency({dependency: '#reverseReferenceList'}),
+  ],
+});
diff --git a/src/data/composite/wiki-properties/simpleDate.js b/src/data/composite/wiki-properties/simpleDate.js
new file mode 100644
index 00000000..f08d8323
--- /dev/null
+++ b/src/data/composite/wiki-properties/simpleDate.js
@@ -0,0 +1,14 @@
+// General date type, used as the descriptor for a bunch of properties.
+// This isn't dynamic though - it won't inherit from a date stored on
+// another object, for example.
+
+import {isDate} from '#validators';
+
+// TODO: Not templateCompositeFrom.
+
+export default function() {
+  return {
+    flags: {update: true, expose: true},
+    update: {validate: isDate},
+  };
+}
diff --git a/src/data/composite/wiki-properties/simpleString.js b/src/data/composite/wiki-properties/simpleString.js
new file mode 100644
index 00000000..18d65146
--- /dev/null
+++ b/src/data/composite/wiki-properties/simpleString.js
@@ -0,0 +1,14 @@
+// General string type. This should probably generally be avoided in favor
+// of more specific validation, but using it makes it easy to find where we
+// might want to improve later, and it's a useful shorthand meanwhile.
+
+import {isString} from '#validators';
+
+// TODO: Not templateCompositeFrom.
+
+export default function() {
+  return {
+    flags: {update: true, expose: true},
+    update: {validate: isString},
+  };
+}
diff --git a/src/data/composite/wiki-properties/singleReference.js b/src/data/composite/wiki-properties/singleReference.js
new file mode 100644
index 00000000..34bd2e6d
--- /dev/null
+++ b/src/data/composite/wiki-properties/singleReference.js
@@ -0,0 +1,47 @@
+// Stores and exposes one connection, or reference, to another data object.
+// The reference must be to a specific type, which is specified on the class
+// input.
+//
+// See also:
+//  - referenceList
+//  - withResolvedReference
+//
+
+import {input, templateCompositeFrom} from '#composite';
+import {validateReference} from '#validators';
+
+import {exposeDependency} from '#composite/control-flow';
+import {inputThingClass, inputWikiData, withResolvedReference}
+  from '#composite/wiki-data';
+
+// TODO: Kludge.
+import Thing from '../../things/thing.js';
+
+export default templateCompositeFrom({
+  annotation: `singleReference`,
+
+  compose: false,
+
+  inputs: {
+    class: inputThingClass(),
+    find: input({type: 'function'}),
+    data: inputWikiData({allowMixedTypes: false}),
+  },
+
+  update: ({
+    [input.staticValue('class')]: thingClass,
+  }) => {
+    const {[Thing.referenceType]: referenceType} = thingClass;
+    return {validate: validateReference(referenceType)};
+  },
+
+  steps: () => [
+    withResolvedReference({
+      ref: input.updateValue(),
+      data: input('data'),
+      find: input('find'),
+    }),
+
+    exposeDependency({dependency: '#resolvedReference'}),
+  ],
+});
diff --git a/src/data/composite/wiki-properties/urls.js b/src/data/composite/wiki-properties/urls.js
new file mode 100644
index 00000000..3160a0bf
--- /dev/null
+++ b/src/data/composite/wiki-properties/urls.js
@@ -0,0 +1,14 @@
+// A list of URLs! This will always be present on the data object, even if set
+// to an empty array or null.
+
+import {isURL, validateArrayItems} from '#validators';
+
+// TODO: Not templateCompositeFrom.
+
+export default function() {
+  return {
+    flags: {update: true, expose: true},
+    update: {validate: validateArrayItems(isURL)},
+    expose: {transform: value => value ?? []},
+  };
+}
diff --git a/src/data/composite/wiki-properties/wikiData.js b/src/data/composite/wiki-properties/wikiData.js
new file mode 100644
index 00000000..4ea47785
--- /dev/null
+++ b/src/data/composite/wiki-properties/wikiData.js
@@ -0,0 +1,17 @@
+// General purpose wiki data constructor, for properties like artistData,
+// trackData, etc.
+
+import {validateArrayItems, validateInstanceOf} from '#validators';
+
+// TODO: Not templateCompositeFrom.
+
+// TODO: This should validate with validateWikiData.
+
+export default function(thingClass) {
+  return {
+    flags: {update: true},
+    update: {
+      validate: validateArrayItems(validateInstanceOf(thingClass)),
+    },
+  };
+}
diff --git a/src/data/things/album.js b/src/data/things/album.js
index c012c243..546fda3b 100644
--- a/src/data/things/album.js
+++ b/src/data/things/album.js
@@ -1,163 +1,143 @@
-import {empty} from '#sugar';
+import {input} from '#composite';
 import find from '#find';
+import {isDate} from '#validators';
+
+import {exposeDependency, exposeUpdateValueOrContinue}
+  from '#composite/control-flow';
+import {exitWithoutContribs} from '#composite/wiki-data';
+
+import {
+  additionalFiles,
+  commentary,
+  color,
+  commentatorArtists,
+  contribsPresent,
+  contributionList,
+  dimensions,
+  directory,
+  fileExtension,
+  flag,
+  name,
+  referenceList,
+  simpleDate,
+  simpleString,
+  urls,
+  wikiData,
+} from '#composite/wiki-properties';
+
+import {
+  withTracks,
+  withTrackSections,
+} from '#composite/things/album';
 
 import Thing from './thing.js';
 
 export class Album extends Thing {
   static [Thing.referenceType] = 'album';
 
-  static [Thing.getPropertyDescriptors] = ({
-    ArtTag,
-    Artist,
-    Group,
-    Track,
-
-    validators: {
-      isDate,
-      isDimensions,
-      isTrackSectionList,
-    },
-  }) => ({
+  static [Thing.getPropertyDescriptors] = ({ArtTag, Artist, Group, Track}) => ({
     // Update & expose
 
-    name: Thing.common.name('Unnamed Album'),
-    color: Thing.common.color(),
-    directory: Thing.common.directory(),
-    urls: Thing.common.urls(),
-
-    date: Thing.common.simpleDate(),
-    trackArtDate: Thing.common.simpleDate(),
-    dateAddedToWiki: Thing.common.simpleDate(),
-
-    coverArtDate: {
-      flags: {update: true, expose: true},
-
-      update: {validate: isDate},
-
-      expose: {
-        dependencies: ['date', 'coverArtistContribsByRef'],
-        transform: (coverArtDate, {
-          coverArtistContribsByRef,
-          date,
-        }) =>
-          (!empty(coverArtistContribsByRef)
-            ? coverArtDate ?? date ?? null
-            : null),
-      },
-    },
-
-    artistContribsByRef: Thing.common.contribsByRef(),
-    coverArtistContribsByRef: Thing.common.contribsByRef(),
-    trackCoverArtistContribsByRef: Thing.common.contribsByRef(),
-    wallpaperArtistContribsByRef: Thing.common.contribsByRef(),
-    bannerArtistContribsByRef: Thing.common.contribsByRef(),
-
-    groupsByRef: Thing.common.referenceList(Group),
-    artTagsByRef: Thing.common.referenceList(ArtTag),
-
-    trackSections: {
-      flags: {update: true, expose: true},
-
-      update: {
-        validate: isTrackSectionList,
-      },
-
-      expose: {
-        dependencies: ['color', 'trackData'],
-        transform(trackSections, {
-          color: albumColor,
-          trackData,
-        }) {
-          let startIndex = 0;
-          return trackSections?.map(section => ({
-            name: section.name ?? null,
-            color: section.color ?? albumColor ?? null,
-            dateOriginallyReleased: section.dateOriginallyReleased ?? null,
-            isDefaultTrackSection: section.isDefaultTrackSection ?? false,
-
-            startIndex: (
-              startIndex += section.tracksByRef.length,
-              startIndex - section.tracksByRef.length
-            ),
-
-            tracksByRef: section.tracksByRef ?? [],
-            tracks:
-              (trackData && section.tracksByRef
-                ?.map(ref => find.track(ref, trackData, {mode: 'quiet'}))
-                .filter(Boolean)) ??
-              [],
-          }));
-        },
-      },
-    },
-
-    coverArtFileExtension: Thing.common.fileExtension('jpg'),
-    trackCoverArtFileExtension: Thing.common.fileExtension('jpg'),
-
-    wallpaperStyle: Thing.common.simpleString(),
-    wallpaperFileExtension: Thing.common.fileExtension('jpg'),
-
-    bannerStyle: Thing.common.simpleString(),
-    bannerFileExtension: Thing.common.fileExtension('jpg'),
-    bannerDimensions: {
-      flags: {update: true, expose: true},
-      update: {validate: isDimensions},
-    },
-
-    hasTrackNumbers: Thing.common.flag(true),
-    isListedOnHomepage: Thing.common.flag(true),
-    isListedInGalleries: Thing.common.flag(true),
-
-    commentary: Thing.common.commentary(),
-    additionalFiles: Thing.common.additionalFiles(),
+    name: name('Unnamed Album'),
+    color: color(),
+    directory: directory(),
+    urls: urls(),
+
+    date: simpleDate(),
+    trackArtDate: simpleDate(),
+    dateAddedToWiki: simpleDate(),
+
+    coverArtDate: [
+      exitWithoutContribs({contribs: 'coverArtistContribs'}),
+
+      exposeUpdateValueOrContinue({
+        validate: input.value(isDate),
+      }),
+
+      exposeDependency({dependency: 'date'}),
+    ],
+
+    coverArtFileExtension: [
+      exitWithoutContribs({contribs: 'coverArtistContribs'}),
+      fileExtension('jpg'),
+    ],
+
+    trackCoverArtFileExtension: fileExtension('jpg'),
+
+    wallpaperFileExtension: [
+      exitWithoutContribs({contribs: 'wallpaperArtistContribs'}),
+      fileExtension('jpg'),
+    ],
+
+    bannerFileExtension: [
+      exitWithoutContribs({contribs: 'bannerArtistContribs'}),
+      fileExtension('jpg'),
+    ],
+
+    wallpaperStyle: [
+      exitWithoutContribs({contribs: 'wallpaperArtistContribs'}),
+      simpleString(),
+    ],
+
+    bannerStyle: [
+      exitWithoutContribs({contribs: 'bannerArtistContribs'}),
+      simpleString(),
+    ],
+
+    bannerDimensions: [
+      exitWithoutContribs({contribs: 'bannerArtistContribs'}),
+      dimensions(),
+    ],
+
+    hasTrackNumbers: flag(true),
+    isListedOnHomepage: flag(true),
+    isListedInGalleries: flag(true),
+
+    commentary: commentary(),
+    additionalFiles: additionalFiles(),
+
+    trackSections: [
+      withTrackSections(),
+      exposeDependency({dependency: '#trackSections'}),
+    ],
+
+    artistContribs: contributionList(),
+    coverArtistContribs: contributionList(),
+    trackCoverArtistContribs: contributionList(),
+    wallpaperArtistContribs: contributionList(),
+    bannerArtistContribs: contributionList(),
+
+    groups: referenceList({
+      class: input.value(Group),
+      find: input.value(find.group),
+      data: 'groupData',
+    }),
+
+    artTags: referenceList({
+      class: input.value(ArtTag),
+      find: input.value(find.artTag),
+      data: 'artTagData',
+    }),
 
     // Update only
 
-    artistData: Thing.common.wikiData(Artist),
-    artTagData: Thing.common.wikiData(ArtTag),
-    groupData: Thing.common.wikiData(Group),
-    trackData: Thing.common.wikiData(Track),
+    artistData: wikiData(Artist),
+    artTagData: wikiData(ArtTag),
+    groupData: wikiData(Group),
+    trackData: wikiData(Track),
 
     // Expose only
 
-    artistContribs: Thing.common.dynamicContribs('artistContribsByRef'),
-    coverArtistContribs: Thing.common.dynamicContribs('coverArtistContribsByRef'),
-    trackCoverArtistContribs: Thing.common.dynamicContribs('trackCoverArtistContribsByRef'),
-    wallpaperArtistContribs: Thing.common.dynamicContribs('wallpaperArtistContribsByRef'),
-    bannerArtistContribs: Thing.common.dynamicContribs('bannerArtistContribsByRef'),
-
-    commentatorArtists: Thing.common.commentatorArtists(),
-
-    hasCoverArt: Thing.common.contribsPresent('coverArtistContribsByRef'),
-    hasWallpaperArt: Thing.common.contribsPresent('wallpaperArtistContribsByRef'),
-    hasBannerArt: Thing.common.contribsPresent('bannerArtistContribsByRef'),
-
-    tracks: {
-      flags: {expose: true},
-
-      expose: {
-        dependencies: ['trackSections', 'trackData'],
-        compute: ({trackSections, trackData}) =>
-          trackSections && trackData
-            ? trackSections
-                .flatMap((section) => section.tracksByRef ?? [])
-                .map((ref) => find.track(ref, trackData, {mode: 'quiet'}))
-                .filter(Boolean)
-            : [],
-      },
-    },
-
-    groups: Thing.common.dynamicThingsFromReferenceList(
-      'groupsByRef',
-      'groupData',
-      find.group
-    ),
-
-    artTags: Thing.common.dynamicThingsFromReferenceList(
-      'artTagsByRef',
-      'artTagData',
-      find.artTag
-    ),
+    commentatorArtists: commentatorArtists(),
+
+    hasCoverArt: contribsPresent({contribs: 'coverArtistContribs'}),
+    hasWallpaperArt: contribsPresent({contribs: 'wallpaperArtistContribs'}),
+    hasBannerArt: contribsPresent({contribs: 'bannerArtistContribs'}),
+
+    tracks: [
+      withTracks(),
+      exposeDependency({dependency: '#tracks'}),
+    ],
   });
 
   static [Thing.getSerializeDescriptors] = ({
@@ -201,10 +181,12 @@ export class Album extends Thing {
 }
 
 export class TrackSectionHelper extends Thing {
+  static [Thing.friendlyName] = `Track Section`;
+
   static [Thing.getPropertyDescriptors] = () => ({
-    name: Thing.common.name('Unnamed Track Group'),
-    color: Thing.common.color(),
-    dateOriginallyReleased: Thing.common.simpleDate(),
-    isDefaultTrackGroup: Thing.common.flag(false),
+    name: name('Unnamed Track Section'),
+    color: color(),
+    dateOriginallyReleased: simpleDate(),
+    isDefaultTrackGroup: flag(false),
   })
 }
diff --git a/src/data/things/art-tag.js b/src/data/things/art-tag.js
index c103c4d5..6503beec 100644
--- a/src/data/things/art-tag.js
+++ b/src/data/things/art-tag.js
@@ -1,35 +1,47 @@
+import {input} from '#composite';
 import {sortAlbumsTracksChronologically} from '#wiki-data';
+import {isName} from '#validators';
+
+import {exposeUpdateValueOrContinue} from '#composite/control-flow';
+
+import {
+  color,
+  directory,
+  flag,
+  name,
+  wikiData,
+} from '#composite/wiki-properties';
 
 import Thing from './thing.js';
 
 export class ArtTag extends Thing {
   static [Thing.referenceType] = 'tag';
+  static [Thing.friendlyName] = `Art Tag`;
 
-  static [Thing.getPropertyDescriptors] = ({
-    Album,
-    Track,
-  }) => ({
+  static [Thing.getPropertyDescriptors] = ({Album, Track}) => ({
     // Update & expose
 
-    name: Thing.common.name('Unnamed Art Tag'),
-    directory: Thing.common.directory(),
-    color: Thing.common.color(),
-    isContentWarning: Thing.common.flag(false),
+    name: name('Unnamed Art Tag'),
+    directory: directory(),
+    color: color(),
+    isContentWarning: flag(false),
 
-    nameShort: {
-      flags: {update: true, expose: true},
+    nameShort: [
+      exposeUpdateValueOrContinue({
+        validate: input.value(isName),
+      }),
 
-      expose: {
+      {
         dependencies: ['name'],
-        transform: (value, {name}) =>
-          value ?? name.replace(/ \(.*?\)$/, ''),
+        compute: ({name}) =>
+          name.replace(/ \([^)]*?\)$/, ''),
       },
-    },
+    ],
 
     // Update only
 
-    albumData: Thing.common.wikiData(Album),
-    trackData: Thing.common.wikiData(Track),
+    albumData: wikiData(Album),
+    trackData: wikiData(Track),
 
     // Expose only
 
@@ -37,8 +49,8 @@ export class ArtTag extends Thing {
       flags: {expose: true},
 
       expose: {
-        dependencies: ['albumData', 'trackData'],
-        compute: ({albumData, trackData, [ArtTag.instance]: artTag}) =>
+        dependencies: ['this', 'albumData', 'trackData'],
+        compute: ({this: artTag, albumData, trackData}) =>
           sortAlbumsTracksChronologically(
             [...albumData, ...trackData]
               .filter(({artTags}) => artTags.includes(artTag)),
diff --git a/src/data/things/artist.js b/src/data/things/artist.js
index 6d4f4a0d..1b313db6 100644
--- a/src/data/things/artist.js
+++ b/src/data/things/artist.js
@@ -1,29 +1,33 @@
+import {input} from '#composite';
 import find from '#find';
+import {isName, validateArrayItems} from '#validators';
+
+import {
+  directory,
+  fileExtension,
+  flag,
+  name,
+  simpleString,
+  singleReference,
+  urls,
+  wikiData,
+} from '#composite/wiki-properties';
 
 import Thing from './thing.js';
 
 export class Artist extends Thing {
   static [Thing.referenceType] = 'artist';
 
-  static [Thing.getPropertyDescriptors] = ({
-    Album,
-    Flash,
-    Track,
-
-    validators: {
-      isName,
-      validateArrayItems,
-    },
-  }) => ({
+  static [Thing.getPropertyDescriptors] = ({Album, Flash, Track}) => ({
     // Update & expose
 
-    name: Thing.common.name('Unnamed Artist'),
-    directory: Thing.common.directory(),
-    urls: Thing.common.urls(),
-    contextNotes: Thing.common.simpleString(),
+    name: name('Unnamed Artist'),
+    directory: directory(),
+    urls: urls(),
+    contextNotes: simpleString(),
 
-    hasAvatar: Thing.common.flag(false),
-    avatarFileExtension: Thing.common.fileExtension('jpg'),
+    hasAvatar: flag(false),
+    avatarFileExtension: fileExtension('jpg'),
 
     aliasNames: {
       flags: {update: true, expose: true},
@@ -31,30 +35,23 @@ export class Artist extends Thing {
       expose: {transform: (names) => names ?? []},
     },
 
-    isAlias: Thing.common.flag(),
-    aliasedArtistRef: Thing.common.singleReference(Artist),
+    isAlias: flag(),
+
+    aliasedArtist: singleReference({
+      class: input.value(Artist),
+      find: input.value(find.artist),
+      data: 'artistData',
+    }),
 
     // Update only
 
-    albumData: Thing.common.wikiData(Album),
-    artistData: Thing.common.wikiData(Artist),
-    flashData: Thing.common.wikiData(Flash),
-    trackData: Thing.common.wikiData(Track),
+    albumData: wikiData(Album),
+    artistData: wikiData(Artist),
+    flashData: wikiData(Flash),
+    trackData: wikiData(Track),
 
     // Expose only
 
-    aliasedArtist: {
-      flags: {expose: true},
-
-      expose: {
-        dependencies: ['artistData', 'aliasedArtistRef'],
-        compute: ({artistData, aliasedArtistRef}) =>
-          aliasedArtistRef && artistData
-            ? find.artist(aliasedArtistRef, artistData, {mode: 'quiet'})
-            : null,
-      },
-    },
-
     tracksAsArtist:
       Artist.filterByContrib('trackData', 'artistContribs'),
     tracksAsContributor:
@@ -66,14 +63,14 @@ export class Artist extends Thing {
       flags: {expose: true},
 
       expose: {
-        dependencies: ['trackData'],
+        dependencies: ['this', 'trackData'],
 
-        compute: ({trackData, [Artist.instance]: artist}) =>
+        compute: ({this: artist, trackData}) =>
           trackData?.filter((track) =>
             [
-              ...track.artistContribs,
-              ...track.contributorContribs,
-              ...track.coverArtistContribs,
+              ...track.artistContribs ?? [],
+              ...track.contributorContribs ?? [],
+              ...track.coverArtistContribs ?? [],
             ].some(({who}) => who === artist)) ?? [],
       },
     },
@@ -82,9 +79,9 @@ export class Artist extends Thing {
       flags: {expose: true},
 
       expose: {
-        dependencies: ['trackData'],
+        dependencies: ['this', 'trackData'],
 
-        compute: ({trackData, [Artist.instance]: artist}) =>
+        compute: ({this: artist, trackData}) =>
           trackData?.filter(({commentatorArtists}) =>
             commentatorArtists.includes(artist)) ?? [],
       },
@@ -120,18 +117,16 @@ export class Artist extends Thing {
       flags: {expose: true},
 
       expose: {
-        dependencies: ['albumData'],
+        dependencies: ['this', 'albumData'],
 
-        compute: ({albumData, [Artist.instance]: artist}) =>
+        compute: ({this: artist, albumData}) =>
           albumData?.filter(({commentatorArtists}) =>
             commentatorArtists.includes(artist)) ?? [],
       },
     },
 
-    flashesAsContributor: Artist.filterByContrib(
-      'flashData',
-      'contributorContribs'
-    ),
+    flashesAsContributor:
+      Artist.filterByContrib('flashData', 'contributorContribs'),
   });
 
   static [Thing.getSerializeDescriptors] = ({
@@ -165,15 +160,15 @@ export class Artist extends Thing {
     flags: {expose: true},
 
     expose: {
-      dependencies: [thingDataProperty],
+      dependencies: ['this', thingDataProperty],
 
       compute: ({
+        this: artist,
         [thingDataProperty]: thingData,
-        [Artist.instance]: artist
       }) =>
         thingData?.filter(thing =>
           thing[contribsProperty]
-            .some(contrib => contrib.who === artist)) ?? [],
+            ?.some(contrib => contrib.who === artist)) ?? [],
     },
   });
 }
diff --git a/src/data/things/cacheable-object.js b/src/data/things/cacheable-object.js
index ea705a61..9fda865e 100644
--- a/src/data/things/cacheable-object.js
+++ b/src/data/things/cacheable-object.js
@@ -76,28 +76,24 @@
 
 import {inspect as nodeInspect} from 'node:util';
 
-import {color, ENABLE_COLOR} from '#cli';
+import {colors, ENABLE_COLOR} from '#cli';
 
 function inspect(value) {
   return nodeInspect(value, {colors: ENABLE_COLOR});
 }
 
 export default class CacheableObject {
-  static instance = Symbol('CacheableObject `this` instance');
-
   #propertyUpdateValues = Object.create(null);
   #propertyUpdateCacheInvalidators = Object.create(null);
 
-  /*
-    // Note the constructor doesn't take an initial data source. Due to a quirk
-    // of JavaScript, private members can't be accessed before the superclass's
-    // constructor is finished processing - so if we call the overridden
-    // update() function from inside this constructor, it will error when
-    // writing to private members. Pretty bad!
-    //
-    // That means initial data must be provided by following up with update()
-    // after constructing the new instance of the Thing (sub)class.
-    */
+  // Note the constructor doesn't take an initial data source. Due to a quirk
+  // of JavaScript, private members can't be accessed before the superclass's
+  // constructor is finished processing - so if we call the overridden
+  // update() function from inside this constructor, it will error when
+  // writing to private members. Pretty bad!
+  //
+  // That means initial data must be provided by following up with update()
+  // after constructing the new instance of the Thing (sub)class.
 
   constructor() {
     this.#defineProperties();
@@ -143,7 +139,7 @@ export default class CacheableObject {
 
       const definition = {
         configurable: false,
-        enumerable: true,
+        enumerable: flags.expose,
       };
 
       if (flags.update) {
@@ -183,13 +179,8 @@ export default class CacheableObject {
           } else if (result !== true) {
             throw new TypeError(`Validation failed for value ${newValue}`);
           }
-        } catch (error) {
-          error.message = [
-            `Property ${color.green(property)}`,
-            `(${inspect(this[property])} -> ${inspect(newValue)}):`,
-            error.message
-          ].join(' ');
-          throw error;
+        } catch (caughtError) {
+          throw new CacheableObjectPropertyValueError(property, this[property], newValue, caughtError);
         }
       }
 
@@ -250,20 +241,27 @@ export default class CacheableObject {
 
     let getAllDependencies;
 
-    const dependencyKeys = expose.dependencies;
-    if (dependencyKeys?.length > 0) {
-      const reflectionEntry = [this.constructor.instance, this];
-      const dependencyGetters = dependencyKeys
-        .map(key => () => [key, this.#propertyUpdateValues[key]]);
+    if (expose.dependencies?.length > 0) {
+      const dependencyKeys = expose.dependencies.slice();
+      const shouldReflect = dependencyKeys.includes('this');
+
+      getAllDependencies = () => {
+        const dependencies = Object.create(null);
+
+        for (const key of dependencyKeys) {
+          dependencies[key] = this.#propertyUpdateValues[key];
+        }
+
+        if (shouldReflect) {
+          dependencies.this = this;
+        }
 
-      getAllDependencies = () =>
-        Object.fromEntries(dependencyGetters
-          .map(f => f())
-          .concat([reflectionEntry]));
+        return dependencies;
+      };
     } else {
-      const allDependencies = {[this.constructor.instance]: this};
-      Object.freeze(allDependencies);
-      getAllDependencies = () => allDependencies;
+      const dependencies = Object.create(null);
+      Object.freeze(dependencies);
+      getAllDependencies = () => dependencies;
     }
 
     if (flags.update) {
@@ -347,4 +345,22 @@ export default class CacheableObject {
       console.log(` - ${line}`);
     }
   }
+
+  static getUpdateValue(object, key) {
+    if (!Object.hasOwn(object, key)) {
+      return undefined;
+    }
+
+    return object.#propertyUpdateValues[key] ?? null;
+  }
+}
+
+export class CacheableObjectPropertyValueError extends Error {
+  constructor(property, oldValue, newValue, error) {
+    super(
+      `Error setting ${colors.green(property)} (${inspect(oldValue)} -> ${inspect(newValue)})`,
+      {cause: error});
+
+    this.property = property;
+  }
 }
diff --git a/src/data/things/composite.js b/src/data/things/composite.js
new file mode 100644
index 00000000..51525bc1
--- /dev/null
+++ b/src/data/things/composite.js
@@ -0,0 +1,1301 @@
+import {inspect} from 'node:util';
+
+import {colors} from '#cli';
+import {TupleMap} from '#wiki-data';
+import {a} from '#validators';
+
+import {
+  decorateErrorWithIndex,
+  empty,
+  filterProperties,
+  openAggregate,
+  stitchArrays,
+  typeAppearance,
+  unique,
+  withAggregate,
+} from '#sugar';
+
+const globalCompositeCache = {};
+
+const _valueIntoToken = shape =>
+  (value = null) =>
+    (value === null
+      ? Symbol.for(`hsmusic.composite.${shape}`)
+   : typeof value === 'string'
+      ? Symbol.for(`hsmusic.composite.${shape}:${value}`)
+      : {
+          symbol: Symbol.for(`hsmusic.composite.input`),
+          shape,
+          value,
+        });
+
+export const input = _valueIntoToken('input');
+input.symbol = Symbol.for('hsmusic.composite.input');
+
+input.value = _valueIntoToken('input.value');
+input.dependency = _valueIntoToken('input.dependency');
+
+input.myself = () => Symbol.for(`hsmusic.composite.input.myself`);
+
+input.updateValue = _valueIntoToken('input.updateValue');
+
+input.staticDependency = _valueIntoToken('input.staticDependency');
+input.staticValue = _valueIntoToken('input.staticValue');
+
+function isInputToken(token) {
+  if (token === null) {
+    return false;
+  } else if (typeof token === 'object') {
+    return token.symbol === Symbol.for('hsmusic.composite.input');
+  } else if (typeof token === 'symbol') {
+    return token.description.startsWith('hsmusic.composite.input');
+  } else {
+    return false;
+  }
+}
+
+function getInputTokenShape(token) {
+  if (!isInputToken(token)) {
+    throw new TypeError(`Expected an input token, got ${typeAppearance(token)}`);
+  }
+
+  if (typeof token === 'object') {
+    return token.shape;
+  } else {
+    return token.description.match(/hsmusic\.composite\.(input.*?)(:|$)/)[1];
+  }
+}
+
+function getInputTokenValue(token) {
+  if (!isInputToken(token)) {
+    throw new TypeError(`Expected an input token, got ${typeAppearance(token)}`);
+  }
+
+  if (typeof token === 'object') {
+    return token.value;
+  } else {
+    return token.description.match(/hsmusic\.composite\.input.*?:(.*)/)?.[1] ?? null;
+  }
+}
+
+function getStaticInputMetadata(inputOptions) {
+  const metadata = {};
+
+  for (const [name, token] of Object.entries(inputOptions)) {
+    if (typeof token === 'string') {
+      metadata[input.staticDependency(name)] = token;
+      metadata[input.staticValue(name)] = null;
+    } else if (isInputToken(token)) {
+      const tokenShape = getInputTokenShape(token);
+      const tokenValue = getInputTokenValue(token);
+
+      metadata[input.staticDependency(name)] =
+        (tokenShape === 'input.dependency'
+          ? tokenValue
+          : null);
+
+      metadata[input.staticValue(name)] =
+        (tokenShape === 'input.value'
+          ? tokenValue
+          : null);
+    } else {
+      metadata[input.staticDependency(name)] = null;
+      metadata[input.staticValue(name)] = null;
+    }
+  }
+
+  return metadata;
+}
+
+function getCompositionName(description) {
+  return (
+    (description.annotation
+      ? description.annotation
+      : `unnamed composite`));
+}
+
+function validateInputValue(value, description) {
+  const tokenValue = getInputTokenValue(description);
+
+  const {acceptsNull, defaultValue, type, validate} = tokenValue || {};
+
+  if (value === null || value === undefined) {
+    if (acceptsNull || defaultValue === null) {
+      return true;
+    } else {
+      throw new TypeError(
+        (type
+          ? `Expected ${a(type)}, got ${typeAppearance(value)}`
+          : `Expected a value, got ${typeAppearance(value)}`));
+    }
+  }
+
+  if (type) {
+    // Note: null is already handled earlier in this function, so it won't
+    // cause any trouble here.
+    const typeofValue =
+      (typeof value === 'object'
+        ? Array.isArray(value) ? 'array' : 'object'
+        : typeof value);
+
+    if (typeofValue !== type) {
+      throw new TypeError(`Expected ${a(type)}, got ${typeAppearance(value)}`);
+    }
+  }
+
+  if (validate) {
+    validate(value);
+  }
+
+  return true;
+}
+
+export function templateCompositeFrom(description) {
+  const compositionName = getCompositionName(description);
+
+  withAggregate({message: `Errors in description for ${compositionName}`}, ({map, nest, push}) => {
+    if ('steps' in description) {
+      if (Array.isArray(description.steps)) {
+        push(new TypeError(`Wrap steps array in a function`));
+      } else if (typeof description.steps !== 'function') {
+        push(new TypeError(`Expected steps to be a function (returning an array)`));
+      }
+    }
+
+    validateInputs:
+    if ('inputs' in description) {
+      if (
+        Array.isArray(description.inputs) ||
+        typeof description.inputs !== 'object'
+      ) {
+        push(new Error(`Expected inputs to be object, got ${typeAppearance(description.inputs)}`));
+        break validateInputs;
+      }
+
+      nest({message: `Errors in static input descriptions for ${compositionName}`}, ({push}) => {
+        const missingCallsToInput = [];
+        const wrongCallsToInput = [];
+
+        for (const [name, value] of Object.entries(description.inputs)) {
+          if (!isInputToken(value)) {
+            missingCallsToInput.push(name);
+            continue;
+          }
+
+          if (!['input', 'input.staticDependency', 'input.staticValue'].includes(getInputTokenShape(value))) {
+            wrongCallsToInput.push(name);
+          }
+        }
+
+        for (const name of missingCallsToInput) {
+          push(new Error(`${name}: Missing call to input()`));
+        }
+
+        for (const name of wrongCallsToInput) {
+          const shape = getInputTokenShape(description.inputs[name]);
+          push(new Error(`${name}: Expected call to input, input.staticDependency, or input.staticValue, got ${shape}`));
+        }
+      });
+    }
+
+    validateOutputs:
+    if ('outputs' in description) {
+      if (
+        !Array.isArray(description.outputs) &&
+        typeof description.outputs !== 'function'
+      ) {
+        push(new Error(`Expected outputs to be array or function, got ${typeAppearance(description.outputs)}`));
+        break validateOutputs;
+      }
+
+      if (Array.isArray(description.outputs)) {
+        map(
+          description.outputs,
+          decorateErrorWithIndex(value => {
+            if (typeof value !== 'string') {
+              throw new Error(`${value}: Expected string, got ${typeAppearance(value)}`)
+            } else if (!value.startsWith('#')) {
+              throw new Error(`${value}: Expected "#" at start`);
+            }
+          }),
+          {message: `Errors in output descriptions for ${compositionName}`});
+      }
+    }
+  });
+
+  const expectedInputNames =
+    (description.inputs
+      ? Object.keys(description.inputs)
+      : []);
+
+  const instantiate = (inputOptions = {}) => {
+    withAggregate({message: `Errors in input options passed to ${compositionName}`}, ({push}) => {
+      const providedInputNames = Object.keys(inputOptions);
+
+      const misplacedInputNames =
+        providedInputNames
+          .filter(name => !expectedInputNames.includes(name));
+
+      const missingInputNames =
+        expectedInputNames
+          .filter(name => !providedInputNames.includes(name))
+          .filter(name => {
+            const inputDescription = getInputTokenValue(description.inputs[name]);
+            if (!inputDescription) return true;
+            if ('defaultValue' in inputDescription) return false;
+            if ('defaultDependency' in inputDescription) return false;
+            return true;
+          });
+
+      const wrongTypeInputNames = [];
+
+      const expectedStaticValueInputNames = [];
+      const expectedStaticDependencyInputNames = [];
+      const expectedValueProvidingTokenInputNames = [];
+
+      const validateFailedErrors = [];
+
+      for (const [name, value] of Object.entries(inputOptions)) {
+        if (misplacedInputNames.includes(name)) {
+          continue;
+        }
+
+        if (typeof value !== 'string' && !isInputToken(value)) {
+          wrongTypeInputNames.push(name);
+          continue;
+        }
+
+        const descriptionShape = getInputTokenShape(description.inputs[name]);
+
+        const tokenShape = (isInputToken(value) ? getInputTokenShape(value) : null);
+        const tokenValue = (isInputToken(value) ? getInputTokenValue(value) : null);
+
+        switch (descriptionShape) {
+          case'input.staticValue':
+            if (tokenShape !== 'input.value') {
+              expectedStaticValueInputNames.push(name);
+              continue;
+            }
+            break;
+
+          case 'input.staticDependency':
+            if (typeof value !== 'string' && tokenShape !== 'input.dependency') {
+              expectedStaticDependencyInputNames.push(name);
+              continue;
+            }
+            break;
+
+          case 'input':
+            if (typeof value !== 'string' && ![
+              'input',
+              'input.value',
+              'input.dependency',
+              'input.myself',
+              'input.updateValue',
+            ].includes(tokenShape)) {
+              expectedValueProvidingTokenInputNames.push(name);
+              continue;
+            }
+            break;
+        }
+
+        if (tokenShape === 'input.value') {
+          try {
+            validateInputValue(tokenValue, description.inputs[name]);
+          } catch (error) {
+            error.message = `${name}: ${error.message}`;
+            validateFailedErrors.push(error);
+          }
+        }
+      }
+
+      if (!empty(misplacedInputNames)) {
+        push(new Error(`Unexpected input names: ${misplacedInputNames.join(', ')}`));
+      }
+
+      if (!empty(missingInputNames)) {
+        push(new Error(`Required these inputs: ${missingInputNames.join(', ')}`));
+      }
+
+      const inputAppearance = name =>
+        (isInputToken(inputOptions[name])
+          ? `${getInputTokenShape(inputOptions[name])}() call`
+          : `dependency name`);
+
+      for (const name of expectedStaticDependencyInputNames) {
+        const appearance = inputAppearance(name);
+        push(new Error(`${name}: Expected dependency name, got ${appearance}`));
+      }
+
+      for (const name of expectedStaticValueInputNames) {
+        const appearance = inputAppearance(name)
+        push(new Error(`${name}: Expected input.value() call, got ${appearance}`));
+      }
+
+      for (const name of expectedValueProvidingTokenInputNames) {
+        const appearance = getInputTokenShape(inputOptions[name]);
+        push(new Error(`${name}: Expected dependency name or value-providing input() call, got ${appearance}`));
+      }
+
+      for (const name of wrongTypeInputNames) {
+        const type = typeAppearance(inputOptions[name]);
+        push(new Error(`${name}: Expected dependency name or input() call, got ${type}`));
+      }
+
+      for (const error of validateFailedErrors) {
+        push(error);
+      }
+    });
+
+    const inputMetadata = getStaticInputMetadata(inputOptions);
+
+    const expectedOutputNames =
+      (Array.isArray(description.outputs)
+        ? description.outputs
+     : typeof description.outputs === 'function'
+        ? description.outputs(inputMetadata)
+            .map(name =>
+              (name.startsWith('#')
+                ? name
+                : '#' + name))
+        : []);
+
+    const ownUpdateDescription =
+      (typeof description.update === 'object'
+        ? description.update
+     : typeof description.update === 'function'
+        ? description.update(inputMetadata)
+        : null);
+
+    const outputOptions = {};
+
+    const instantiatedTemplate = {
+      symbol: templateCompositeFrom.symbol,
+
+      outputs(providedOptions) {
+        withAggregate({message: `Errors in output options passed to ${compositionName}`}, ({push}) => {
+          const misplacedOutputNames = [];
+          const wrongTypeOutputNames = [];
+
+          for (const [name, value] of Object.entries(providedOptions)) {
+            if (!expectedOutputNames.includes(name)) {
+              misplacedOutputNames.push(name);
+              continue;
+            }
+
+            if (typeof value !== 'string') {
+              wrongTypeOutputNames.push(name);
+              continue;
+            }
+          }
+
+          if (!empty(misplacedOutputNames)) {
+            push(new Error(`Unexpected output names: ${misplacedOutputNames.join(', ')}`));
+          }
+
+          for (const name of wrongTypeOutputNames) {
+            const appearance = typeAppearance(providedOptions[name]);
+            push(new Error(`${name}: Expected string, got ${appearance}`));
+          }
+        });
+
+        Object.assign(outputOptions, providedOptions);
+        return instantiatedTemplate;
+      },
+
+      toDescription() {
+        const finalDescription = {};
+
+        if ('annotation' in description) {
+          finalDescription.annotation = description.annotation;
+        }
+
+        if ('compose' in description) {
+          finalDescription.compose = description.compose;
+        }
+
+        if (ownUpdateDescription) {
+          finalDescription.update = ownUpdateDescription;
+        }
+
+        if ('inputs' in description) {
+          const inputMapping = {};
+
+          for (const [name, token] of Object.entries(description.inputs)) {
+            const tokenValue = getInputTokenValue(token);
+            if (name in inputOptions) {
+              if (typeof inputOptions[name] === 'string') {
+                inputMapping[name] = input.dependency(inputOptions[name]);
+              } else {
+                inputMapping[name] = inputOptions[name];
+              }
+            } else if (tokenValue.defaultValue) {
+              inputMapping[name] = input.value(tokenValue.defaultValue);
+            } else if (tokenValue.defaultDependency) {
+              inputMapping[name] = input.dependency(tokenValue.defaultDependency);
+            } else {
+              inputMapping[name] = input.value(null);
+            }
+          }
+
+          finalDescription.inputMapping = inputMapping;
+          finalDescription.inputDescriptions = description.inputs;
+        }
+
+        if ('outputs' in description) {
+          const finalOutputs = {};
+
+          for (const name of expectedOutputNames) {
+            if (name in outputOptions) {
+              finalOutputs[name] = outputOptions[name];
+            } else {
+              finalOutputs[name] = name;
+            }
+          }
+
+          finalDescription.outputs = finalOutputs;
+        }
+
+        if ('steps' in description) {
+          finalDescription.steps = description.steps;
+        }
+
+        return finalDescription;
+      },
+
+      toResolvedComposition() {
+        const ownDescription = instantiatedTemplate.toDescription();
+
+        const finalDescription = {...ownDescription};
+
+        const aggregate = openAggregate({message: `Errors resolving ${compositionName}`});
+
+        const steps = ownDescription.steps();
+
+        const resolvedSteps =
+          aggregate.map(
+            steps,
+            decorateErrorWithIndex(step =>
+              (step.symbol === templateCompositeFrom.symbol
+                ? compositeFrom(step.toResolvedComposition())
+                : step)),
+            {message: `Errors resolving steps`});
+
+        aggregate.close();
+
+        finalDescription.steps = resolvedSteps;
+
+        return finalDescription;
+      },
+    };
+
+    return instantiatedTemplate;
+  };
+
+  instantiate.inputs = instantiate;
+
+  return instantiate;
+}
+
+templateCompositeFrom.symbol = Symbol();
+
+export const continuationSymbol = Symbol.for('compositeFrom: continuation symbol');
+export const noTransformSymbol = Symbol.for('compositeFrom: no-transform symbol');
+
+export function compositeFrom(description) {
+  const {annotation} = description;
+  const compositionName = getCompositionName(description);
+
+  const debug = fn => {
+    if (compositeFrom.debug === true) {
+      const label =
+        (annotation
+          ? colors.dim(`[composite: ${annotation}]`)
+          : colors.dim(`[composite]`));
+      const result = fn();
+      if (Array.isArray(result)) {
+        console.log(label, ...result.map(value =>
+          (typeof value === 'object'
+            ? inspect(value, {depth: 1, colors: true, compact: true, breakLength: Infinity})
+            : value)));
+      } else {
+        console.log(label, result);
+      }
+    }
+  };
+
+  if (!Array.isArray(description.steps)) {
+    throw new TypeError(
+      `Expected steps to be array, got ${typeAppearance(description.steps)}` +
+      (annotation ? ` (${annotation})` : ''));
+  }
+
+  const composition =
+    description.steps.map(step =>
+      ('toResolvedComposition' in step
+        ? compositeFrom(step.toResolvedComposition())
+        : step));
+
+  const inputMetadata = getStaticInputMetadata(description.inputMapping ?? {});
+
+  function _mapDependenciesToOutputs(providedDependencies) {
+    if (!description.outputs) {
+      return {};
+    }
+
+    if (!providedDependencies) {
+      return {};
+    }
+
+    return (
+      Object.fromEntries(
+        Object.entries(description.outputs)
+          .map(([continuationName, outputName]) => [
+            outputName,
+            (continuationName in providedDependencies
+              ? providedDependencies[continuationName]
+              : providedDependencies[continuationName.replace(/^#/, '')]),
+          ])));
+  }
+
+  // These dependencies were all provided by the composition which this one is
+  // nested inside, so input('name')-shaped tokens are going to be evaluated
+  // in the context of the containing composition.
+  const dependenciesFromInputs =
+    Object.values(description.inputMapping ?? {})
+      .map(token => {
+        const tokenShape = getInputTokenShape(token);
+        const tokenValue = getInputTokenValue(token);
+        switch (tokenShape) {
+          case 'input.dependency':
+            return tokenValue;
+          case 'input':
+          case 'input.updateValue':
+            return token;
+          case 'input.myself':
+            return 'this';
+          default:
+            return null;
+        }
+      })
+      .filter(Boolean);
+
+  const anyInputsUseUpdateValue =
+    dependenciesFromInputs
+      .filter(dependency => isInputToken(dependency))
+      .some(token => getInputTokenShape(token) === 'input.updateValue');
+
+  const inputNames =
+    Object.keys(description.inputMapping ?? {});
+
+  const inputSymbols =
+    inputNames.map(name => input(name));
+
+  const inputsMayBeDynamicValue =
+    stitchArrays({
+      mappingToken: Object.values(description.inputMapping ?? {}),
+      descriptionToken: Object.values(description.inputDescriptions ?? {}),
+    }).map(({mappingToken, descriptionToken}) => {
+        if (getInputTokenShape(descriptionToken) === 'input.staticValue') return false;
+        if (getInputTokenShape(mappingToken) === 'input.value') return false;
+        return true;
+      });
+
+  const inputDescriptions =
+    Object.values(description.inputDescriptions ?? {});
+
+  /*
+  const inputsAcceptNull =
+    Object.values(description.inputDescriptions ?? {})
+      .map(token => {
+        const tokenValue = getInputTokenValue(token);
+        if (!tokenValue) return false;
+        if ('acceptsNull' in tokenValue) return tokenValue.acceptsNull;
+        if ('defaultValue' in tokenValue) return tokenValue.defaultValue === null;
+        return false;
+      });
+  */
+
+  // Update descriptions passed as the value in an input.updateValue() token,
+  // as provided as inputs for this composition.
+  const inputUpdateDescriptions =
+    Object.values(description.inputMapping ?? {})
+      .map(token =>
+        (getInputTokenShape(token) === 'input.updateValue'
+          ? getInputTokenValue(token)
+          : null))
+      .filter(Boolean);
+
+  const base = composition.at(-1);
+  const steps = composition.slice();
+
+  const aggregate = openAggregate({
+    message:
+      `Errors preparing composition` +
+      (annotation ? ` (${annotation})` : ''),
+  });
+
+  const compositionNests = description.compose ?? true;
+
+  // Steps default to exposing if using a shorthand syntax where flags aren't
+  // specified at all.
+  const stepsExpose =
+    steps
+      .map(step =>
+        (step.flags
+          ? step.flags.expose ?? false
+          : true));
+
+  // Steps default to composing if using a shorthand syntax where flags aren't
+  // specified at all - *and* aren't the base (final step), unless the whole
+  // composition is nestable.
+  const stepsCompose =
+    steps
+      .map((step, index, {length}) =>
+        (step.flags
+          ? step.flags.compose ?? false
+          : (index === length - 1
+              ? compositionNests
+              : true)));
+
+  // Steps update if the corresponding flag is explicitly set, if a transform
+  // function is provided, or if the dependencies include an input.updateValue
+  // token.
+  const stepsUpdate =
+    steps
+      .map(step =>
+        (step.flags
+          ? step.flags.update ?? false
+          : !!step.transform ||
+            !!step.dependencies?.some(dependency =>
+                isInputToken(dependency) &&
+                getInputTokenShape(dependency) === 'input.updateValue')));
+
+  // The expose description for a step is just the entire step object, when
+  // using the shorthand syntax where {flags: {expose: true}} is left implied.
+  const stepExposeDescriptions =
+    steps
+      .map((step, index) =>
+        (stepsExpose[index]
+          ? (step.flags
+              ? step.expose ?? null
+              : step)
+          : null));
+
+  // The update description for a step, if present at all, is always set
+  // explicitly. There may be multiple per step - namely that step's own
+  // {update} description, and any descriptions passed as the value in an
+  // input.updateValue({...}) token.
+  const stepUpdateDescriptions =
+    steps
+      .map((step, index) =>
+        (stepsUpdate[index]
+          ? [
+              step.update ?? null,
+              ...(stepExposeDescriptions[index]?.dependencies ?? [])
+                .filter(dependency => isInputToken(dependency))
+                .filter(token => getInputTokenShape(token) === 'input.updateValue')
+                .map(token => getInputTokenValue(token)),
+            ].filter(Boolean)
+          : []));
+
+  // Indicates presence of a {compute} function on the expose description.
+  const stepsCompute =
+    stepExposeDescriptions
+      .map(expose => !!expose?.compute);
+
+  // Indicates presence of a {transform} function on the expose description.
+  const stepsTransform =
+    stepExposeDescriptions
+      .map(expose => !!expose?.transform);
+
+  const dependenciesFromSteps =
+    unique(
+      stepExposeDescriptions
+        .flatMap(expose => expose?.dependencies ?? [])
+        .map(dependency => {
+          if (typeof dependency === 'string')
+            return (dependency.startsWith('#') ? null : dependency);
+
+          const tokenShape = getInputTokenShape(dependency);
+          const tokenValue = getInputTokenValue(dependency);
+          switch (tokenShape) {
+            case 'input.dependency':
+              return (tokenValue.startsWith('#') ? null : tokenValue);
+            case 'input.myself':
+              return 'this';
+            default:
+              return null;
+          }
+        })
+        .filter(Boolean));
+
+  const anyStepsUseUpdateValue =
+    stepExposeDescriptions
+      .some(expose =>
+        (expose?.dependencies
+          ? expose.dependencies.includes(input.updateValue())
+          : false));
+
+  const anyStepsExpose =
+    stepsExpose.includes(true);
+
+  const anyStepsUpdate =
+    stepsUpdate.includes(true);
+
+  const anyStepsCompute =
+    stepsCompute.includes(true);
+
+  const anyStepsTransform =
+    stepsTransform.includes(true);
+
+  const compositionExposes =
+    anyStepsExpose;
+
+  const compositionUpdates =
+    'update' in description ||
+    anyInputsUseUpdateValue ||
+    anyStepsUseUpdateValue ||
+    anyStepsUpdate;
+
+  const stepEntries = stitchArrays({
+    step: steps,
+    stepComposes: stepsCompose,
+    stepComputes: stepsCompute,
+    stepTransforms: stepsTransform,
+  });
+
+  for (let i = 0; i < stepEntries.length; i++) {
+    const {
+      step,
+      stepComposes,
+      stepComputes,
+      stepTransforms,
+    } = stepEntries[i];
+
+    const isBase = i === stepEntries.length - 1;
+    const message =
+      `Errors in step #${i + 1}` +
+      (isBase ? ` (base)` : ``) +
+      (step.annotation ? ` (${step.annotation})` : ``);
+
+    aggregate.nest({message}, ({push}) => {
+      if (isBase && stepComposes !== compositionNests) {
+        return push(new TypeError(
+          (compositionNests
+            ? `Base must compose, this composition is nestable`
+            : `Base must not compose, this composition isn't nestable`)));
+      } else if (!isBase && !stepComposes) {
+        return push(new TypeError(
+          (compositionNests
+            ? `All steps must compose`
+            : `All steps (except base) must compose`)));
+      }
+
+      if (
+        !compositionNests && !compositionUpdates &&
+        stepTransforms && !stepComputes
+      ) {
+        return push(new TypeError(
+          `Steps which only transform can't be used in a composition that doesn't update`));
+      }
+    });
+  }
+
+  if (!compositionNests && !anyStepsCompute && !anyStepsTransform) {
+    aggregate.push(new TypeError(`Expected at least one step to compute or transform`));
+  }
+
+  aggregate.close();
+
+  function _prepareContinuation(callingTransformForThisStep) {
+    const continuationStorage = {
+      returnedWith: null,
+      providedDependencies: undefined,
+      providedValue: undefined,
+    };
+
+    const continuation =
+      (callingTransformForThisStep
+        ? (providedValue, providedDependencies = null) => {
+            continuationStorage.returnedWith = 'continuation';
+            continuationStorage.providedDependencies = providedDependencies;
+            continuationStorage.providedValue = providedValue;
+            return continuationSymbol;
+          }
+        : (providedDependencies = null) => {
+            continuationStorage.returnedWith = 'continuation';
+            continuationStorage.providedDependencies = providedDependencies;
+            return continuationSymbol;
+          });
+
+    continuation.exit = (providedValue) => {
+      continuationStorage.returnedWith = 'exit';
+      continuationStorage.providedValue = providedValue;
+      return continuationSymbol;
+    };
+
+    if (compositionNests) {
+      const makeRaiseLike = returnWith =>
+        (callingTransformForThisStep
+          ? (providedValue, providedDependencies = null) => {
+              continuationStorage.returnedWith = returnWith;
+              continuationStorage.providedDependencies = providedDependencies;
+              continuationStorage.providedValue = providedValue;
+              return continuationSymbol;
+            }
+          : (providedDependencies = null) => {
+              continuationStorage.returnedWith = returnWith;
+              continuationStorage.providedDependencies = providedDependencies;
+              return continuationSymbol;
+            });
+
+      continuation.raiseOutput = makeRaiseLike('raiseOutput');
+      continuation.raiseOutputAbove = makeRaiseLike('raiseOutputAbove');
+    }
+
+    return {continuation, continuationStorage};
+  }
+
+  function _computeOrTransform(initialValue, continuationIfApplicable, initialDependencies) {
+    const expectingTransform = initialValue !== noTransformSymbol;
+
+    let valueSoFar =
+      (expectingTransform
+        ? initialValue
+        : undefined);
+
+    const availableDependencies = {...initialDependencies};
+
+    const inputValues =
+      Object.values(description.inputMapping ?? {})
+        .map(token => {
+          const tokenShape = getInputTokenShape(token);
+          const tokenValue = getInputTokenValue(token);
+          switch (tokenShape) {
+            case 'input.dependency':
+              return initialDependencies[tokenValue];
+            case 'input.value':
+              return tokenValue;
+            case 'input.updateValue':
+              if (!expectingTransform)
+                throw new Error(`Unexpected input.updateValue() accessed on non-transform call`);
+              return valueSoFar;
+            case 'input.myself':
+              return initialDependencies['this'];
+            case 'input':
+              return initialDependencies[token];
+            default:
+              throw new TypeError(`Unexpected input shape ${tokenShape}`);
+          }
+        });
+
+    withAggregate({message: `Errors in input values provided to ${compositionName}`}, ({push}) => {
+      for (const {dynamic, name, value, description} of stitchArrays({
+        dynamic: inputsMayBeDynamicValue,
+        name: inputNames,
+        value: inputValues,
+        description: inputDescriptions,
+      })) {
+        if (!dynamic) continue;
+        try {
+          validateInputValue(value, description);
+        } catch (error) {
+          error.message = `${name}: ${error.message}`;
+          push(error);
+        }
+      }
+    });
+
+    if (expectingTransform) {
+      debug(() => [colors.bright(`begin composition - transforming from:`), initialValue]);
+    } else {
+      debug(() => colors.bright(`begin composition - not transforming`));
+    }
+
+    for (let i = 0; i < steps.length; i++) {
+      const step = steps[i];
+      const isBase = i === steps.length - 1;
+
+      debug(() => [
+        `step #${i+1}` +
+        (isBase
+          ? ` (base):`
+          : ` of ${steps.length}:`),
+        step]);
+
+      const expose =
+        (step.flags
+          ? step.expose
+          : step);
+
+      if (!expose) {
+        if (!isBase) {
+          debug(() => `step #${i+1} - no expose description, nothing to do for this step`);
+          continue;
+        }
+
+        if (expectingTransform) {
+          debug(() => `step #${i+1} (base) - no expose description, returning so-far update value:`, valueSoFar);
+          if (continuationIfApplicable) {
+            debug(() => colors.bright(`end composition - raise (inferred - composing)`));
+            return continuationIfApplicable(valueSoFar);
+          } else {
+            debug(() => colors.bright(`end composition - exit (inferred - not composing)`));
+            return valueSoFar;
+          }
+        } else {
+          debug(() => `step #${i+1} (base) - no expose description, nothing to continue with`);
+          if (continuationIfApplicable) {
+            debug(() => colors.bright(`end composition - raise (inferred - composing)`));
+            return continuationIfApplicable();
+          } else {
+            debug(() => colors.bright(`end composition - exit (inferred - not composing)`));
+            return null;
+          }
+        }
+      }
+
+      const callingTransformForThisStep =
+        expectingTransform && expose.transform;
+
+      let continuationStorage;
+
+      const inputDictionary =
+        Object.fromEntries(
+          stitchArrays({symbol: inputSymbols, value: inputValues})
+            .map(({symbol, value}) => [symbol, value]));
+
+      const filterableDependencies = {
+        ...availableDependencies,
+        ...inputMetadata,
+        ...inputDictionary,
+        ...
+          (expectingTransform
+            ? {[input.updateValue()]: valueSoFar}
+            : {}),
+        [input.myself()]: initialDependencies?.['this'] ?? null,
+      };
+
+      const selectDependencies =
+        (expose.dependencies ?? []).map(dependency => {
+          if (!isInputToken(dependency)) return dependency;
+          const tokenShape = getInputTokenShape(dependency);
+          const tokenValue = getInputTokenValue(dependency);
+          switch (tokenShape) {
+            case 'input':
+            case 'input.staticDependency':
+            case 'input.staticValue':
+              return dependency;
+            case 'input.myself':
+              return input.myself();
+            case 'input.dependency':
+              return tokenValue;
+            case 'input.updateValue':
+              return input.updateValue();
+            default:
+              throw new Error(`Unexpected token ${tokenShape} as dependency`);
+          }
+        })
+
+      const filteredDependencies =
+        filterProperties(filterableDependencies, selectDependencies);
+
+      debug(() => [
+        `step #${i+1} - ${callingTransformForThisStep ? 'transform' : 'compute'}`,
+        `with dependencies:`, filteredDependencies,
+        `selecting:`, selectDependencies,
+        `from available:`, filterableDependencies,
+        ...callingTransformForThisStep ? [`from value:`, valueSoFar] : []]);
+
+      let result;
+
+      const getExpectedEvaluation = () =>
+        (callingTransformForThisStep
+          ? (filteredDependencies
+              ? ['transform', valueSoFar, continuationSymbol, filteredDependencies]
+              : ['transform', valueSoFar, continuationSymbol])
+          : (filteredDependencies
+              ? ['compute', continuationSymbol, filteredDependencies]
+              : ['compute', continuationSymbol]));
+
+      const naturalEvaluate = () => {
+        const [name, ...argsLayout] = getExpectedEvaluation();
+
+        let args;
+
+        if (isBase && !compositionNests) {
+          args =
+            argsLayout.filter(arg => arg !== continuationSymbol);
+        } else {
+          let continuation;
+
+          ({continuation, continuationStorage} =
+            _prepareContinuation(callingTransformForThisStep));
+
+          args =
+            argsLayout.map(arg =>
+              (arg === continuationSymbol
+                ? continuation
+                : arg));
+        }
+
+        return expose[name](...args);
+      }
+
+      switch (step.cache) {
+        // Warning! Highly WIP!
+        case 'aggressive': {
+          const hrnow = () => {
+            const hrTime = process.hrtime();
+            return hrTime[0] * 1000000000 + hrTime[1];
+          };
+
+          const [name, ...args] = getExpectedEvaluation();
+
+          let cache = globalCompositeCache[step.annotation];
+          if (!cache) {
+            cache = globalCompositeCache[step.annotation] = {
+              transform: new TupleMap(),
+              compute: new TupleMap(),
+              times: {
+                read: [],
+                evaluate: [],
+              },
+            };
+          }
+
+          const tuplefied = args
+            .flatMap(arg => [
+              Symbol.for('compositeFrom: tuplefied arg divider'),
+              ...(typeof arg !== 'object' || Array.isArray(arg)
+                ? [arg]
+                : Object.entries(arg).flat()),
+            ]);
+
+          const readTime = hrnow();
+          const cacheContents = cache[name].get(tuplefied);
+          cache.times.read.push(hrnow() - readTime);
+
+          if (cacheContents) {
+            ({result, continuationStorage} = cacheContents);
+          } else {
+            const evaluateTime = hrnow();
+            result = naturalEvaluate();
+            cache.times.evaluate.push(hrnow() - evaluateTime);
+            cache[name].set(tuplefied, {result, continuationStorage});
+          }
+
+          break;
+        }
+
+        default: {
+          result = naturalEvaluate();
+          break;
+        }
+      }
+
+      if (result !== continuationSymbol) {
+        debug(() => [`step #${i+1} - result: exit (inferred) ->`, result]);
+
+        if (compositionNests) {
+          throw new TypeError(`Inferred early-exit is disallowed in nested compositions`);
+        }
+
+        debug(() => colors.bright(`end composition - exit (inferred)`));
+
+        return result;
+      }
+
+      const {returnedWith} = continuationStorage;
+
+      if (returnedWith === 'exit') {
+        const {providedValue} = continuationStorage;
+
+        debug(() => [`step #${i+1} - result: exit (explicit) ->`, providedValue]);
+        debug(() => colors.bright(`end composition - exit (explicit)`));
+
+        if (compositionNests) {
+          return continuationIfApplicable.exit(providedValue);
+        } else {
+          return providedValue;
+        }
+      }
+
+      const {providedValue, providedDependencies} = continuationStorage;
+
+      const continuationArgs = [];
+      if (expectingTransform) {
+        continuationArgs.push(
+          (callingTransformForThisStep
+            ? providedValue ?? null
+            : valueSoFar ?? null));
+      }
+
+      debug(() => {
+        const base = `step #${i+1} - result: ` + returnedWith;
+        const parts = [];
+
+        if (callingTransformForThisStep) {
+          parts.push('value:', providedValue);
+        }
+
+        if (providedDependencies !== null) {
+          parts.push(`deps:`, providedDependencies);
+        } else {
+          parts.push(`(no deps)`);
+        }
+
+        if (empty(parts)) {
+          return base;
+        } else {
+          return [base + ' ->', ...parts];
+        }
+      });
+
+      switch (returnedWith) {
+        case 'raiseOutput':
+          debug(() =>
+            (isBase
+              ? colors.bright(`end composition - raiseOutput (base: explicit)`)
+              : colors.bright(`end composition - raiseOutput`)));
+          continuationArgs.push(_mapDependenciesToOutputs(providedDependencies));
+          return continuationIfApplicable(...continuationArgs);
+
+        case 'raiseOutputAbove':
+          debug(() => colors.bright(`end composition - raiseOutputAbove`));
+          continuationArgs.push(_mapDependenciesToOutputs(providedDependencies));
+          return continuationIfApplicable.raiseOutput(...continuationArgs);
+
+        case 'continuation':
+          if (isBase) {
+            debug(() => colors.bright(`end composition - raiseOutput (inferred)`));
+            continuationArgs.push(_mapDependenciesToOutputs(providedDependencies));
+            return continuationIfApplicable(...continuationArgs);
+          } else {
+            Object.assign(availableDependencies, providedDependencies);
+            if (callingTransformForThisStep && providedValue !== null) {
+              valueSoFar = providedValue;
+            }
+            break;
+          }
+      }
+    }
+  }
+
+  const constructedDescriptor = {};
+
+  if (annotation) {
+    constructedDescriptor.annotation = annotation;
+  }
+
+  constructedDescriptor.flags = {
+    update: compositionUpdates,
+    expose: compositionExposes,
+    compose: compositionNests,
+  };
+
+  if (compositionUpdates) {
+    // TODO: This is a dumb assign statement, and it could probably do more
+    // interesting things, like combining validation functions.
+    constructedDescriptor.update =
+      Object.assign(
+        {...description.update ?? {}},
+        ...inputUpdateDescriptions,
+        ...stepUpdateDescriptions.flat());
+  }
+
+  if (compositionExposes) {
+    const expose = constructedDescriptor.expose = {};
+
+    expose.dependencies =
+      unique([
+        ...dependenciesFromInputs,
+        ...dependenciesFromSteps,
+      ]);
+
+    const _wrapper = (...args) => {
+      try {
+        return _computeOrTransform(...args);
+      } catch (thrownError) {
+        const error = new Error(
+          `Error computing composition` +
+          (annotation ? ` ${annotation}` : ''));
+        error.cause = thrownError;
+        throw error;
+      }
+    };
+
+    if (compositionNests) {
+      if (compositionUpdates) {
+        expose.transform = (value, continuation, dependencies) =>
+          _wrapper(value, continuation, dependencies);
+      }
+
+      if (anyStepsCompute && !anyStepsUseUpdateValue && !anyInputsUseUpdateValue) {
+        expose.compute = (continuation, dependencies) =>
+          _wrapper(noTransformSymbol, continuation, dependencies);
+      }
+
+      if (base.cacheComposition) {
+        expose.cache = base.cacheComposition;
+      }
+    } else if (compositionUpdates) {
+      expose.transform = (value, dependencies) =>
+        _wrapper(value, null, dependencies);
+    } else {
+      expose.compute = (dependencies) =>
+        _wrapper(noTransformSymbol, null, dependencies);
+    }
+  }
+
+  return constructedDescriptor;
+}
+
+export function displayCompositeCacheAnalysis() {
+  const showTimes = (cache, key) => {
+    const times = cache.times[key].slice().sort();
+
+    const all = times;
+    const worst10pc = times.slice(-times.length / 10);
+    const best10pc = times.slice(0, times.length / 10);
+    const middle50pc = times.slice(times.length / 4, -times.length / 4);
+    const middle80pc = times.slice(times.length / 10, -times.length / 10);
+
+    const fmt = val => `${(val / 1000).toFixed(2)}ms`.padStart(9);
+    const avg = times => times.reduce((a, b) => a + b, 0) / times.length;
+
+    const left = ` - ${key}: `;
+    const indn = ' '.repeat(left.length);
+    console.log(left + `${fmt(avg(all))} (all ${all.length})`);
+    console.log(indn + `${fmt(avg(worst10pc))} (worst 10%)`);
+    console.log(indn + `${fmt(avg(best10pc))} (best 10%)`);
+    console.log(indn + `${fmt(avg(middle80pc))} (middle 80%)`);
+    console.log(indn + `${fmt(avg(middle50pc))} (middle 50%)`);
+  };
+
+  for (const [annotation, cache] of Object.entries(globalCompositeCache)) {
+    console.log(`Cached ${annotation}:`);
+    showTimes(cache, 'evaluate');
+    showTimes(cache, 'read');
+  }
+}
+
+// Evaluates a function with composite debugging enabled, turns debugging
+// off again, and returns the result of the function. This is mostly syntax
+// sugar, but also helps avoid unit tests avoid accidentally printing debug
+// info for a bunch of unrelated composites (due to property enumeration
+// when displaying an unexpected result). Use as so:
+//
+//   Without debugging:
+//     t.same(thing.someProp, value)
+//
+//   With debugging:
+//     t.same(debugComposite(() => thing.someProp), value)
+//
+export function debugComposite(fn) {
+  compositeFrom.debug = true;
+  const value = fn();
+  compositeFrom.debug = false;
+  return value;
+}
diff --git a/src/data/things/flash.js b/src/data/things/flash.js
index 6eb5234f..e2afcef4 100644
--- a/src/data/things/flash.js
+++ b/src/data/things/flash.js
@@ -1,25 +1,42 @@
+import {input} from '#composite';
 import find from '#find';
 
+import {
+  isColor,
+  isDirectory,
+  isNumber,
+  isString,
+  oneOf,
+} from '#validators';
+
+import {exposeDependency, exposeUpdateValueOrContinue}
+  from '#composite/control-flow';
+import {withPropertyFromObject} from '#composite/data';
+
+import {
+  color,
+  contributionList,
+  directory,
+  fileExtension,
+  name,
+  referenceList,
+  simpleDate,
+  simpleString,
+  urls,
+  wikiData,
+} from '#composite/wiki-properties';
+
+import {withFlashAct} from '#composite/things/flash';
+
 import Thing from './thing.js';
 
 export class Flash extends Thing {
   static [Thing.referenceType] = 'flash';
 
-  static [Thing.getPropertyDescriptors] = ({
-    Artist,
-    Track,
-    FlashAct,
-
-    validators: {
-      isDirectory,
-      isNumber,
-      isString,
-      oneOf,
-    },
-  }) => ({
+  static [Thing.getPropertyDescriptors] = ({Artist, Track, FlashAct}) => ({
     // Update & expose
 
-    name: Thing.common.name('Unnamed Flash'),
+    name: name('Unnamed Flash'),
 
     directory: {
       flags: {update: true, expose: true},
@@ -47,51 +64,51 @@ export class Flash extends Thing {
       },
     },
 
-    date: Thing.common.simpleDate(),
-
-    coverArtFileExtension: Thing.common.fileExtension('jpg'),
+    color: [
+      exposeUpdateValueOrContinue({
+        validate: input.value(isColor),
+      }),
 
-    contributorContribsByRef: Thing.common.contribsByRef(),
+      withFlashAct(),
 
-    featuredTracksByRef: Thing.common.referenceList(Track),
+      withPropertyFromObject({
+        object: '#flashAct',
+        property: input.value('color'),
+      }),
 
-    urls: Thing.common.urls(),
+      exposeDependency({dependency: '#flashAct.color'}),
+    ],
 
-    // Update only
+    date: simpleDate(),
 
-    artistData: Thing.common.wikiData(Artist),
-    trackData: Thing.common.wikiData(Track),
-    flashActData: Thing.common.wikiData(FlashAct),
+    coverArtFileExtension: fileExtension('jpg'),
 
-    // Expose only
+    contributorContribs: contributionList(),
 
-    contributorContribs: Thing.common.dynamicContribs('contributorContribsByRef'),
+    featuredTracks: referenceList({
+      class: input.value(Track),
+      find: input.value(find.track),
+      data: 'trackData',
+    }),
 
-    featuredTracks: Thing.common.dynamicThingsFromReferenceList(
-      'featuredTracksByRef',
-      'trackData',
-      find.track
-    ),
+    urls: urls(),
 
-    act: {
-      flags: {expose: true},
+    // Update only
 
-      expose: {
-        dependencies: ['flashActData'],
+    artistData: wikiData(Artist),
+    trackData: wikiData(Track),
+    flashActData: wikiData(FlashAct),
 
-        compute: ({flashActData, [Flash.instance]: flash}) =>
-          flashActData.find((act) => act.flashes.includes(flash)) ?? null,
-      },
-    },
+    // Expose only
 
-    color: {
+    act: {
       flags: {expose: true},
 
       expose: {
-        dependencies: ['flashActData'],
+        dependencies: ['this', 'flashActData'],
 
-        compute: ({flashActData, [Flash.instance]: flash}) =>
-          flashActData.find((act) => act.flashes.includes(flash))?.color ?? null,
+        compute: ({this: flash, flashActData}) =>
+          flashActData.find((act) => act.flashes.includes(flash)) ?? null,
       },
     },
   });
@@ -111,17 +128,18 @@ export class Flash extends Thing {
 }
 
 export class FlashAct extends Thing {
-  static [Thing.getPropertyDescriptors] = ({
-    validators: {
-      isColor,
-    },
-  }) => ({
+  static [Thing.referenceType] = 'flash-act';
+  static [Thing.friendlyName] = `Flash Act`;
+
+  static [Thing.getPropertyDescriptors] = () => ({
     // Update & expose
 
-    name: Thing.common.name('Unnamed Flash Act'),
-    color: Thing.common.color(),
-    anchor: Thing.common.simpleString(),
-    jump: Thing.common.simpleString(),
+    name: name('Unnamed Flash Act'),
+    directory: directory(),
+    color: color(),
+    listTerminology: simpleString(),
+
+    jump: simpleString(),
 
     jumpColor: {
       flags: {update: true, expose: true},
@@ -133,18 +151,14 @@ export class FlashAct extends Thing {
       }
     },
 
-    flashesByRef: Thing.common.referenceList(Flash),
+    flashes: referenceList({
+      class: input.value(Flash),
+      find: input.value(find.flash),
+      data: 'flashData',
+    }),
 
     // Update only
 
-    flashData: Thing.common.wikiData(Flash),
-
-    // Expose only
-
-    flashes: Thing.common.dynamicThingsFromReferenceList(
-      'flashesByRef',
-      'flashData',
-      find.flash
-    ),
+    flashData: wikiData(Flash),
   })
 }
diff --git a/src/data/things/group.js b/src/data/things/group.js
index ba339b3e..8764a9db 100644
--- a/src/data/things/group.js
+++ b/src/data/things/group.js
@@ -1,33 +1,44 @@
+import {input} from '#composite';
 import find from '#find';
 
+import {
+  color,
+  directory,
+  name,
+  referenceList,
+  simpleString,
+  urls,
+  wikiData,
+} from '#composite/wiki-properties';
+
 import Thing from './thing.js';
 
 export class Group extends Thing {
   static [Thing.referenceType] = 'group';
 
-  static [Thing.getPropertyDescriptors] = ({
-    Album,
-  }) => ({
+  static [Thing.getPropertyDescriptors] = ({Album}) => ({
     // Update & expose
 
-    name: Thing.common.name('Unnamed Group'),
-    directory: Thing.common.directory(),
+    name: name('Unnamed Group'),
+    directory: directory(),
 
-    description: Thing.common.simpleString(),
+    description: simpleString(),
 
-    urls: Thing.common.urls(),
+    urls: urls(),
 
-    featuredAlbumsByRef: Thing.common.referenceList(Album),
+    featuredAlbums: referenceList({
+      class: input.value(Album),
+      find: input.value(find.album),
+      data: 'albumData',
+    }),
 
     // Update only
 
-    albumData: Thing.common.wikiData(Album),
-    groupCategoryData: Thing.common.wikiData(GroupCategory),
+    albumData: wikiData(Album),
+    groupCategoryData: wikiData(GroupCategory),
 
     // Expose only
 
-    featuredAlbums: Thing.common.dynamicThingsFromReferenceList('featuredAlbumsByRef', 'albumData', find.album),
-
     descriptionShort: {
       flags: {expose: true},
 
@@ -41,8 +52,8 @@ export class Group extends Thing {
       flags: {expose: true},
 
       expose: {
-        dependencies: ['albumData'],
-        compute: ({albumData, [Group.instance]: group}) =>
+        dependencies: ['this', 'albumData'],
+        compute: ({this: group, albumData}) =>
           albumData?.filter((album) => album.groups.includes(group)) ?? [],
       },
     },
@@ -51,9 +62,8 @@ export class Group extends Thing {
       flags: {expose: true},
 
       expose: {
-        dependencies: ['groupCategoryData'],
-
-        compute: ({groupCategoryData, [Group.instance]: group}) =>
+        dependencies: ['this', 'groupCategoryData'],
+        compute: ({this: group, groupCategoryData}) =>
           groupCategoryData.find((category) => category.groups.includes(group))
             ?.color,
       },
@@ -63,8 +73,8 @@ export class Group extends Thing {
       flags: {expose: true},
 
       expose: {
-        dependencies: ['groupCategoryData'],
-        compute: ({groupCategoryData, [Group.instance]: group}) =>
+        dependencies: ['this', 'groupCategoryData'],
+        compute: ({this: group, groupCategoryData}) =>
           groupCategoryData.find((category) => category.groups.includes(group)) ??
           null,
       },
@@ -73,26 +83,22 @@ export class Group extends Thing {
 }
 
 export class GroupCategory extends Thing {
-  static [Thing.getPropertyDescriptors] = ({
-    Group,
-  }) => ({
+  static [Thing.friendlyName] = `Group Category`;
+
+  static [Thing.getPropertyDescriptors] = ({Group}) => ({
     // Update & expose
 
-    name: Thing.common.name('Unnamed Group Category'),
-    color: Thing.common.color(),
+    name: name('Unnamed Group Category'),
+    color: color(),
 
-    groupsByRef: Thing.common.referenceList(Group),
+    groups: referenceList({
+      class: input.value(Group),
+      find: input.value(find.group),
+      data: 'groupData',
+    }),
 
     // Update only
 
-    groupData: Thing.common.wikiData(Group),
-
-    // Expose only
-
-    groups: Thing.common.dynamicThingsFromReferenceList(
-      'groupsByRef',
-      'groupData',
-      find.group
-    ),
+    groupData: wikiData(Group),
   });
 }
diff --git a/src/data/things/homepage-layout.js b/src/data/things/homepage-layout.js
index ec9e9556..bfa971ca 100644
--- a/src/data/things/homepage-layout.js
+++ b/src/data/things/homepage-layout.js
@@ -1,20 +1,37 @@
+import {input} from '#composite';
 import find from '#find';
 
+import {
+  is,
+  isCountingNumber,
+  isString,
+  isStringNonEmpty,
+  oneOf,
+  validateArrayItems,
+  validateInstanceOf,
+  validateReference,
+} from '#validators';
+
+import {exposeDependency} from '#composite/control-flow';
+import {withResolvedReference} from '#composite/wiki-data';
+
+import {
+  color,
+  name,
+  referenceList,
+  simpleString,
+  wikiData,
+} from '#composite/wiki-properties';
+
 import Thing from './thing.js';
 
 export class HomepageLayout extends Thing {
-  static [Thing.getPropertyDescriptors] = ({
-    HomepageLayoutRow,
+  static [Thing.friendlyName] = `Homepage Layout`;
 
-    validators: {
-      isStringNonEmpty,
-      validateArrayItems,
-      validateInstanceOf,
-    },
-  }) => ({
+  static [Thing.getPropertyDescriptors] = ({HomepageLayoutRow}) => ({
     // Update & expose
 
-    sidebarContent: Thing.common.simpleString(),
+    sidebarContent: simpleString(),
 
     navbarLinks: {
       flags: {update: true, expose: true},
@@ -32,13 +49,12 @@ export class HomepageLayout extends Thing {
 }
 
 export class HomepageLayoutRow extends Thing {
-  static [Thing.getPropertyDescriptors] = ({
-    Album,
-    Group,
-  }) => ({
+  static [Thing.friendlyName] = `Homepage Row`;
+
+  static [Thing.getPropertyDescriptors] = ({Album, Group}) => ({
     // Update & expose
 
-    name: Thing.common.name('Unnamed Homepage Row'),
+    name: name('Unnamed Homepage Row'),
 
     type: {
       flags: {update: true, expose: true},
@@ -50,30 +66,22 @@ export class HomepageLayoutRow extends Thing {
       },
     },
 
-    color: Thing.common.color(),
+    color: color(),
 
     // Update only
 
     // These aren't necessarily used by every HomepageLayoutRow subclass, but
     // for convenience of providing this data, every row accepts all wiki data
     // arrays depended upon by any subclass's behavior.
-    albumData: Thing.common.wikiData(Album),
-    groupData: Thing.common.wikiData(Group),
+    albumData: wikiData(Album),
+    groupData: wikiData(Group),
   });
 }
 
 export class HomepageLayoutAlbumsRow extends HomepageLayoutRow {
-  static [Thing.getPropertyDescriptors] = (opts, {
-    Album,
-    Group,
-
-    validators: {
-      is,
-      isCountingNumber,
-      isString,
-      validateArrayItems,
-    },
-  } = opts) => ({
+  static [Thing.friendlyName] = `Homepage Albums Row`;
+
+  static [Thing.getPropertyDescriptors] = (opts, {Album, Group} = opts) => ({
     ...HomepageLayoutRow[Thing.getPropertyDescriptors](opts),
 
     // Update & expose
@@ -104,8 +112,39 @@ export class HomepageLayoutAlbumsRow extends HomepageLayoutRow {
       },
     },
 
-    sourceGroupByRef: Thing.common.singleReference(Group),
-    sourceAlbumsByRef: Thing.common.referenceList(Album),
+    sourceGroup: [
+      {
+        flags: {expose: true, update: true, compose: true},
+
+        update: {
+          validate:
+            oneOf(
+              is('new-releases', 'new-additions'),
+              validateReference(Group[Thing.referenceType])),
+        },
+
+        expose: {
+          transform: (value, continuation) =>
+            (value === 'new-releases' || value === 'new-additions'
+              ? value
+              : continuation(value)),
+        },
+      },
+
+      withResolvedReference({
+        ref: input.updateValue(),
+        data: 'groupData',
+        find: input.value(find.group),
+      }),
+
+      exposeDependency({dependency: '#resolvedReference'}),
+    ],
+
+    sourceAlbums: referenceList({
+      class: input.value(Album),
+      find: input.value(find.album),
+      data: 'albumData',
+    }),
 
     countAlbumsFromGroup: {
       flags: {update: true, expose: true},
@@ -116,19 +155,5 @@ export class HomepageLayoutAlbumsRow extends HomepageLayoutRow {
       flags: {update: true, expose: true},
       update: {validate: validateArrayItems(isString)},
     },
-
-    // Expose only
-
-    sourceGroup: Thing.common.dynamicThingFromSingleReference(
-      'sourceGroupByRef',
-      'groupData',
-      find.group
-    ),
-
-    sourceAlbums: Thing.common.dynamicThingsFromReferenceList(
-      'sourceAlbumsByRef',
-      'albumData',
-      find.album
-    ),
   });
 }
diff --git a/src/data/things/index.js b/src/data/things/index.js
index 591cdc3b..4ea1f007 100644
--- a/src/data/things/index.js
+++ b/src/data/things/index.js
@@ -2,9 +2,9 @@ import * as path from 'node:path';
 import {fileURLToPath} from 'node:url';
 
 import {logError} from '#cli';
+import {compositeFrom} from '#composite';
 import * as serialize from '#serialize';
 import {openAggregate, showAggregate} from '#sugar';
-import * as validators from '#validators';
 
 import Thing from './thing.js';
 
@@ -21,7 +21,11 @@ import * as trackClasses from './track.js';
 import * as wikiInfoClasses from './wiki-info.js';
 
 export {default as Thing} from './thing.js';
-export {default as CacheableObject} from './cacheable-object.js';
+
+export {
+  default as CacheableObject,
+  CacheableObjectPropertyValueError,
+} from './cacheable-object.js';
 
 const allClassLists = {
   'album.js': albumClasses,
@@ -82,6 +86,8 @@ function errorDuplicateClassNames() {
 function flattenClassLists() {
   for (const classes of Object.values(allClassLists)) {
     for (const [name, constructor] of Object.entries(classes)) {
+      if (typeof constructor !== 'function') continue;
+      if (!(constructor.prototype instanceof Thing)) continue;
       allClasses[name] = constructor;
     }
   }
@@ -119,7 +125,7 @@ function descriptorAggregateHelper({
 }
 
 function evaluatePropertyDescriptors() {
-  const opts = {...allClasses, validators};
+  const opts = {...allClasses};
 
   return descriptorAggregateHelper({
     message: `Errors evaluating Thing class property descriptors`,
@@ -129,8 +135,21 @@ function evaluatePropertyDescriptors() {
         throw new Error(`Missing [Thing.getPropertyDescriptors] function`);
       }
 
-      constructor.propertyDescriptors =
-        constructor[Thing.getPropertyDescriptors](opts);
+      const results = constructor[Thing.getPropertyDescriptors](opts);
+
+      for (const [key, value] of Object.entries(results)) {
+        if (Array.isArray(value)) {
+          results[key] = compositeFrom({
+            annotation: `${constructor.name}.${key}`,
+            compose: false,
+            steps: value,
+          });
+        } else if (value.toResolvedComposition) {
+          results[key] = compositeFrom(value.toResolvedComposition());
+        }
+      }
+
+      constructor.propertyDescriptors = results;
     },
 
     showFailedClasses(failedClasses) {
diff --git a/src/data/things/language.js b/src/data/things/language.js
index 7755c505..646eb6d1 100644
--- a/src/data/things/language.js
+++ b/src/data/things/language.js
@@ -1,11 +1,17 @@
+import {Tag} from '#html';
+import {isLanguageCode} from '#validators';
+
+import {
+  externalFunction,
+  flag,
+  simpleString,
+} from '#composite/wiki-properties';
+
+import CacheableObject from './cacheable-object.js';
 import Thing from './thing.js';
 
 export class Language extends Thing {
-  static [Thing.getPropertyDescriptors] = ({
-    validators: {
-      isLanguageCode,
-    },
-  }) => ({
+  static [Thing.getPropertyDescriptors] = () => ({
     // Update & expose
 
     // General language code. This is used to identify the language distinctly
@@ -18,7 +24,7 @@ export class Language extends Thing {
 
     // Human-readable name. This should be the language's own native name, not
     // localized to any other language.
-    name: Thing.common.simpleString(),
+    name: simpleString(),
 
     // Language code specific to JavaScript's Internationalization (Intl) API.
     // Usually this will be the same as the language's general code, but it
@@ -40,7 +46,7 @@ export class Language extends Thing {
     // with languages that are currently in development and not ready for
     // formal release, or which are just kept hidden as "experimental zones"
     // for wiki development or content testing.
-    hidden: Thing.common.flag(false),
+    hidden: flag(false),
 
     // Mapping of translation keys to values (strings). Generally, don't
     // access this object directly - use methods instead.
@@ -68,7 +74,7 @@ export class Language extends Thing {
 
     // Update only
 
-    escapeHTML: Thing.common.externalFunction(),
+    escapeHTML: externalFunction(),
 
     // Expose only
 
@@ -95,6 +101,7 @@ export class Language extends Thing {
       },
     },
 
+    // TODO: This currently isn't used. Is it still needed?
     strings_htmlEscaped: {
       flags: {expose: true},
       expose: {
@@ -124,8 +131,8 @@ export class Language extends Thing {
     };
   }
 
-  $(key, args = {}) {
-    return this.formatString(key, args);
+  $(...args) {
+    return this.formatString(...args);
   }
 
   assertIntlAvailable(property) {
@@ -139,20 +146,22 @@ export class Language extends Thing {
     return this.intl_pluralCardinal.select(value);
   }
 
-  formatString(key, args = {}) {
-    if (this.strings && !this.strings_htmlEscaped) {
-      throw new Error(`HTML-escaped strings unavailable - please ensure escapeHTML function is provided`);
-    }
+  formatString(...args) {
+    const hasOptions =
+      typeof args.at(-1) === 'object' &&
+      args.at(-1) !== null;
 
-    return this.formatStringHelper(this.strings_htmlEscaped, key, args);
-  }
+    const key =
+      (hasOptions ? args.slice(0, -1) : args)
+        .filter(Boolean)
+        .join('.');
 
-  formatStringNoHTMLEscape(key, args = {}) {
-    return this.formatStringHelper(this.strings, key, args);
-  }
+    const options =
+      (hasOptions
+        ? args.at(-1)
+        : null);
 
-  formatStringHelper(strings, key, args = {}) {
-    if (!strings) {
+    if (!this.strings) {
       throw new Error(`Strings unavailable`);
     }
 
@@ -160,30 +169,94 @@ export class Language extends Thing {
       throw new Error(`Invalid key ${key} accessed`);
     }
 
-    const template = strings[key];
-
-    // Convert the keys on the args dict from camelCase to CONSTANT_CASE.
-    // (This isn't an OUTRAGEOUSLY versatile algorithm for doing that, 8ut
-    // like, who cares, dude?) Also, this is an array, 8ecause it's handy
-    // for the iterating we're a8out to do.
-    const processedArgs = Object.entries(args).map(([k, v]) => [
-      k.replace(/[A-Z]/g, '_$&').toUpperCase(),
-      v,
-    ]);
-
-    // Replacement time! Woot. Reduce comes in handy here!
-    const output = processedArgs.reduce(
-      (x, [k, v]) => x.replaceAll(`{${k}}`, v),
-      template
-    );
+    const template = this.strings[key];
+
+    let output;
+
+    if (hasOptions) {
+      // Convert the keys on the options dict from camelCase to CONSTANT_CASE.
+      // (This isn't an OUTRAGEOUSLY versatile algorithm for doing that, 8ut
+      // like, who cares, dude?) Also, this is an array, 8ecause it's handy
+      // for the iterating we're a8out to do. Also strip HTML from arguments
+      // that are literal strings - real HTML content should always be proper
+      // HTML objects (see html.js).
+      const processedOptions =
+        Object.entries(options).map(([k, v]) => [
+          k.replace(/[A-Z]/g, '_$&').toUpperCase(),
+          this.#sanitizeStringArg(v),
+        ]);
+
+      // Replacement time! Woot. Reduce comes in handy here!
+      output =
+        processedOptions.reduce(
+          (x, [k, v]) => x.replaceAll(`{${k}}`, v),
+          template);
+    } else {
+      // Without any options provided, just use the template as-is. This will
+      // still error if the template expected arguments, and otherwise will be
+      // the right value.
+      output = template;
+    }
 
     // Post-processing: if any expected arguments *weren't* replaced, that
     // is almost definitely an error.
-    if (output.match(/\{[A-Z_]+\}/)) {
+    if (output.match(/\{[A-Z][A-Z0-9_]*\}/)) {
       throw new Error(`Args in ${key} were missing - output: ${output}`);
     }
 
-    return output;
+    // Last caveat: Wrap the output in an HTML tag so that it doesn't get
+    // treated as unsanitized HTML if *it* gets passed as an argument to
+    // *another* formatString call.
+    return this.#wrapSanitized(output);
+  }
+
+  // Escapes HTML special characters so they're displayed as-are instead of
+  // treated by the browser as a tag. This does *not* have an effect on actual
+  // html.Tag objects, which are treated as sanitized by default (so that they
+  // can be nested inside strings at all).
+  #sanitizeStringArg(arg) {
+    const escapeHTML = CacheableObject.getUpdateValue(this, 'escapeHTML');
+
+    if (!escapeHTML) {
+      throw new Error(`escapeHTML unavailable`);
+    }
+
+    if (typeof arg !== 'string') {
+      return arg.toString();
+    }
+
+    return escapeHTML(arg);
+  }
+
+  // Wraps the output of a formatting function in a no-name-nor-attributes
+  // HTML tag, which will indicate to other calls to formatString that this
+  // content is a string *that may contain HTML* and doesn't need to
+  // sanitized any further. It'll still .toString() to just the string
+  // contents, if needed.
+  #wrapSanitized(output) {
+    return new Tag(null, null, output);
+  }
+
+  // Similar to the above internal methods, but this one is public.
+  // It should be used when embedding content that may not have previously
+  // been sanitized directly into an HTML tag or template's contents.
+  // The templating engine usually handles this on its own, as does passing
+  // a value (sanitized or not) directly as an argument to formatString,
+  // but if you used a custom validation function ({validate: v => v.isHTML}
+  // instead of {type: 'string'} / {type: 'html'}) and are embedding the
+  // contents of a slot directly, it should be manually sanitized with this
+  // function first.
+  sanitize(arg) {
+    const escapeHTML = CacheableObject.getUpdateValue(this, 'escapeHTML');
+
+    if (!escapeHTML) {
+      throw new Error(`escapeHTML unavailable`);
+    }
+
+    return (
+      (typeof arg === 'string'
+        ? new Tag(null, null, escapeHTML(arg))
+        : arg));
   }
 
   formatDate(date) {
@@ -252,19 +325,32 @@ export class Language extends Thing {
   // Conjunction list: A, B, and C
   formatConjunctionList(array) {
     this.assertIntlAvailable('intl_listConjunction');
-    return this.intl_listConjunction.format(array.map(arr => arr.toString()));
+    return this.#wrapSanitized(
+      this.intl_listConjunction.format(
+        array.map(item => this.#sanitizeStringArg(item))));
   }
 
   // Disjunction lists: A, B, or C
   formatDisjunctionList(array) {
     this.assertIntlAvailable('intl_listDisjunction');
-    return this.intl_listDisjunction.format(array.map(arr => arr.toString()));
+    return this.#wrapSanitized(
+      this.intl_listDisjunction.format(
+        array.map(item => this.#sanitizeStringArg(item))));
   }
 
   // Unit lists: A, B, C
   formatUnitList(array) {
     this.assertIntlAvailable('intl_listUnit');
-    return this.intl_listUnit.format(array.map(arr => arr.toString()));
+    return this.#wrapSanitized(
+      this.intl_listUnit.format(
+        array.map(item => this.#sanitizeStringArg(item))));
+  }
+
+  // Lists without separator: A B C
+  formatListWithoutSeparator(array) {
+    return this.#wrapSanitized(
+      array.map(item => this.#sanitizeStringArg(item))
+        .join(' '));
   }
 
   // File sizes: 42.5 kB, 127.2 MB, 4.13 GB, 998.82 TB
diff --git a/src/data/things/news-entry.js b/src/data/things/news-entry.js
index 43911410..36da0299 100644
--- a/src/data/things/news-entry.js
+++ b/src/data/things/news-entry.js
@@ -1,16 +1,24 @@
+import {
+  directory,
+  name,
+  simpleDate,
+  simpleString,
+} from '#composite/wiki-properties';
+
 import Thing from './thing.js';
 
 export class NewsEntry extends Thing {
   static [Thing.referenceType] = 'news-entry';
+  static [Thing.friendlyName] = `News Entry`;
 
   static [Thing.getPropertyDescriptors] = () => ({
     // Update & expose
 
-    name: Thing.common.name('Unnamed News Entry'),
-    directory: Thing.common.directory(),
-    date: Thing.common.simpleDate(),
+    name: name('Unnamed News Entry'),
+    directory: directory(),
+    date: simpleDate(),
 
-    content: Thing.common.simpleString(),
+    content: simpleString(),
 
     // Expose only
 
diff --git a/src/data/things/static-page.js b/src/data/things/static-page.js
index 3d8d474c..ab9c5f98 100644
--- a/src/data/things/static-page.js
+++ b/src/data/things/static-page.js
@@ -1,16 +1,21 @@
+import {isName} from '#validators';
+
+import {
+  directory,
+  name,
+  simpleString,
+} from '#composite/wiki-properties';
+
 import Thing from './thing.js';
 
 export class StaticPage extends Thing {
   static [Thing.referenceType] = 'static';
+  static [Thing.friendlyName] = `Static Page`;
 
-  static [Thing.getPropertyDescriptors] = ({
-    validators: {
-      isName,
-    },
-  }) => ({
+  static [Thing.getPropertyDescriptors] = () => ({
     // Update & expose
 
-    name: Thing.common.name('Unnamed Static Page'),
+    name: name('Unnamed Static Page'),
 
     nameShort: {
       flags: {update: true, expose: true},
@@ -22,8 +27,8 @@ export class StaticPage extends Thing {
       },
     },
 
-    directory: Thing.common.directory(),
-    content: Thing.common.simpleString(),
-    stylesheet: Thing.common.simpleString(),
+    directory: directory(),
+    content: simpleString(),
+    stylesheet: simpleString(),
   });
 }
diff --git a/src/data/things/thing.js b/src/data/things/thing.js
index c2876f56..def7e914 100644
--- a/src/data/things/thing.js
+++ b/src/data/things/thing.js
@@ -1,399 +1,19 @@
-// Thing: base class for wiki data types, providing wiki-specific utility
-// functions on top of essential CacheableObject behavior.
+// Thing: base class for wiki data types, providing interfaces generally useful
+// to all wiki data objects on top of foundational CacheableObject behavior.
 
 import {inspect} from 'node:util';
 
-import {color} from '#cli';
-import find from '#find';
-import {empty} from '#sugar';
-import {getKebabCase} from '#wiki-data';
-
-import {
-  isAdditionalFileList,
-  isBoolean,
-  isCommentary,
-  isColor,
-  isContributionList,
-  isDate,
-  isDirectory,
-  isFileExtension,
-  isName,
-  isString,
-  isURL,
-  validateArrayItems,
-  validateInstanceOf,
-  validateReference,
-  validateReferenceList,
-} from '#validators';
+import {colors} from '#cli';
 
 import CacheableObject from './cacheable-object.js';
 
 export default class Thing extends CacheableObject {
-  static referenceType = Symbol('Thing.referenceType');
+  static referenceType = Symbol.for('Thing.referenceType');
+  static friendlyName = Symbol.for(`Thing.friendlyName`);
 
   static getPropertyDescriptors = Symbol('Thing.getPropertyDescriptors');
   static getSerializeDescriptors = Symbol('Thing.getSerializeDescriptors');
 
-  // Regularly reused property descriptors, for ease of access and generally
-  // duplicating less code across wiki data types. These are specialized utility
-  // functions, so check each for how its own arguments behave!
-  static common = {
-    name: (defaultName) => ({
-      flags: {update: true, expose: true},
-      update: {validate: isName, default: defaultName},
-    }),
-
-    color: () => ({
-      flags: {update: true, expose: true},
-      update: {validate: isColor},
-    }),
-
-    directory: () => ({
-      flags: {update: true, expose: true},
-      update: {validate: isDirectory},
-      expose: {
-        dependencies: ['name'],
-        transform(directory, {name}) {
-          if (directory === null && name === null) return null;
-          else if (directory === null) return getKebabCase(name);
-          else return directory;
-        },
-      },
-    }),
-
-    urls: () => ({
-      flags: {update: true, expose: true},
-      update: {validate: validateArrayItems(isURL)},
-      expose: {transform: (value) => value ?? []},
-    }),
-
-    // A file extension! Or the default, if provided when calling this.
-    fileExtension: (defaultFileExtension = null) => ({
-      flags: {update: true, expose: true},
-      update: {validate: isFileExtension},
-      expose: {transform: (value) => value ?? defaultFileExtension},
-    }),
-
-    // Straightforward flag descriptor for a variety of property purposes.
-    // Provide a default value, true or false!
-    flag: (defaultValue = false) => {
-      if (typeof defaultValue !== 'boolean') {
-        throw new TypeError(`Always set explicit defaults for flags!`);
-      }
-
-      return {
-        flags: {update: true, expose: true},
-        update: {validate: isBoolean, default: defaultValue},
-      };
-    },
-
-    // General date type, used as the descriptor for a bunch of properties.
-    // This isn't dynamic though - it won't inherit from a date stored on
-    // another object, for example.
-    simpleDate: () => ({
-      flags: {update: true, expose: true},
-      update: {validate: isDate},
-    }),
-
-    // General string type. This should probably generally be avoided in favor
-    // of more specific validation, but using it makes it easy to find where we
-    // might want to improve later, and it's a useful shorthand meanwhile.
-    simpleString: () => ({
-      flags: {update: true, expose: true},
-      update: {validate: isString},
-    }),
-
-    // External function. These should only be used as dependencies for other
-    // properties, so they're left unexposed.
-    externalFunction: () => ({
-      flags: {update: true},
-      update: {validate: (t) => typeof t === 'function'},
-    }),
-
-    // Super simple "contributions by reference" list, used for a variety of
-    // properties (Artists, Cover Artists, etc). This is the property which is
-    // externally provided, in the form:
-    //
-    //     [
-    //         {who: 'Artist Name', what: 'Viola'},
-    //         {who: 'artist:john-cena', what: null},
-    //         ...
-    //     ]
-    //
-    // ...processed from YAML, spreadsheet, or any other kind of input.
-    contribsByRef: () => ({
-      flags: {update: true, expose: true},
-      update: {validate: isContributionList},
-    }),
-
-    // Artist commentary! Generally present on tracks and albums.
-    commentary: () => ({
-      flags: {update: true, expose: true},
-      update: {validate: isCommentary},
-    }),
-
-    // This is a somewhat more involved data structure - it's for additional
-    // or "bonus" files associated with albums or tracks (or anything else).
-    // It's got this form:
-    //
-    //     [
-    //         {title: 'Booklet', files: ['Booklet.pdf']},
-    //         {
-    //             title: 'Wallpaper',
-    //             description: 'Cool Wallpaper!',
-    //             files: ['1440x900.png', '1920x1080.png']
-    //         },
-    //         {title: 'Alternate Covers', description: null, files: [...]},
-    //         ...
-    //     ]
-    //
-    additionalFiles: () => ({
-      flags: {update: true, expose: true},
-      update: {validate: isAdditionalFileList},
-      expose: {
-        transform: (additionalFiles) =>
-          additionalFiles ?? [],
-      },
-    }),
-
-    // A reference list! Keep in mind this is for general references to wiki
-    // objects of (usually) other Thing subclasses, not specifically leitmotif
-    // references in tracks (although that property uses referenceList too!).
-    //
-    // The underlying function validateReferenceList expects a string like
-    // 'artist' or 'track', but this utility keeps from having to hard-code the
-    // string in multiple places by referencing the value saved on the class
-    // instead.
-    referenceList: (thingClass) => {
-      const {[Thing.referenceType]: referenceType} = thingClass;
-      if (!referenceType) {
-        throw new Error(`The passed constructor ${thingClass.name} doesn't define Thing.referenceType!`);
-      }
-
-      return {
-        flags: {update: true, expose: true},
-        update: {validate: validateReferenceList(referenceType)},
-      };
-    },
-
-    // Corresponding function for a single reference.
-    singleReference: (thingClass) => {
-      const {[Thing.referenceType]: referenceType} = thingClass;
-      if (!referenceType) {
-        throw new Error(`The passed constructor ${thingClass.name} doesn't define Thing.referenceType!`);
-      }
-
-      return {
-        flags: {update: true, expose: true},
-        update: {validate: validateReference(referenceType)},
-      };
-    },
-
-    // Corresponding dynamic property to referenceList, which takes the values
-    // in the provided property and searches the specified wiki data for
-    // matching actual Thing-subclass objects.
-    dynamicThingsFromReferenceList: (
-      referenceListProperty,
-      thingDataProperty,
-      findFn
-    ) => ({
-      flags: {expose: true},
-
-      expose: {
-        dependencies: [referenceListProperty, thingDataProperty],
-        compute: ({
-          [referenceListProperty]: refs,
-          [thingDataProperty]: thingData,
-        }) =>
-          refs && thingData
-            ? refs
-                .map((ref) => findFn(ref, thingData, {mode: 'quiet'}))
-                .filter(Boolean)
-            : [],
-      },
-    }),
-
-    // Corresponding function for a single reference.
-    dynamicThingFromSingleReference: (
-      singleReferenceProperty,
-      thingDataProperty,
-      findFn
-    ) => ({
-      flags: {expose: true},
-
-      expose: {
-        dependencies: [singleReferenceProperty, thingDataProperty],
-        compute: ({
-          [singleReferenceProperty]: ref,
-          [thingDataProperty]: thingData,
-        }) => (ref && thingData ? findFn(ref, thingData, {mode: 'quiet'}) : null),
-      },
-    }),
-
-    // Corresponding dynamic property to contribsByRef, which takes the values
-    // in the provided property and searches the object's artistData for
-    // matching actual Artist objects. The computed structure has the same form
-    // as contribsByRef, but with Artist objects instead of string references:
-    //
-    //     [
-    //         {who: (an Artist), what: 'Viola'},
-    //         {who: (an Artist), what: null},
-    //         ...
-    //     ]
-    //
-    // Contributions whose "who" values don't match anything in artistData are
-    // filtered out. (So if the list is all empty, chances are that either the
-    // reference list is somehow messed up, or artistData isn't being provided
-    // properly.)
-    dynamicContribs: (contribsByRefProperty) => ({
-      flags: {expose: true},
-      expose: {
-        dependencies: ['artistData', contribsByRefProperty],
-        compute: ({artistData, [contribsByRefProperty]: contribsByRef}) =>
-          contribsByRef && artistData
-            ? contribsByRef
-                .map(({who: ref, what}) => ({
-                  who: find.artist(ref, artistData),
-                  what,
-                }))
-                .filter(({who}) => who)
-            : [],
-      },
-    }),
-
-    // Dynamically inherit a contribution list from some other object, if it
-    // hasn't been overridden on this object. This is handy for solo albums
-    // where all tracks have the same artist, for example.
-    dynamicInheritContribs: (
-      // If this property is explicitly false, the contribution list returned
-      // will always be empty.
-      nullerProperty,
-
-      // Property holding contributions on the current object.
-      contribsByRefProperty,
-
-      // Property holding corresponding "default" contributions on the parent
-      // object, which will fallen back to if the object doesn't have its own
-      // contribs.
-      parentContribsByRefProperty,
-
-      // Data array to search in and "find" function to locate parent object
-      // (which will be passed the child object and the wiki data array).
-      thingDataProperty,
-      findFn
-    ) => ({
-      flags: {expose: true},
-      expose: {
-        dependencies: [
-          contribsByRefProperty,
-          thingDataProperty,
-          nullerProperty,
-          'artistData',
-        ].filter(Boolean),
-
-        compute({
-          [Thing.instance]: thing,
-          [nullerProperty]: nuller,
-          [contribsByRefProperty]: contribsByRef,
-          [thingDataProperty]: thingData,
-          artistData,
-        }) {
-          if (!artistData) return [];
-          if (nuller === false) return [];
-          const refs =
-            contribsByRef ??
-            findFn(thing, thingData, {mode: 'quiet'})?.[parentContribsByRefProperty];
-          if (!refs) return [];
-          return refs
-            .map(({who: ref, what}) => ({
-              who: find.artist(ref, artistData),
-              what,
-            }))
-            .filter(({who}) => who);
-        },
-      },
-    }),
-
-    // Nice 'n simple shorthand for an exposed-only flag which is true when any
-    // contributions are present in the specified property.
-    contribsPresent: (contribsByRefProperty) => ({
-      flags: {expose: true},
-      expose: {
-        dependencies: [contribsByRefProperty],
-        compute({
-          [contribsByRefProperty]: contribsByRef,
-        }) {
-          return !empty(contribsByRef);
-        },
-      }
-    }),
-
-    // Neat little shortcut for "reversing" the reference lists stored on other
-    // things - for example, tracks specify a "referenced tracks" property, and
-    // you would use this to compute a corresponding "referenced *by* tracks"
-    // property. Naturally, the passed ref list property is of the things in the
-    // wiki data provided, not the requesting Thing itself.
-    reverseReferenceList: (thingDataProperty, referencerRefListProperty) => ({
-      flags: {expose: true},
-
-      expose: {
-        dependencies: [thingDataProperty],
-
-        compute: ({[thingDataProperty]: thingData, [Thing.instance]: thing}) =>
-          thingData?.filter(t => t[referencerRefListProperty].includes(thing)) ?? [],
-      },
-    }),
-
-    // Corresponding function for single references. Note that the return value
-    // is still a list - this is for matching all the objects whose single
-    // reference (in the given property) matches this Thing.
-    reverseSingleReference: (thingDataProperty, referencerRefListProperty) => ({
-      flags: {expose: true},
-
-      expose: {
-        dependencies: [thingDataProperty],
-
-        compute: ({[thingDataProperty]: thingData, [Thing.instance]: thing}) =>
-          thingData?.filter((t) => t[referencerRefListProperty] === thing) ?? [],
-      },
-    }),
-
-    // General purpose wiki data constructor, for properties like artistData,
-    // trackData, etc.
-    wikiData: (thingClass) => ({
-      flags: {update: true},
-      update: {
-        validate: validateArrayItems(validateInstanceOf(thingClass)),
-      },
-    }),
-
-    // This one's kinda tricky: it parses artist "references" from the
-    // commentary content, and finds the matching artist for each reference.
-    // This is mostly useful for credits and listings on artist pages.
-    commentatorArtists: () => ({
-      flags: {expose: true},
-
-      expose: {
-        dependencies: ['artistData', 'commentary'],
-
-        compute: ({artistData, commentary}) =>
-          artistData && commentary
-            ? Array.from(
-                new Set(
-                  Array.from(
-                    commentary
-                      .replace(/<\/?b>/g, '')
-                      .matchAll(/<i>(?<who>.*?):<\/i>/g)
-                  ).map(({groups: {who}}) =>
-                    find.artist(who, artistData, {mode: 'quiet'})
-                  )
-                )
-              )
-            : [],
-      },
-    }),
-  };
-
   // Default custom inspect function, which may be overridden by Thing
   // subclasses. This will be used when displaying aggregate errors and other
   // command-line logging - it's the place to provide information useful in
@@ -402,8 +22,8 @@ export default class Thing extends CacheableObject {
     const cname = this.constructor.name;
 
     return (
-      (this.name ? `${cname} ${color.green(`"${this.name}"`)}` : `${cname}`) +
-      (this.directory ? ` (${color.blue(Thing.getReference(this))})` : '')
+      (this.name ? `${cname} ${colors.green(`"${this.name}"`)}` : `${cname}`) +
+      (this.directory ? ` (${colors.blue(Thing.getReference(this))})` : '')
     );
   }
 
diff --git a/src/data/things/track.js b/src/data/things/track.js
index e176acb4..db325a17 100644
--- a/src/data/things/track.js
+++ b/src/data/things/track.js
@@ -1,460 +1,330 @@
 import {inspect} from 'node:util';
 
-import {color} from '#cli';
+import {colors} from '#cli';
+import {input} from '#composite';
 import find from '#find';
-import {empty} from '#sugar';
 
+import {
+  isColor,
+  isContributionList,
+  isDate,
+  isFileExtension,
+} from '#validators';
+
+import {withPropertyFromObject} from '#composite/data';
+import {withResolvedContribs} from '#composite/wiki-data';
+
+import {
+  exitWithoutDependency,
+  exposeConstant,
+  exposeDependency,
+  exposeDependencyOrContinue,
+  exposeUpdateValueOrContinue,
+} from '#composite/control-flow';
+
+import {
+  additionalFiles,
+  commentary,
+  commentatorArtists,
+  contributionList,
+  directory,
+  duration,
+  flag,
+  name,
+  referenceList,
+  reverseReferenceList,
+  simpleDate,
+  singleReference,
+  simpleString,
+  urls,
+  wikiData,
+} from '#composite/wiki-properties';
+
+import {
+  exitWithoutUniqueCoverArt,
+  inheritFromOriginalRelease,
+  trackReverseReferenceList,
+  withAlbum,
+  withAlwaysReferenceByDirectory,
+  withContainingTrackSection,
+  withHasUniqueCoverArt,
+  withOtherReleases,
+  withPropertyFromAlbum,
+} from '#composite/things/track';
+
+import CacheableObject from './cacheable-object.js';
 import Thing from './thing.js';
 
 export class Track extends Thing {
   static [Thing.referenceType] = 'track';
 
-  static [Thing.getPropertyDescriptors] = ({
-    Album,
-    ArtTag,
-    Artist,
-    Flash,
-
-    validators: {
-      isBoolean,
-      isColor,
-      isDate,
-      isDuration,
-      isFileExtension,
-    },
-  }) => ({
+  static [Thing.getPropertyDescriptors] = ({Album, ArtTag, Artist, Flash}) => ({
     // Update & expose
 
-    name: Thing.common.name('Unnamed Track'),
-    directory: Thing.common.directory(),
-
-    duration: {
-      flags: {update: true, expose: true},
-      update: {validate: isDuration},
-    },
-
-    urls: Thing.common.urls(),
-    dateFirstReleased: Thing.common.simpleDate(),
-
-    artistContribsByRef: Thing.common.contribsByRef(),
-    contributorContribsByRef: Thing.common.contribsByRef(),
-    coverArtistContribsByRef: Thing.common.contribsByRef(),
-
-    referencedTracksByRef: Thing.common.referenceList(Track),
-    sampledTracksByRef: Thing.common.referenceList(Track),
-    artTagsByRef: Thing.common.referenceList(ArtTag),
-
-    hasCoverArt: {
-      flags: {update: true, expose: true},
-
-      update: {
-        validate(value) {
-          if (value !== false) {
-            throw new TypeError(`Expected false or null`);
-          }
-
-          return true;
-        },
-      },
-
-      expose: {
-        dependencies: ['albumData', 'coverArtistContribsByRef'],
-        transform: (hasCoverArt, {
-          albumData,
-          coverArtistContribsByRef,
-          [Track.instance]: track,
-        }) =>
-          Track.hasCoverArt(
-            track,
-            albumData,
-            coverArtistContribsByRef,
-            hasCoverArt
-          ),
-      },
-    },
-
-    coverArtFileExtension: {
-      flags: {update: true, expose: true},
-
-      update: {validate: isFileExtension},
-
-      expose: {
-        dependencies: ['albumData', 'coverArtistContribsByRef'],
-        transform: (coverArtFileExtension, {
-          albumData,
-          coverArtistContribsByRef,
-          hasCoverArt,
-          [Track.instance]: track,
-        }) =>
-          coverArtFileExtension ??
-          (Track.hasCoverArt(
-            track,
-            albumData,
-            coverArtistContribsByRef,
-            hasCoverArt
-          )
-            ? Track.findAlbum(track, albumData)?.trackCoverArtFileExtension
-            : Track.findAlbum(track, albumData)?.coverArtFileExtension) ??
-          'jpg',
-      },
-    },
-
-    originalReleaseTrackByRef: Thing.common.singleReference(Track),
-
-    dataSourceAlbumByRef: Thing.common.singleReference(Album),
-
-    commentary: Thing.common.commentary(),
-    lyrics: Thing.common.simpleString(),
-    additionalFiles: Thing.common.additionalFiles(),
-    sheetMusicFiles: Thing.common.additionalFiles(),
-    midiProjectFiles: Thing.common.additionalFiles(),
+    name: name('Unnamed Track'),
+    directory: directory(),
+
+    duration: duration(),
+    urls: urls(),
+    dateFirstReleased: simpleDate(),
+
+    color: [
+      exposeUpdateValueOrContinue({
+        validate: input.value(isColor),
+      }),
+
+      withContainingTrackSection(),
+
+      withPropertyFromObject({
+        object: '#trackSection',
+        property: input.value('color'),
+      }),
+
+      exposeDependencyOrContinue({dependency: '#trackSection.color'}),
+
+      withPropertyFromAlbum({
+        property: input.value('color'),
+      }),
+
+      exposeDependency({dependency: '#album.color'}),
+    ],
+
+    alwaysReferenceByDirectory: [
+      withAlwaysReferenceByDirectory(),
+      exposeDependency({dependency: '#alwaysReferenceByDirectory'}),
+    ],
+
+    // Disables presenting the track as though it has its own unique artwork.
+    // This flag should only be used in select circumstances, i.e. to override
+    // an album's trackCoverArtists. This flag supercedes that property, as well
+    // as the track's own coverArtists.
+    disableUniqueCoverArt: flag(),
+
+    // File extension for track's corresponding media file. This represents the
+    // track's unique cover artwork, if any, and does not inherit the extension
+    // of the album's main artwork. It does inherit trackCoverArtFileExtension,
+    // if present on the album.
+    coverArtFileExtension: [
+      exitWithoutUniqueCoverArt(),
+
+      exposeUpdateValueOrContinue({
+        validate: input.value(isFileExtension),
+      }),
+
+      withPropertyFromAlbum({
+        property: input.value('trackCoverArtFileExtension'),
+      }),
+
+      exposeDependencyOrContinue({dependency: '#album.trackCoverArtFileExtension'}),
+
+      exposeConstant({
+        value: input.value('jpg'),
+      }),
+    ],
+
+    // Date of cover art release. Like coverArtFileExtension, this represents
+    // only the track's own unique cover artwork, if any. This exposes only as
+    // the track's own coverArtDate or its album's trackArtDate, so if neither
+    // is specified, this value is null.
+    coverArtDate: [
+      withHasUniqueCoverArt(),
+
+      exitWithoutDependency({
+        dependency: '#hasUniqueCoverArt',
+        mode: input.value('falsy'),
+      }),
+
+      exposeUpdateValueOrContinue({
+        validate: input.value(isDate),
+      }),
+
+      withPropertyFromAlbum({
+        property: input.value('trackArtDate'),
+      }),
+
+      exposeDependency({dependency: '#album.trackArtDate'}),
+    ],
+
+    commentary: commentary(),
+    lyrics: simpleString(),
+
+    additionalFiles: additionalFiles(),
+    sheetMusicFiles: additionalFiles(),
+    midiProjectFiles: additionalFiles(),
+
+    originalReleaseTrack: singleReference({
+      class: input.value(Track),
+      find: input.value(find.track),
+      data: 'trackData',
+    }),
+
+    // Internal use only - for directly identifying an album inside a track's
+    // util.inspect display, if it isn't indirectly available (by way of being
+    // included in an album's track list).
+    dataSourceAlbum: singleReference({
+      class: input.value(Album),
+      find: input.value(find.album),
+      data: 'albumData',
+    }),
+
+    artistContribs: [
+      inheritFromOriginalRelease({
+        property: input.value('artistContribs'),
+      }),
+
+      withResolvedContribs({
+        from: input.updateValue({validate: isContributionList}),
+      }).outputs({
+        '#resolvedContribs': '#artistContribs',
+      }),
+
+      exposeDependencyOrContinue({
+        dependency: '#artistContribs',
+        mode: input.value('empty'),
+      }),
+
+      withPropertyFromAlbum({
+        property: input.value('artistContribs'),
+      }),
+
+      exposeDependency({dependency: '#album.artistContribs'}),
+    ],
+
+    contributorContribs: [
+      inheritFromOriginalRelease({
+        property: input.value('contributorContribs'),
+      }),
+
+      contributionList(),
+    ],
+
+    // Cover artists aren't inherited from the original release, since it
+    // typically varies by release and isn't defined by the musical qualities
+    // of the track.
+    coverArtistContribs: [
+      exitWithoutUniqueCoverArt({
+        value: input.value([]),
+      }),
+
+      withResolvedContribs({
+        from: input.updateValue({validate: isContributionList}),
+      }).outputs({
+        '#resolvedContribs': '#coverArtistContribs',
+      }),
+
+      exposeDependencyOrContinue({
+        dependency: '#coverArtistContribs',
+        mode: input.value('empty'),
+      }),
+
+      withPropertyFromAlbum({
+        property: input.value('trackCoverArtistContribs'),
+      }),
+
+      exposeDependency({dependency: '#album.trackCoverArtistContribs'}),
+    ],
+
+    referencedTracks: [
+      inheritFromOriginalRelease({
+        property: input.value('referencedTracks'),
+      }),
+
+      referenceList({
+        class: input.value(Track),
+        find: input.value(find.track),
+        data: 'trackData',
+      }),
+    ],
+
+    sampledTracks: [
+      inheritFromOriginalRelease({
+        property: input.value('sampledTracks'),
+      }),
+
+      referenceList({
+        class: input.value(Track),
+        find: input.value(find.track),
+        data: 'trackData',
+      }),
+    ],
+
+    artTags: referenceList({
+      class: input.value(ArtTag),
+      find: input.value(find.artTag),
+      data: 'artTagData',
+    }),
 
     // Update only
 
-    albumData: Thing.common.wikiData(Album),
-    artistData: Thing.common.wikiData(Artist),
-    artTagData: Thing.common.wikiData(ArtTag),
-    flashData: Thing.common.wikiData(Flash),
-    trackData: Thing.common.wikiData(Track),
+    albumData: wikiData(Album),
+    artistData: wikiData(Artist),
+    artTagData: wikiData(ArtTag),
+    flashData: wikiData(Flash),
+    trackData: wikiData(Track),
 
     // Expose only
 
-    commentatorArtists: Thing.common.commentatorArtists(),
-
-    album: {
-      flags: {expose: true},
-
-      expose: {
-        dependencies: ['albumData'],
-        compute: ({[Track.instance]: track, albumData}) =>
-          albumData?.find((album) => album.tracks.includes(track)) ?? null,
-      },
-    },
-
-    // Note - this is an internal property used only to help identify a track.
-    // It should not be assumed in general that the album and dataSourceAlbum match
-    // (i.e. a track may dynamically be moved from one album to another, at
-    // which point dataSourceAlbum refers to where it was originally from, and is
-    // not generally relevant information). It's also not guaranteed that
-    // dataSourceAlbum is available (depending on the Track creator to optionally
-    // provide dataSourceAlbumByRef).
-    dataSourceAlbum: Thing.common.dynamicThingFromSingleReference(
-      'dataSourceAlbumByRef',
-      'albumData',
-      find.album
-    ),
-
-    date: {
-      flags: {expose: true},
-
-      expose: {
-        dependencies: ['albumData', 'dateFirstReleased'],
-        compute: ({albumData, dateFirstReleased, [Track.instance]: track}) =>
-          dateFirstReleased ?? Track.findAlbum(track, albumData)?.date ?? null,
-      },
-    },
-
-    color: {
-      flags: {update: true, expose: true},
-
-      update: {validate: isColor},
-
-      expose: {
-        dependencies: ['albumData'],
-
-        transform: (color, {albumData, [Track.instance]: track}) =>
-          color ??
-            Track.findAlbum(track, albumData)
-              ?.trackSections.find(({tracks}) => tracks.includes(track))
-                ?.color ?? null,
-      },
-    },
-
-    coverArtDate: {
-      flags: {update: true, expose: true},
-
-      update: {validate: isDate},
-
-      expose: {
-        dependencies: [
-          'albumData',
-          'coverArtistContribsByRef',
-          'dateFirstReleased',
-          'hasCoverArt',
-        ],
-        transform: (coverArtDate, {
-          albumData,
-          coverArtistContribsByRef,
-          dateFirstReleased,
-          hasCoverArt,
-          [Track.instance]: track,
-        }) =>
-          (Track.hasCoverArt(track, albumData, coverArtistContribsByRef, hasCoverArt)
-            ? coverArtDate ??
-              dateFirstReleased ??
-              Track.findAlbum(track, albumData)?.trackArtDate ??
-              Track.findAlbum(track, albumData)?.date ??
-              null
-            : null),
-      },
-    },
-
-    hasUniqueCoverArt: {
-      flags: {expose: true},
-
-      expose: {
-        dependencies: ['albumData', 'coverArtistContribsByRef', 'hasCoverArt'],
-        compute: ({
-          albumData,
-          coverArtistContribsByRef,
-          hasCoverArt,
-          [Track.instance]: track,
-        }) =>
-          Track.hasUniqueCoverArt(
-            track,
-            albumData,
-            coverArtistContribsByRef,
-            hasCoverArt
-          ),
-      },
-    },
-
-    originalReleaseTrack: Thing.common.dynamicThingFromSingleReference(
-      'originalReleaseTrackByRef',
-      'trackData',
-      find.track
-    ),
-
-    otherReleases: {
-      flags: {expose: true},
-
-      expose: {
-        dependencies: ['originalReleaseTrackByRef', 'trackData'],
-
-        compute: ({
-          originalReleaseTrackByRef: t1origRef,
-          trackData,
-          [Track.instance]: t1,
-        }) => {
-          if (!trackData) {
-            return [];
-          }
-
-          const t1orig = find.track(t1origRef, trackData);
-
-          return [
-            t1orig,
-            ...trackData.filter((t2) => {
-              const {originalReleaseTrack: t2orig} = t2;
-              return t2 !== t1 && t2orig && (t2orig === t1orig || t2orig === t1);
-            }),
-          ].filter(Boolean);
-        },
-      },
-    },
-
-    artistContribs:
-      Track.inheritFromOriginalRelease('artistContribs', [],
-        Thing.common.dynamicInheritContribs(
-          null,
-          'artistContribsByRef',
-          'artistContribsByRef',
-          'albumData',
-          Track.findAlbum)),
-
-    contributorContribs:
-      Track.inheritFromOriginalRelease('contributorContribs', [],
-        Thing.common.dynamicContribs('contributorContribsByRef')),
-
-    // Cover artists aren't inherited from the original release, since it
-    // typically varies by release and isn't defined by the musical qualities
-    // of the track.
-    coverArtistContribs:
-      Thing.common.dynamicInheritContribs(
-        'hasCoverArt',
-        'coverArtistContribsByRef',
-        'trackCoverArtistContribsByRef',
-        'albumData',
-        Track.findAlbum),
-
-    referencedTracks:
-      Track.inheritFromOriginalRelease('referencedTracks', [],
-        Thing.common.dynamicThingsFromReferenceList(
-          'referencedTracksByRef',
-          'trackData',
-          find.track)),
-
-    sampledTracks:
-      Track.inheritFromOriginalRelease('sampledTracks', [],
-        Thing.common.dynamicThingsFromReferenceList(
-          'sampledTracksByRef',
-          'trackData',
-          find.track)),
-
-    // Specifically exclude re-releases from this list - while it's useful to
-    // get from a re-release to the tracks it references, re-releases aren't
-    // generally relevant from the perspective of the tracks being referenced.
-    // Filtering them from data here hides them from the corresponding field
-    // on the site (obviously), and has the bonus of not counting them when
-    // counting the number of times a track has been referenced, for use in
-    // the "Tracks - by Times Referenced" listing page (or other data
-    // processing).
-    referencedByTracks: {
-      flags: {expose: true},
-
-      expose: {
-        dependencies: ['trackData'],
-
-        compute: ({trackData, [Track.instance]: track}) =>
-          trackData
-            ? trackData
-                .filter((t) => !t.originalReleaseTrack)
-                .filter((t) => t.referencedTracks?.includes(track))
-            : [],
-      },
-    },
-
-    // For the same reasoning, exclude re-releases from sampled tracks too.
-    sampledByTracks: {
-      flags: {expose: true},
-
-      expose: {
-        dependencies: ['trackData'],
-
-        compute: ({trackData, [Track.instance]: track}) =>
-          trackData
-            ? trackData
-                .filter((t) => !t.originalReleaseTrack)
-                .filter((t) => t.sampledTracks?.includes(track))
-            : [],
-      },
-    },
-
-    featuredInFlashes: Thing.common.reverseReferenceList(
-      'flashData',
-      'featuredTracks'
-    ),
-
-    artTags: Thing.common.dynamicThingsFromReferenceList(
-      'artTagsByRef',
-      'artTagData',
-      find.artTag
-    ),
-  });
-
-  // This is a quick utility function for now, since the same code is reused in
-  // several places. Ideally it wouldn't be - we'd just reuse the `album`
-  // property - but support for that hasn't been coded yet :P
-  static findAlbum = (track, albumData) =>
-    albumData?.find((album) => album.tracks.includes(track));
-
-  // Another reused utility function. This one's logic is a bit more complicated.
-  static hasCoverArt(
-    track,
-    albumData,
-    coverArtistContribsByRef,
-    hasCoverArt
-  ) {
-    if (!empty(coverArtistContribsByRef)) {
-      return true;
-    }
+    commentatorArtists: commentatorArtists(),
 
-    const album = Track.findAlbum(track, albumData);
-    if (album && !empty(album.trackCoverArtistContribsByRef)) {
-      return true;
-    }
+    album: [
+      withAlbum(),
+      exposeDependency({dependency: '#album'}),
+    ],
 
-    return false;
-  }
+    date: [
+      exposeDependencyOrContinue({dependency: 'dateFirstReleased'}),
 
-  static hasUniqueCoverArt(
-    track,
-    albumData,
-    coverArtistContribsByRef,
-    hasCoverArt
-  ) {
-    if (!empty(coverArtistContribsByRef)) {
-      return true;
-    }
+      withPropertyFromAlbum({
+        property: input.value('date'),
+      }),
 
-    if (hasCoverArt === false) {
-      return false;
-    }
+      exposeDependency({dependency: '#album.date'}),
+    ],
 
-    const album = Track.findAlbum(track, albumData);
-    if (album && !empty(album.trackCoverArtistContribsByRef)) {
-      return true;
-    }
+    hasUniqueCoverArt: [
+      withHasUniqueCoverArt(),
+      exposeDependency({dependency: '#hasUniqueCoverArt'}),
+    ],
 
-    return false;
-  }
+    otherReleases: [
+      withOtherReleases(),
+      exposeDependency({dependency: '#otherReleases'}),
+    ],
 
-  static inheritFromOriginalRelease(
-    originalProperty,
-    originalMissingValue,
-    ownPropertyDescriptor
-  ) {
-    return {
-      flags: {expose: true},
-
-      expose: {
-        dependencies: [
-          ...ownPropertyDescriptor.expose.dependencies,
-          'originalReleaseTrackByRef',
-          'trackData',
-        ],
-
-        compute(dependencies) {
-          const {
-            originalReleaseTrackByRef,
-            trackData,
-          } = dependencies;
-
-          if (originalReleaseTrackByRef) {
-            if (!trackData) return originalMissingValue;
-            const original = find.track(originalReleaseTrackByRef, trackData, {mode: 'quiet'});
-            if (!original) return originalMissingValue;
-            return original[originalProperty];
-          }
-
-          return ownPropertyDescriptor.expose.compute(dependencies);
-        },
-      },
-    };
-  }
+    referencedByTracks: trackReverseReferenceList({
+      list: input.value('referencedTracks'),
+    }),
 
-  [inspect.custom]() {
-    const base = Thing.prototype[inspect.custom].apply(this);
+    sampledByTracks: trackReverseReferenceList({
+      list: input.value('sampledTracks'),
+    }),
 
-    const rereleasePart =
-      (this.originalReleaseTrackByRef
-        ? `${color.yellow('[rerelease]')} `
-        : ``);
+    featuredInFlashes: reverseReferenceList({
+      data: 'flashData',
+      list: input.value('featuredTracks'),
+    }),
+  });
 
-    const {album, dataSourceAlbum} = this;
+  [inspect.custom](depth) {
+    const parts = [];
 
-    const albumName =
-      (album
-        ? album.name
-        : dataSourceAlbum?.name);
+    parts.push(Thing.prototype[inspect.custom].apply(this));
 
-    const albumIndex =
-      albumName &&
-        (album
-          ? album.tracks.indexOf(this)
-          : dataSourceAlbum.tracks.indexOf(this));
+    if (CacheableObject.getUpdateValue(this, 'originalReleaseTrack')) {
+      parts.unshift(`${colors.yellow('[rerelease]')} `);
+    }
 
-    const trackNum =
-      albumName &&
+    let album;
+    if (depth >= 0 && (album = this.album ?? this.dataSourceAlbum)) {
+      const albumName = album.name;
+      const albumIndex = album.tracks.indexOf(this);
+      const trackNum =
         (albumIndex === -1
           ? '#?'
           : `#${albumIndex + 1}`);
+      parts.push(` (${colors.yellow(trackNum)} in ${colors.green(albumName)})`);
+    }
 
-    const albumPart =
-      albumName
-        ? ` (${color.yellow(trackNum)} in ${color.green(albumName)})`
-        : ``;
-
-    return rereleasePart + base + albumPart;
+    return parts.join('');
   }
 }
diff --git a/src/data/things/validators.js b/src/data/things/validators.js
index fc953c2a..ee301f15 100644
--- a/src/data/things/validators.js
+++ b/src/data/things/validators.js
@@ -1,7 +1,7 @@
 import {inspect as nodeInspect} from 'node:util';
 
-import {color, ENABLE_COLOR} from '#cli';
-import {withAggregate} from '#sugar';
+import {colors, ENABLE_COLOR} from '#cli';
+import {empty, typeAppearance, withAggregate} from '#sugar';
 
 function inspect(value) {
   return nodeInspect(value, {colors: ENABLE_COLOR});
@@ -9,13 +9,13 @@ function inspect(value) {
 
 // Basic types (primitives)
 
-function a(noun) {
+export function a(noun) {
   return /[aeiou]/.test(noun[0]) ? `an ${noun}` : `a ${noun}`;
 }
 
-function isType(value, type) {
+export function isType(value, type) {
   if (typeof value !== type)
-    throw new TypeError(`Expected ${a(type)}, got ${typeof value}`);
+    throw new TypeError(`Expected ${a(type)}, got ${typeAppearance(value)}`);
 
   return true;
 }
@@ -132,7 +132,7 @@ export function isObject(value) {
 
 export function isArray(value) {
   if (typeof value !== 'object' || value === null || !Array.isArray(value))
-    throw new TypeError(`Expected an array, got ${value}`);
+    throw new TypeError(`Expected an array, got ${typeAppearance(value)}`);
 
   return true;
 }
@@ -174,7 +174,8 @@ function validateArrayItemsHelper(itemValidator) {
         throw new Error(`Expected validator to return true`);
       }
     } catch (error) {
-      error.message = `(index: ${color.green(index)}, item: ${inspect(item)}) ${error.message}`;
+      error.message = `(index: ${colors.yellow(`${index}`)}, item: ${inspect(item)}) ${error.message}`;
+      error[Symbol.for('hsmusic.decorate.indexInSourceArray')] = index;
       throw error;
     }
   };
@@ -264,7 +265,7 @@ export function validateProperties(spec) {
           try {
             specValidator(value);
           } catch (error) {
-            error.message = `(key: ${color.green(specKey)}, value: ${inspect(value)}) ${error.message}`;
+            error.message = `(key: ${colors.green(specKey)}, value: ${inspect(value)}) ${error.message}`;
             throw error;
           }
         });
@@ -308,7 +309,7 @@ export const isTrackSection = validateProperties({
   color: optional(isColor),
   dateOriginallyReleased: optional(isDate),
   isDefaultTrackSection: optional(isBoolean),
-  tracksByRef: optional(validateReferenceList('track')),
+  tracks: optional(validateReferenceList('track')),
 });
 
 export const isTrackSectionList = validateArrayItems(isTrackSection);
@@ -404,6 +405,76 @@ export function validateReferenceList(type = '') {
   return validateArrayItems(validateReference(type));
 }
 
+const validateWikiData_cache = {};
+
+export function validateWikiData({
+  referenceType = '',
+  allowMixedTypes = false,
+}) {
+  if (referenceType && allowMixedTypes) {
+    throw new TypeError(`Don't specify both referenceType and allowMixedTypes`);
+  }
+
+  validateWikiData_cache[referenceType] ??= {};
+  validateWikiData_cache[referenceType][allowMixedTypes] ??= new WeakMap();
+
+  const isArrayOfObjects = validateArrayItems(isObject);
+
+  return (array) => {
+    const subcache = validateWikiData_cache[referenceType][allowMixedTypes];
+    if (subcache.has(array)) return subcache.get(array);
+
+    let OK = false;
+
+    try {
+      isArrayOfObjects(array);
+
+      if (empty(array)) {
+        OK = true; return true;
+      }
+
+      const allRefTypes =
+        new Set(array.map(object =>
+          object.constructor[Symbol.for('Thing.referenceType')]));
+
+      if (allRefTypes.has(undefined)) {
+        if (allRefTypes.size === 1) {
+          throw new TypeError(`Expected array of wiki data objects, got array of other objects`);
+        } else {
+          throw new TypeError(`Expected array of wiki data objects, got mixed items`);
+        }
+      }
+
+      if (allRefTypes.size > 1) {
+        if (allowMixedTypes) {
+          OK = true; return true;
+        }
+
+        const types = () => Array.from(allRefTypes).join(', ');
+
+        if (referenceType) {
+          if (allRefTypes.has(referenceType)) {
+            allRefTypes.remove(referenceType);
+            throw new TypeError(`Expected array of only ${referenceType}, also got other types: ${types()}`)
+          } else {
+            throw new TypeError(`Expected array of only ${referenceType}, got other types: ${types()}`);
+          }
+        }
+
+        throw new TypeError(`Expected array of unmixed reference types, got multiple: ${types()}`);
+      }
+
+      if (referenceType && !allRefTypes.has(referenceType)) {
+        throw new TypeError(`Expected array of ${referenceType}, got array of ${allRefTypes[0]}`)
+      }
+
+      OK = true; return true;
+    } finally {
+      subcache.set(array, OK);
+    }
+  };
+}
+
 // Compositional utilities
 
 export function oneOf(...checks) {
diff --git a/src/data/things/wiki-info.js b/src/data/things/wiki-info.js
index e906cab1..6286a267 100644
--- a/src/data/things/wiki-info.js
+++ b/src/data/things/wiki-info.js
@@ -1,20 +1,25 @@
+import {input} from '#composite';
 import find from '#find';
+import {isLanguageCode, isName, isURL} from '#validators';
+
+import {
+  color,
+  flag,
+  name,
+  referenceList,
+  simpleString,
+  wikiData,
+} from '#composite/wiki-properties';
 
 import Thing from './thing.js';
 
 export class WikiInfo extends Thing {
-  static [Thing.getPropertyDescriptors] = ({
-    Group,
+  static [Thing.friendlyName] = `Wiki Info`;
 
-    validators: {
-      isLanguageCode,
-      isName,
-      isURL,
-    },
-  }) => ({
+  static [Thing.getPropertyDescriptors] = ({Group}) => ({
     // Update & expose
 
-    name: Thing.common.name('Unnamed Wiki'),
+    name: name('Unnamed Wiki'),
 
     // Displayed in nav bar.
     nameShort: {
@@ -27,12 +32,12 @@ export class WikiInfo extends Thing {
       },
     },
 
-    color: Thing.common.color(),
+    color: color(),
 
     // One-line description used for <meta rel="description"> tag.
-    description: Thing.common.simpleString(),
+    description: simpleString(),
 
-    footerContent: Thing.common.simpleString(),
+    footerContent: simpleString(),
 
     defaultLanguage: {
       flags: {update: true, expose: true},
@@ -44,25 +49,21 @@ export class WikiInfo extends Thing {
       update: {validate: isURL},
     },
 
-    divideTrackListsByGroupsByRef: Thing.common.referenceList(Group),
+    divideTrackListsByGroups: referenceList({
+      class: input.value(Group),
+      find: input.value(find.group),
+      data: 'groupData',
+    }),
 
     // Feature toggles
-    enableFlashesAndGames: Thing.common.flag(false),
-    enableListings: Thing.common.flag(false),
-    enableNews: Thing.common.flag(false),
-    enableArtTagUI: Thing.common.flag(false),
-    enableGroupUI: Thing.common.flag(false),
+    enableFlashesAndGames: flag(false),
+    enableListings: flag(false),
+    enableNews: flag(false),
+    enableArtTagUI: flag(false),
+    enableGroupUI: flag(false),
 
     // Update only
 
-    groupData: Thing.common.wikiData(Group),
-
-    // Expose only
-
-    divideTrackListsByGroups: Thing.common.dynamicThingsFromReferenceList(
-      'divideTrackListsByGroupsByRef',
-      'groupData',
-      find.group
-    ),
+    groupData: wikiData(Group),
   });
 }
diff --git a/src/data/yaml.js b/src/data/yaml.js
index 35943199..f7856cb7 100644
--- a/src/data/yaml.js
+++ b/src/data/yaml.js
@@ -7,10 +7,15 @@ import {inspect as nodeInspect} from 'node:util';
 
 import yaml from 'js-yaml';
 
-import {color, ENABLE_COLOR, logInfo, logWarn} from '#cli';
+import {colors, ENABLE_COLOR, logInfo, logWarn} from '#cli';
 import find, {bindFind} from '#find';
 import {traverse} from '#node-utils';
-import T from '#things';
+
+import T, {
+  CacheableObject,
+  CacheableObjectPropertyValueError,
+  Thing,
+} from '#things';
 
 import {
   conditionallySuppressError,
@@ -59,7 +64,7 @@ export const DATA_STATIC_PAGE_DIRECTORY = 'static-page';
 // document and apply the configuration passed to makeProcessDocument in order
 // to construct a Thing subclass.
 function makeProcessDocument(
-  thingClass,
+  thingConstructor,
   {
     // Optional early step for transforming field values before providing them
     // to the Thing's update() method. This is useful when the input format
@@ -110,7 +115,7 @@ function makeProcessDocument(
     invalidFieldCombinations = [],
   }
 ) {
-  if (!thingClass) {
+  if (!thingConstructor) {
     throw new Error(`Missing Thing class`);
   }
 
@@ -137,22 +142,47 @@ function makeProcessDocument(
         const name = document[nameField];
         error.message = name
           ? `(name: ${inspect(name)}) ${error.message}`
-          : `(${color.dim(`no name found`)}) ${error.message}`;
+          : `(${colors.dim(`no name found`)}) ${error.message}`;
         throw error;
       }
     };
   };
 
   const fn = decorateErrorWithName((document) => {
+    const nameField = propertyFieldMapping['name'];
+    const namePart =
+      (nameField
+        ? (document[nameField]
+          ? ` named ${colors.green(`"${document[nameField]}"`)}`
+          : ` (name field, "${nameField}", not specified)`)
+        : ``);
+
+    const constructorPart =
+      (thingConstructor[Thing.friendlyName]
+        ? colors.green(thingConstructor[Thing.friendlyName])
+     : thingConstructor.name
+        ? colors.green(thingConstructor.name)
+        : `document`);
+
+    const aggregate = openAggregate({
+      message: `Errors processing ${constructorPart}` + namePart,
+    });
+
     const documentEntries = Object.entries(document)
       .filter(([field]) => !ignoredFields.includes(field));
 
+    const skippedFields = new Set();
+
     const unknownFields = documentEntries
       .map(([field]) => field)
       .filter((field) => !knownFields.includes(field));
 
     if (!empty(unknownFields)) {
-      throw new makeProcessDocument.UnknownFieldsError(unknownFields);
+      aggregate.push(new UnknownFieldsError(unknownFields));
+
+      for (const field of unknownFields) {
+        skippedFields.add(field);
+      }
     }
 
     const presentFields = Object.keys(document);
@@ -162,28 +192,57 @@ function makeProcessDocument(
     for (const {message, fields} of invalidFieldCombinations) {
       const fieldsPresent = presentFields.filter(field => fields.includes(field));
 
-      if (fieldsPresent.length <= 1) {
-        continue;
-      }
+      if (fieldsPresent.length >= 2) {
+        const filteredDocument =
+          filterProperties(
+            document,
+            fieldsPresent,
+            {preserveOriginalOrder: true});
 
-      fieldCombinationErrors.push(
-        new makeProcessDocument.FieldCombinationError(
-          filterProperties(document, fieldsPresent),
-          message));
+        fieldCombinationErrors.push(new FieldCombinationError(filteredDocument, message));
+
+        for (const field of Object.keys(filteredDocument)) {
+          skippedFields.add(field);
+        }
+      }
     }
 
     if (!empty(fieldCombinationErrors)) {
-      throw new makeProcessDocument.FieldCombinationsError(fieldCombinationErrors);
+      aggregate.push(new FieldCombinationAggregateError(fieldCombinationErrors));
     }
 
     const fieldValues = {};
 
-    for (const [field, value] of documentEntries) {
-      if (Object.hasOwn(fieldTransformations, field)) {
-        fieldValues[field] = fieldTransformations[field](value);
-      } else {
-        fieldValues[field] = value;
+    for (const [field, documentValue] of documentEntries) {
+      if (skippedFields.has(field)) continue;
+
+      // This variable would like to certify itself as "not into capitalism".
+      let propertyValue =
+        (Object.hasOwn(fieldTransformations, field)
+          ? fieldTransformations[field](documentValue)
+          : documentValue);
+
+      // Completely blank items in a YAML list are read as null.
+      // They're handy to have around when filling out a document and shouldn't
+      // be considered an error (or data at all).
+      if (Array.isArray(propertyValue)) {
+        const wasEmpty = empty(propertyValue);
+
+        propertyValue =
+          propertyValue.filter(item => item !== null);
+
+        const isEmpty = empty(propertyValue);
+
+        // Don't set arrays which are empty as a result of the above filter.
+        // Arrays which were originally empty, i.e. `Field: []`, are still
+        // valid data, but if it's just an array not containing any filled out
+        // items, it should be treated as a placeholder and skipped over.
+        if (isEmpty && !wasEmpty) {
+          propertyValue = null;
+        }
       }
+
+      fieldValues[field] = propertyValue;
     }
 
     const sourceProperties = {};
@@ -193,15 +252,34 @@ function makeProcessDocument(
       sourceProperties[property] = value;
     }
 
-    const thing = Reflect.construct(thingClass, []);
+    const thing = Reflect.construct(thingConstructor, []);
 
-    withAggregate({message: `Errors applying ${color.green(thingClass.name)} properties`}, ({call}) => {
-      for (const [property, value] of Object.entries(sourceProperties)) {
-        call(() => (thing[property] = value));
+    const fieldValueErrors = [];
+
+    for (const [property, value] of Object.entries(sourceProperties)) {
+      const field = propertyFieldMapping[property];
+      try {
+        thing[property] = value;
+      } catch (caughtError) {
+        skippedFields.add(field);
+        fieldValueErrors.push(new FieldValueError(field, property, value, caughtError));
       }
-    });
+    }
+
+    if (!empty(fieldValueErrors)) {
+      aggregate.push(new FieldValueAggregateError(thingConstructor, fieldValueErrors));
+    }
 
-    return thing;
+    if (skippedFields.size >= 1) {
+      aggregate.push(
+        new SkippedFieldsSummaryError(
+          filterProperties(
+            document,
+            Array.from(skippedFields),
+            {preserveOriginalOrder: true})));
+    }
+
+    return {thing, aggregate};
   });
 
   Object.assign(fn, {
@@ -212,36 +290,81 @@ function makeProcessDocument(
   return fn;
 }
 
-makeProcessDocument.UnknownFieldsError = class UnknownFieldsError extends Error {
+export class UnknownFieldsError extends Error {
   constructor(fields) {
-    super(`Unknown fields present: ${fields.join(', ')}`);
+    super(`Unknown fields ignored: ${fields.map(field => colors.red(field)).join(', ')}`);
     this.fields = fields;
   }
-};
+}
 
-makeProcessDocument.FieldCombinationsError = class FieldCombinationsError extends AggregateError {
+export class FieldCombinationAggregateError extends AggregateError {
   constructor(errors) {
-    super(errors, `Errors in combinations of fields present`);
+    super(errors, `Invalid field combinations - all involved fields ignored`);
   }
-};
+}
 
-makeProcessDocument.FieldCombinationError = class FieldCombinationError extends Error {
+export class FieldCombinationError extends Error {
   constructor(fields, message) {
     const fieldNames = Object.keys(fields);
-    const combinePart = `Don't combine ${fieldNames.map(field => color.red(field)).join(', ')}`;
 
-    const messagePart =
+    const mainMessage = `Don't combine ${fieldNames.map(field => colors.red(field)).join(', ')}`;
+
+    const causeMessage =
       (typeof message === 'function'
-        ? `: ${message(fields)}`
+        ? message(fields)
      : typeof message === 'string'
-        ? `: ${message}`
-        : ``);
+        ? message
+        : null);
+
+    super(mainMessage, {
+      cause:
+        (causeMessage
+          ? new Error(causeMessage)
+          : null),
+    });
 
-    super(combinePart + messagePart);
     this.fields = fields;
   }
 }
 
+export class FieldValueAggregateError extends AggregateError {
+  constructor(thingConstructor, errors) {
+    super(errors, `Errors processing field values for ${colors.green(thingConstructor.name)}`);
+  }
+}
+
+export class FieldValueError extends Error {
+  constructor(field, property, value, caughtError) {
+    const cause =
+      (caughtError instanceof CacheableObjectPropertyValueError
+        ? caughtError.cause
+        : caughtError);
+
+    super(
+      `Failed to set ${colors.green(`"${field}"`)} field (${colors.green(property)}) to ${inspect(value)}`,
+      {cause});
+  }
+}
+
+export class SkippedFieldsSummaryError extends Error {
+  constructor(filteredDocument) {
+    const entries = Object.entries(filteredDocument);
+
+    const lines =
+      entries.map(([field, value]) =>
+        ` - ${field}: ` +
+        inspect(value)
+          .split('\n')
+          .map((line, index) => index === 0 ? line : `   ${line}`)
+          .join('\n'));
+
+    super(
+      colors.bright(colors.yellow(`Altogether, skipped ${entries.length === 1 ? `1 field` : `${entries.length} fields`}:\n`)) +
+      lines.join('\n') + '\n' +
+      colors.bright(colors.yellow(`See above errors for details.`)));
+  }
+}
+
 export const processAlbumDocument = makeProcessDocument(T.Album, {
   fieldTransformations: {
     'Artists': parseContributors,
@@ -278,11 +401,11 @@ export const processAlbumDocument = makeProcessDocument(T.Album, {
     coverArtFileExtension: 'Cover Art File Extension',
     trackCoverArtFileExtension: 'Track Art File Extension',
 
-    wallpaperArtistContribsByRef: 'Wallpaper Artists',
+    wallpaperArtistContribs: 'Wallpaper Artists',
     wallpaperStyle: 'Wallpaper Style',
     wallpaperFileExtension: 'Wallpaper File Extension',
 
-    bannerArtistContribsByRef: 'Banner Artists',
+    bannerArtistContribs: 'Banner Artists',
     bannerStyle: 'Banner Style',
     bannerFileExtension: 'Banner File Extension',
     bannerDimensions: 'Banner Dimensions',
@@ -290,11 +413,11 @@ export const processAlbumDocument = makeProcessDocument(T.Album, {
     commentary: 'Commentary',
     additionalFiles: 'Additional Files',
 
-    artistContribsByRef: 'Artists',
-    coverArtistContribsByRef: 'Cover Artists',
-    trackCoverArtistContribsByRef: 'Default Track Cover Artists',
-    groupsByRef: 'Groups',
-    artTagsByRef: 'Art Tags',
+    artistContribs: 'Artists',
+    coverArtistContribs: 'Cover Artists',
+    trackCoverArtistContribs: 'Default Track Cover Artists',
+    groups: 'Groups',
+    artTags: 'Art Tags',
   },
 });
 
@@ -316,6 +439,10 @@ export const processTrackDocument = makeProcessDocument(T.Track, {
 
     'Date First Released': (value) => new Date(value),
     'Cover Art Date': (value) => new Date(value),
+    'Has Cover Art': (value) =>
+      (value === true ? false :
+       value === false ? true :
+       value),
 
     'Artists': parseContributors,
     'Contributors': parseContributors,
@@ -336,7 +463,9 @@ export const processTrackDocument = makeProcessDocument(T.Track, {
     dateFirstReleased: 'Date First Released',
     coverArtDate: 'Cover Art Date',
     coverArtFileExtension: 'Cover Art File Extension',
-    hasCoverArt: 'Has Cover Art',
+    disableUniqueCoverArt: 'Has Cover Art', // This gets transformed to flip true/false.
+
+    alwaysReferenceByDirectory: 'Always Reference By Directory',
 
     lyrics: 'Lyrics',
     commentary: 'Commentary',
@@ -344,13 +473,13 @@ export const processTrackDocument = makeProcessDocument(T.Track, {
     sheetMusicFiles: 'Sheet Music Files',
     midiProjectFiles: 'MIDI Project Files',
 
-    originalReleaseTrackByRef: 'Originally Released As',
-    referencedTracksByRef: 'Referenced Tracks',
-    sampledTracksByRef: 'Sampled Tracks',
-    artistContribsByRef: 'Artists',
-    contributorContribsByRef: 'Contributors',
-    coverArtistContribsByRef: 'Cover Artists',
-    artTagsByRef: 'Art Tags',
+    originalReleaseTrack: 'Originally Released As',
+    referencedTracks: 'Referenced Tracks',
+    sampledTracks: 'Sampled Tracks',
+    artistContribs: 'Artists',
+    contributorContribs: 'Contributors',
+    coverArtistContribs: 'Cover Artists',
+    artTags: 'Art Tags',
   },
 
   invalidFieldCombinations: [
@@ -415,21 +544,25 @@ export const processFlashDocument = makeProcessDocument(T.Flash, {
     name: 'Flash',
     directory: 'Directory',
     page: 'Page',
+    color: 'Color',
     urls: 'URLs',
 
     date: 'Date',
     coverArtFileExtension: 'Cover Art File Extension',
 
-    featuredTracksByRef: 'Featured Tracks',
-    contributorContribsByRef: 'Contributors',
+    featuredTracks: 'Featured Tracks',
+    contributorContribs: 'Contributors',
   },
 });
 
 export const processFlashActDocument = makeProcessDocument(T.FlashAct, {
   propertyFieldMapping: {
     name: 'Act',
+    directory: 'Directory',
+
     color: 'Color',
-    anchor: 'Anchor',
+    listTerminology: 'List Terminology',
+
     jump: 'Jump',
     jumpColor: 'Jump Color',
   },
@@ -466,7 +599,7 @@ export const processGroupDocument = makeProcessDocument(T.Group, {
     description: 'Description',
     urls: 'URLs',
 
-    featuredAlbumsByRef: 'Featured Albums',
+    featuredAlbums: 'Featured Albums',
   },
 });
 
@@ -497,7 +630,7 @@ export const processWikiInfoDocument = makeProcessDocument(T.WikiInfo, {
     footerContent: 'Footer Content',
     defaultLanguage: 'Default Language',
     canonicalBase: 'Canonical Base',
-    divideTrackListsByGroupsByRef: 'Divide Track Lists By Groups',
+    divideTrackListsByGroups: 'Divide Track Lists By Groups',
     enableFlashesAndGames: 'Enable Flashes & Games',
     enableListings: 'Enable Listings',
     enableNews: 'Enable News',
@@ -532,9 +665,9 @@ export const homepageLayoutRowTypeProcessMapping = {
   albums: makeProcessHomepageLayoutRowDocument(T.HomepageLayoutAlbumsRow, {
     propertyFieldMapping: {
       displayStyle: 'Display Style',
-      sourceGroupByRef: 'Group',
+      sourceGroup: 'Group',
       countAlbumsFromGroup: 'Count',
-      sourceAlbumsByRef: 'Albums',
+      sourceAlbums: 'Albums',
       actionLinks: 'Actions',
     },
   }),
@@ -591,33 +724,17 @@ export function parseContributors(contributors) {
     return contributors;
   }
 
-  if (contributors.length === 1 && contributors[0].startsWith('<i>')) {
-    const arr = [];
-    arr.textContent = contributors[0];
-    return arr;
-  }
-
   contributors = contributors.map((contrib) => {
-    // 8asically, the format is "Who (What)", or just "Who". 8e sure to
-    // keep in mind that "what" doesn't necessarily have a value!
+    if (typeof contrib !== 'string') return contrib;
+
     const match = contrib.match(/^(.*?)( \((.*)\))?$/);
-    if (!match) {
-      return contrib;
-    }
+    if (!match) return contrib;
+
     const who = match[1];
     const what = match[3] || null;
     return {who, what};
   });
 
-  const badContributor = contributors.find((val) => typeof val === 'string');
-  if (badContributor) {
-    throw new Error(`Incorrectly formatted contribution: "${badContributor}".`);
-  }
-
-  if (contributors.length === 1 && contributors[0].who === 'none') {
-    return null;
-  }
-
   return contributors;
 }
 
@@ -767,13 +884,13 @@ export const dataSteps = [
         let currentTrackSection = {
           name: `Default Track Section`,
           isDefaultTrackSection: true,
-          tracksByRef: [],
+          tracks: [],
         };
 
-        const albumRef = T.Thing.getReference(album);
+        const albumRef = Thing.getReference(album);
 
         const closeCurrentTrackSection = () => {
-          if (!empty(currentTrackSection.tracksByRef)) {
+          if (!empty(currentTrackSection.tracks)) {
             trackSections.push(currentTrackSection);
           }
         };
@@ -787,7 +904,7 @@ export const dataSteps = [
               color: entry.color,
               dateOriginallyReleased: entry.dateOriginallyReleased,
               isDefaultTrackSection: false,
-              tracksByRef: [],
+              tracks: [],
             };
 
             continue;
@@ -795,9 +912,9 @@ export const dataSteps = [
 
           trackData.push(entry);
 
-          entry.dataSourceAlbumByRef = albumRef;
+          entry.dataSourceAlbum = albumRef;
 
-          currentTrackSection.tracksByRef.push(T.Thing.getReference(entry));
+          currentTrackSection.tracks.push(Thing.getReference(entry));
         }
 
         closeCurrentTrackSection();
@@ -821,12 +938,12 @@ export const dataSteps = [
       const artistData = results;
 
       const artistAliasData = results.flatMap((artist) => {
-        const origRef = T.Thing.getReference(artist);
+        const origRef = Thing.getReference(artist);
         return artist.aliasNames?.map((name) => {
           const alias = new T.Artist();
           alias.name = name;
           alias.isAlias = true;
-          alias.aliasedArtistRef = origRef;
+          alias.aliasedArtist = origRef;
           alias.artistData = artistData;
           return alias;
         }) ?? [];
@@ -850,7 +967,7 @@ export const dataSteps = [
 
     save(results) {
       let flashAct;
-      let flashesByRef = [];
+      let flashRefs = [];
 
       if (results[0] && !(results[0] instanceof T.FlashAct)) {
         throw new Error(`Expected an act at top of flash data file`);
@@ -859,18 +976,18 @@ export const dataSteps = [
       for (const thing of results) {
         if (thing instanceof T.FlashAct) {
           if (flashAct) {
-            Object.assign(flashAct, {flashesByRef});
+            Object.assign(flashAct, {flashes: flashRefs});
           }
 
           flashAct = thing;
-          flashesByRef = [];
+          flashRefs = [];
         } else {
-          flashesByRef.push(T.Thing.getReference(thing));
+          flashRefs.push(Thing.getReference(thing));
         }
       }
 
       if (flashAct) {
-        Object.assign(flashAct, {flashesByRef});
+        Object.assign(flashAct, {flashes: flashRefs});
       }
 
       const flashData = results.filter((x) => x instanceof T.Flash);
@@ -893,7 +1010,7 @@ export const dataSteps = [
 
     save(results) {
       let groupCategory;
-      let groupsByRef = [];
+      let groupRefs = [];
 
       if (results[0] && !(results[0] instanceof T.GroupCategory)) {
         throw new Error(`Expected a category at top of group data file`);
@@ -902,18 +1019,18 @@ export const dataSteps = [
       for (const thing of results) {
         if (thing instanceof T.GroupCategory) {
           if (groupCategory) {
-            Object.assign(groupCategory, {groupsByRef});
+            Object.assign(groupCategory, {groups: groupRefs});
           }
 
           groupCategory = thing;
-          groupsByRef = [];
+          groupRefs = [];
         } else {
-          groupsByRef.push(T.Thing.getReference(thing));
+          groupRefs.push(Thing.getReference(thing));
         }
       }
 
       if (groupCategory) {
-        Object.assign(groupCategory, {groupsByRef});
+        Object.assign(groupCategory, {groups: groupRefs});
       }
 
       const groupData = results.filter((x) => x instanceof T.Group);
@@ -925,6 +1042,10 @@ export const dataSteps = [
 
   {
     title: `Process homepage layout file`,
+
+    // Kludge: This benefits from the same headerAndEntries style messaging as
+    // albums and tracks (for example), but that document mode is designed to
+    // support multiple files, and only one is actually getting processed here.
     files: [HOMEPAGE_LAYOUT_DATA_FILE],
 
     documentMode: documentModes.headerAndEntries,
@@ -1005,7 +1126,7 @@ export async function loadAndProcessDataDocuments({dataPath}) {
       } catch (error) {
         error.message +=
           (error.message.includes('\n') ? '\n' : ' ') +
-          `(file: ${color.bright(color.blue(path.relative(dataPath, x.file)))})`;
+          `(file: ${colors.bright(colors.blue(path.relative(dataPath, x.file)))})`;
         throw error;
       }
     };
@@ -1013,8 +1134,8 @@ export async function loadAndProcessDataDocuments({dataPath}) {
 
   for (const dataStep of dataSteps) {
     await processDataAggregate.nestAsync(
-      {message: `Errors during data step: ${dataStep.title}`},
-      async ({call, callAsync, map, mapAsync, nest}) => {
+      {message: `Errors during data step: ${colors.bright(dataStep.title)}`},
+      async ({call, callAsync, map, mapAsync, push, nest}) => {
         const {documentMode} = dataStep;
 
         if (!Object.values(documentModes).includes(documentMode)) {
@@ -1028,7 +1149,7 @@ export async function loadAndProcessDataDocuments({dataPath}) {
         // just without the callbacks. Thank you.
         const filterBlankDocuments = documents => {
           const aggregate = openAggregate({
-            message: `Found blank documents - check for extra '${color.cyan(`---`)}'`,
+            message: `Found blank documents - check for extra '${colors.cyan(`---`)}'`,
           });
 
           const filteredDocuments =
@@ -1072,10 +1193,10 @@ export async function loadAndProcessDataDocuments({dataPath}) {
 
               if (count === 1) {
                 const range = `#${start + 1}`;
-                parts.push(`${count} document (${color.yellow(range)}), `);
+                parts.push(`${count} document (${colors.yellow(range)}), `);
               } else {
                 const range = `#${start + 1}-${end + 1}`;
-                parts.push(`${count} documents (${color.yellow(range)}), `);
+                parts.push(`${count} documents (${colors.yellow(range)}), `);
               }
 
               if (previous === null) {
@@ -1085,7 +1206,7 @@ export async function loadAndProcessDataDocuments({dataPath}) {
               } else {
                 const previousDescription = Object.entries(previous).at(0).join(': ');
                 const nextDescription = Object.entries(next).at(0).join(': ');
-                parts.push(`between "${color.cyan(previousDescription)}" and "${color.cyan(nextDescription)}"`);
+                parts.push(`between "${colors.cyan(previousDescription)}" and "${colors.cyan(nextDescription)}"`);
               }
 
               aggregate.push(new Error(parts.join('')));
@@ -1139,32 +1260,52 @@ export async function loadAndProcessDataDocuments({dataPath}) {
             return;
           }
 
-          const yamlResult =
-            documentMode === documentModes.oneDocumentTotal
-              ? call(yaml.load, readResult)
-              : call(yaml.loadAll, readResult);
+          let processResults;
 
-          if (!yamlResult) {
-            return;
-          }
+          switch (documentMode) {
+            case documentModes.oneDocumentTotal: {
+              const yamlResult = call(yaml.load, readResult);
 
-          let processResults;
+              if (!yamlResult) {
+                processResults = null;
+                break;
+              }
+
+              const {thing, aggregate} =
+                dataStep.processDocument(yamlResult);
+
+              processResults = thing;
+
+              call(() => aggregate.close());
+
+              break;
+            }
+
+            case documentModes.allInOne: {
+              const yamlResults = call(yaml.loadAll, readResult);
+
+              if (!yamlResults) {
+                processResults = [];
+                return;
+              }
+
+              const {documents, aggregate: filterAggregate} =
+                filterBlankDocuments(yamlResults);
+
+              call(filterAggregate.close);
+
+              processResults = [];
 
-          if (documentMode === documentModes.oneDocumentTotal) {
-            nest({message: `Errors processing document`}, ({call}) => {
-              processResults = call(dataStep.processDocument, yamlResult);
-            });
-          } else {
-            const {documents, aggregate: aggregate1} = filterBlankDocuments(yamlResult);
-            call(aggregate1.close);
-
-            const {result, aggregate: aggregate2} = mapAggregate(
-              documents,
-              decorateErrorWithIndex(dataStep.processDocument),
-              {message: `Errors processing documents`});
-            call(aggregate2.close);
-
-            processResults = result;
+              map(documents, decorateErrorWithIndex(document => {
+                const {thing, aggregate} =
+                  dataStep.processDocument(document);
+
+                processResults.push(thing);
+                aggregate.close();
+              }), {message: `Errors processing documents`});
+
+              break;
+            }
           }
 
           if (!processResults) return;
@@ -1222,81 +1363,74 @@ export async function loadAndProcessDataDocuments({dataPath}) {
           return {file, documents: filteredDocuments};
         });
 
-        let processResults;
+        const processResults = [];
 
-        if (documentMode === documentModes.headerAndEntries) {
-          nest({message: `Errors processing data files as valid documents`}, ({call, map}) => {
-            processResults = [];
+        switch (documentMode) {
+          case documentModes.headerAndEntries:
+            map(yamlResults, decorateErrorWithFile(({documents}) => {
+              const headerDocument = documents[0];
+              const entryDocuments = documents.slice(1).filter(Boolean);
 
-            yamlResults.forEach(({file, documents}) => {
-              const [headerDocument, ...entryDocuments] = documents;
+              if (!headerDocument)
+                throw new Error(`Missing header document (empty file or erroneously starting with "---"?)`);
 
-              if (!headerDocument) {
-                call(decorateErrorWithFile(() => {
-                  throw new Error(`Missing header document (empty file or erroneously starting with "---"?)`);
-                }), {file});
-                return;
-              }
+              // This'll be decorated with the file, and groups together any
+              // errors from processing the header and entry documents.
+              const fileAggregate =
+                openAggregate({message: `Errors processing documents`});
 
-              const header = call(
-                decorateErrorWithFile(({document}) =>
-                  dataStep.processHeaderDocument(document)),
-                {file, document: headerDocument});
+              const {thing: headerObject, aggregate: headerAggregate} =
+                dataStep.processHeaderDocument(headerDocument);
 
-              // Don't continue processing files whose header
-              // document is invalid - the entire file is excempt
-              // from data in this case.
-              if (!header) {
-                return;
+              try {
+                headerAggregate.close()
+              } catch (caughtError) {
+                caughtError.message = `(${colors.yellow(`header`)}) ${caughtError.message}`;
+                fileAggregate.push(caughtError);
               }
 
-              const entries = map(
-                entryDocuments
-                  .filter(Boolean)
-                  .map((document) => ({file, document})),
-                decorateErrorWithFile(
-                  decorateErrorWithIndex(({document}) =>
-                    dataStep.processEntryDocument(document))),
-                {message: `Errors processing entry documents`});
-
-              // Entries may be incomplete (i.e. any errored
-              // documents won't have a processed output
-              // represented here) - this is intentional! By
-              // principle, partial output is preferred over
-              // erroring an entire file.
-              processResults.push({header, entries});
-            });
-          });
-        }
+              const entryObjects = [];
 
-        if (documentMode === documentModes.onePerFile) {
-          nest({message: `Errors processing data files as valid documents`}, ({call}) => {
-            processResults = [];
+              for (let index = 0; index < entryDocuments.length; index++) {
+                const entryDocument = entryDocuments[index];
 
-            yamlResults.forEach(({file, documents}) => {
-              if (documents.length > 1) {
-                call(decorateErrorWithFile(() => {
-                  throw new Error(`Only expected one document to be present per file`);
-                }), {file});
-                return;
-              } else if (empty(documents) || !documents[0]) {
-                call(decorateErrorWithFile(() => {
-                  throw new Error(`Expected a document, this file is empty`);
-                }), {file});
-              }
+                const {thing: entryObject, aggregate: entryAggregate} =
+                  dataStep.processEntryDocument(entryDocument);
 
-              const result = call(
-                decorateErrorWithFile(({document}) =>
-                  dataStep.processDocument(document)),
-                {file, document: documents[0]});
+                entryObjects.push(entryObject);
 
-              if (!result) {
-                return;
+                try {
+                  entryAggregate.close();
+                } catch (caughtError) {
+                  caughtError.message = `(${colors.yellow(`entry #${index + 1}`)}) ${caughtError.message}`;
+                  fileAggregate.push(caughtError);
+                }
               }
 
-              processResults.push(result);
-            });
-          });
+              processResults.push({
+                header: headerObject,
+                entries: entryObjects,
+              });
+
+              fileAggregate.close();
+            }), {message: `Errors processing documents in data files`});
+            break;
+
+          case documentModes.onePerFile:
+            map(yamlResults, decorateErrorWithFile(({documents}) => {
+              if (documents.length > 1)
+                throw new Error(`Only expected one document to be present per file, got ${documents.length} here`);
+
+              if (empty(documents) || !documents[0])
+                throw new Error(`Expected a document, this file is empty`);
+
+              const {thing, aggregate} =
+                dataStep.processDocument(documents[0]);
+
+              processResults.push(thing);
+              aggregate.close();
+            }), {message: `Errors processing data files as valid documents`});
+            break;
         }
 
         const saveResult = call(dataStep.save, processResults);
@@ -1316,13 +1450,27 @@ export async function loadAndProcessDataDocuments({dataPath}) {
 
 // Data linking! Basically, provide (portions of) wikiData to the Things which
 // require it - they'll expose dynamically computed properties as a result (many
-// of which are required for page HTML generation).
-export function linkWikiDataArrays(wikiData) {
+// of which are required for page HTML generation and other expected behavior).
+//
+// The XXX_decacheWikiData option should be used specifically to mark
+// points where you *aren't* replacing any of the arrays under wikiData with
+// new values, and are using linkWikiDataArrays to instead "decache" data
+// properties which depend on any of them. It's currently not possible for
+// a CacheableObject to depend directly on the value of a property exposed
+// on some other CacheableObject, so when those values change, you have to
+// manually decache before the object will realize its cache isn't valid
+// anymore.
+export function linkWikiDataArrays(wikiData, {
+  XXX_decacheWikiData = false,
+} = {}) {
   function assignWikiData(things, ...keys) {
+    if (things === undefined) return;
     for (let i = 0; i < things.length; i++) {
       const thing = things[i];
       for (let j = 0; j < keys.length; j++) {
         const key = keys[j];
+        if (!(key in wikiData)) continue;
+        if (XXX_decacheWikiData) thing[key] = [];
         thing[key] = wikiData[key];
       }
     }
@@ -1340,7 +1488,7 @@ export function linkWikiDataArrays(wikiData) {
   assignWikiData(WD.flashData, 'artistData', 'flashActData', 'trackData');
   assignWikiData(WD.flashActData, 'flashData');
   assignWikiData(WD.artTagData, 'albumData', 'trackData');
-  assignWikiData(WD.homepageLayout.rows, 'albumData', 'groupData');
+  assignWikiData(WD.homepageLayout?.rows, 'albumData', 'groupData');
 }
 
 export function sortWikiDataArrays(wikiData) {
@@ -1368,7 +1516,9 @@ export function filterDuplicateDirectories(wikiData) {
   const deduplicateSpec = [
     'albumData',
     'artTagData',
+    'artistData',
     'flashData',
+    'flashActData',
     'groupData',
     'newsData',
     'trackData',
@@ -1377,7 +1527,7 @@ export function filterDuplicateDirectories(wikiData) {
   const aggregate = openAggregate({message: `Duplicate directories found`});
   for (const thingDataProp of deduplicateSpec) {
     const thingData = wikiData[thingDataProp];
-    aggregate.nest({message: `Duplicate directories found in ${color.green('wikiData.' + thingDataProp)}`}, ({call}) => {
+    aggregate.nest({message: `Duplicate directories found in ${colors.green('wikiData.' + thingDataProp)}`}, ({call}) => {
       const directoryPlaces = Object.create(null);
       const duplicateDirectories = [];
 
@@ -1403,7 +1553,7 @@ export function filterDuplicateDirectories(wikiData) {
         const places = directoryPlaces[directory];
         call(() => {
           throw new Error(
-            `Duplicate directory ${color.green(directory)}:\n` +
+            `Duplicate directory ${colors.green(directory)}:\n` +
               places.map((thing) => ` - ` + inspect(thing)).join('\n')
           );
         });
@@ -1444,45 +1594,45 @@ export function filterDuplicateDirectories(wikiData) {
 export function filterReferenceErrors(wikiData) {
   const referenceSpec = [
     ['wikiInfo', processWikiInfoDocument, {
-      divideTrackListsByGroupsByRef: 'group',
+      divideTrackListsByGroups: 'group',
     }],
 
     ['albumData', processAlbumDocument, {
-      artistContribsByRef: '_contrib',
-      coverArtistContribsByRef: '_contrib',
-      trackCoverArtistContribsByRef: '_contrib',
-      wallpaperArtistContribsByRef: '_contrib',
-      bannerArtistContribsByRef: '_contrib',
-      groupsByRef: 'group',
-      artTagsByRef: 'artTag',
+      artistContribs: '_contrib',
+      coverArtistContribs: '_contrib',
+      trackCoverArtistContribs: '_contrib',
+      wallpaperArtistContribs: '_contrib',
+      bannerArtistContribs: '_contrib',
+      groups: 'group',
+      artTags: 'artTag',
     }],
 
     ['trackData', processTrackDocument, {
-      artistContribsByRef: '_contrib',
-      contributorContribsByRef: '_contrib',
-      coverArtistContribsByRef: '_contrib',
-      referencedTracksByRef: '_trackNotRerelease',
-      sampledTracksByRef: '_trackNotRerelease',
-      artTagsByRef: 'artTag',
-      originalReleaseTrackByRef: '_trackNotRerelease',
+      artistContribs: '_contrib',
+      contributorContribs: '_contrib',
+      coverArtistContribs: '_contrib',
+      referencedTracks: '_trackNotRerelease',
+      sampledTracks: '_trackNotRerelease',
+      artTags: 'artTag',
+      originalReleaseTrack: '_trackNotRerelease',
     }],
 
     ['groupCategoryData', processGroupCategoryDocument, {
-      groupsByRef: 'group',
+      groups: 'group',
     }],
 
     ['homepageLayout.rows', undefined, {
-      sourceGroupByRef: 'group',
-      sourceAlbumsByRef: 'album',
+      sourceGroup: '_homepageSourceGroup',
+      sourceAlbums: 'album',
     }],
 
     ['flashData', processFlashDocument, {
-      contributorContribsByRef: '_contrib',
-      featuredTracksByRef: 'track',
+      contributorContribs: '_contrib',
+      featuredTracks: 'track',
     }],
 
     ['flashActData', processFlashActDocument, {
-      flashesByRef: 'flash',
+      flashes: 'flash',
     }],
   ];
 
@@ -1498,7 +1648,7 @@ export function filterReferenceErrors(wikiData) {
   for (const [thingDataProp, providedProcessDocumentFn, propSpec] of referenceSpec) {
     const thingData = getNestedProp(wikiData, thingDataProp);
 
-    aggregate.nest({message: `Reference errors in ${color.green('wikiData.' + thingDataProp)}`}, ({nest}) => {
+    aggregate.nest({message: `Reference errors in ${colors.green('wikiData.' + thingDataProp)}`}, ({nest}) => {
       const things = Array.isArray(thingData) ? thingData : [thingData];
 
       for (const thing of things) {
@@ -1514,10 +1664,10 @@ export function filterReferenceErrors(wikiData) {
 
         nest({message: `Reference errors in ${inspect(thing)}`}, ({push, filter}) => {
           for (const [property, findFnKey] of Object.entries(propSpec)) {
-            const value = thing[property];
+            const value = CacheableObject.getUpdateValue(thing, property);
 
             if (value === undefined) {
-              push(new TypeError(`Property ${color.red(property)} isn't valid for ${color.green(thing.constructor.name)}`));
+              push(new TypeError(`Property ${colors.red(property)} isn't valid for ${colors.green(thing.constructor.name)}`));
               continue;
             }
 
@@ -1534,23 +1684,34 @@ export function filterReferenceErrors(wikiData) {
                   if (alias) {
                     // No need to check if the original exists here. Aliases are automatically
                     // created from a field on the original, so the original certainly exists.
-                    const original = find.artist(alias.aliasedArtistRef, wikiData.artistData, {mode: 'quiet'});
-                    throw new Error(`Reference ${color.red(contribRef.who)} is to an alias, should be ${color.green(original.name)}`);
+                    const original = alias.aliasedArtist;
+                    throw new Error(`Reference ${colors.red(contribRef.who)} is to an alias, should be ${colors.green(original.name)}`);
                   }
 
                   return boundFind.artist(contribRef.who);
                 };
                 break;
 
+              case '_homepageSourceGroup':
+                findFn = groupRef => {
+                  if (groupRef === 'new-additions' || groupRef === 'new-releases') {
+                    return true;
+                  }
+
+                  return boundFind.group(groupRef);
+                };
+                break;
+
               case '_trackNotRerelease':
                 findFn = trackRef => {
                   const track = find.track(trackRef, wikiData.trackData, {mode: 'error'});
+                  const originalRef = track && CacheableObject.getUpdateValue(track, 'originalReleaseTrack');
 
-                  if (track?.originalReleaseTrackByRef) {
+                  if (originalRef) {
                     // It's possible for the original to not actually exist, in this case.
                     // It should still be reported since the 'Originally Released As' field
                     // was present.
-                    const original = find.track(track.originalReleaseTrackByRef, wikiData.trackData, {mode: 'quiet'});
+                    const original = find.track(originalRef, wikiData.trackData, {mode: 'quiet'});
 
                     // Prefer references by name, but only if it's unambiguous.
                     const originalByName =
@@ -1560,12 +1721,12 @@ export function filterReferenceErrors(wikiData) {
 
                     const shouldBeMessage =
                       (originalByName
-                        ? color.green(original.name)
+                        ? colors.green(original.name)
                      : original
-                        ? color.green('track:' + original.directory)
-                        : color.green(track.originalReleaseTrackByRef));
+                        ? colors.green('track:' + original.directory)
+                        : colors.green(originalRef));
 
-                    throw new Error(`Reference ${color.red(trackRef)} is to a rerelease, should be ${shouldBeMessage}`);
+                    throw new Error(`Reference ${colors.red(trackRef)} is to a rerelease, should be ${shouldBeMessage}`);
                   }
 
                   return track;
@@ -1578,7 +1739,7 @@ export function filterReferenceErrors(wikiData) {
             }
 
             const suppress = fn => conditionallySuppressError(error => {
-              if (property === 'sampledTracksByRef') {
+              if (property === 'sampledTracks') {
                 // Suppress "didn't match anything" errors in particular, just for samples.
                 // In hsmusic-data we have a lot of "stub" sample data which don't have
                 // corresponding tracks yet, so it won't be useful to report such reference
@@ -1596,13 +1757,13 @@ export function filterReferenceErrors(wikiData) {
 
             const fieldPropertyMessage =
               (processDocumentFn?.propertyFieldMapping?.[property]
-                ? ` in field ${color.green(processDocumentFn.propertyFieldMapping[property])}`
-                : ` in property ${color.green(property)}`);
+                ? ` in field ${colors.green(processDocumentFn.propertyFieldMapping[property])}`
+                : ` in property ${colors.green(property)}`);
 
             const findFnMessage =
               (findFnKey.startsWith('_')
                 ? ``
-                : ` (${color.green('find.' + findFnKey)})`);
+                : ` (${colors.green('find.' + findFnKey)})`);
 
             const errorMessage =
               (Array.isArray(value)
diff --git a/src/file-size-preloader.js b/src/file-size-preloader.js
index 38e60e67..4eadde7b 100644
--- a/src/file-size-preloader.js
+++ b/src/file-size-preloader.js
@@ -29,6 +29,8 @@ export default class FileSizePreloader {
   #loadingPromise = null;
   #resolveLoadingPromise = null;
 
+  hadErrored = false;
+
   loadPaths(...paths) {
     this.#paths.push(...paths.filter((p) => !this.#paths.includes(p)));
     return this.#startLoadingPaths();
@@ -67,6 +69,7 @@ export default class FileSizePreloader {
       // Oops! Discard that path, and don't increment the index before
       // moving on, since the next path will now be in its place.
       this.#paths.splice(this.#loadedPathIndex + 1, 1);
+      this.hasErrored = true;
       logWarn`Failed to process file size for ${path}: ${error.message}`;
       return this.#loadNextPath();
     }
diff --git a/src/find.js b/src/find.js
index b8230800..8c9413b7 100644
--- a/src/find.js
+++ b/src/find.js
@@ -1,6 +1,7 @@
 import {inspect} from 'node:util';
 
-import {color, logWarn} from '#cli';
+import {colors, logWarn} from '#cli';
+import {typeAppearance} from '#sugar';
 
 function warnOrThrow(mode, message) {
   if (mode === 'error') {
@@ -14,115 +15,169 @@ function warnOrThrow(mode, message) {
   return null;
 }
 
-function findHelper(keys, findFns = {}) {
+export function processAllAvailableMatches(data, {
+  getMatchableNames = thing =>
+    (Object.hasOwn(thing, 'name')
+      ? [thing.name]
+      : []),
+} = {}) {
+  const byName = Object.create(null);
+  const byDirectory = Object.create(null);
+  const multipleNameMatches = Object.create(null);
+
+  for (const thing of data) {
+    for (const name of getMatchableNames(thing)) {
+      if (typeof name !== 'string') {
+        logWarn`Unexpected ${typeAppearance(name)} returned in names for ${inspect(thing)}`;
+        continue;
+      }
+
+      const normalizedName = name.toLowerCase();
+      if (normalizedName in byName) {
+        const alreadyMatchesByName = byName[normalizedName];
+        byName[normalizedName] = null;
+        if (normalizedName in multipleNameMatches) {
+          multipleNameMatches[normalizedName].push(thing);
+        } else {
+          multipleNameMatches[normalizedName] = [alreadyMatchesByName, thing];
+        }
+      } else {
+        byName[normalizedName] = thing;
+      }
+    }
+
+    byDirectory[thing.directory] = thing;
+  }
+
+  return {byName, byDirectory, multipleNameMatches};
+}
+
+function findHelper({
+  referenceTypes,
+
+  getMatchableNames = undefined,
+}) {
+  const keyRefRegex =
+    new RegExp(String.raw`^(?:(${referenceTypes.join('|')}):(?=\S))?(.*)$`);
+
   // Note: This cache explicitly *doesn't* support mutable data arrays. If the
   // data array is modified, make sure it's actually a new array object, not
   // the original, or the cache here will break and act as though the data
   // hasn't changed!
   const cache = new WeakMap();
 
-  const byDirectory = findFns.byDirectory || matchDirectory;
-  const byName = findFns.byName || matchName;
-
-  const keyRefRegex = new RegExp(String.raw`^(?:(${keys.join('|')}):(?=\S))?(.*)$`);
-
   // The mode argument here may be 'warn', 'error', or 'quiet'. 'error' throws
   // errors for null matches (with details about the error), while 'warn' and
   // 'quiet' both return null, with 'warn' logging details directly to the
   // console.
-  return (fullRef, data, {mode = 'warn'} = {}) => {
+  return (fullRef, data, {mode = 'warn'}) => {
     if (!fullRef) return null;
     if (typeof fullRef !== 'string') {
-      throw new Error(`Got a reference that is ${typeof fullRef}, not string: ${fullRef}`);
+      throw new TypeError(`Expected a string, got ${typeAppearance(fullRef)}`);
     }
 
     if (!data) {
-      throw new Error(`Expected data to be present`);
+      throw new TypeError(`Expected data to be present`);
     }
 
-    if (!Array.isArray(data) && data.wikiData) {
-      throw new Error(`Old {wikiData: {...}} format provided`);
-    }
+    let subcache = cache.get(data);
+    if (!subcache) {
+      subcache =
+        processAllAvailableMatches(data, {
+          getMatchableNames,
+        });
 
-    let cacheForThisData = cache.get(data);
-    const cachedValue = cacheForThisData?.[fullRef];
-    if (cachedValue) {
-      globalThis.NUM_CACHE = (globalThis.NUM_CACHE || 0) + 1;
-      return cachedValue;
-    }
-    if (!cacheForThisData) {
-      cacheForThisData = Object.create(null);
-      cache.set(data, cacheForThisData);
+      cache.set(data, subcache);
     }
 
-    const match = fullRef.match(keyRefRegex);
-    if (!match) {
-      return warnOrThrow(mode, `Malformed link reference: "${fullRef}"`);
+    const regexMatch = fullRef.match(keyRefRegex);
+    if (!regexMatch) {
+      warnOrThrow(mode, `Malformed link reference: "${fullRef}"`);
     }
 
-    const key = match[1];
-    const ref = match[2];
-
-    const found = key ? byDirectory(ref, data, mode) : byName(ref, data, mode);
-
-    if (!found) {
-      warnOrThrow(mode, `Didn't match anything for ${color.bright(fullRef)}`);
+    const typePart = regexMatch[1];
+    const refPart = regexMatch[2];
+
+    const normalizedName =
+      (typePart
+        ? null
+        : refPart.toLowerCase());
+
+    const match =
+      (typePart
+        ? subcache.byDirectory[refPart]
+        : subcache.byName[normalizedName]);
+
+    if (!match && !typePart) {
+      if (subcache.multipleNameMatches[normalizedName]) {
+        return warnOrThrow(mode,
+          `Multiple matches for reference "${fullRef}". Please resolve:\n` +
+          subcache.multipleNameMatches[normalizedName]
+            .map(match => `- ${inspect(match)}\n`)
+            .join('') +
+          `Returning null for this reference.`);
+      }
     }
 
-    cacheForThisData[fullRef] = found;
+    if (!match) {
+      warnOrThrow(mode, `Didn't match anything for ${colors.bright(fullRef)}`);
+      return null;
+    }
 
-    return found;
+    return match;
   };
 }
 
-function matchDirectory(ref, data) {
-  return data.find(({directory}) => directory === ref);
-}
-
-function matchName(ref, data, mode) {
-  const matches = data.filter(
-    ({name}) => name.toLowerCase() === ref.toLowerCase()
-  );
-
-  if (matches.length > 1) {
-    return warnOrThrow(
-      mode,
-      `Multiple matches for reference "${ref}". Please resolve:\n` +
-        matches.map((match) => `- ${inspect(match)}\n`).join('') +
-        `Returning null for this reference.`
-    );
-  }
-
-  if (matches.length === 0) {
-    return null;
-  }
-
-  const thing = matches[0];
-
-  if (ref !== thing.name) {
-    warnOrThrow(
-      mode,
-      `Bad capitalization: ${color.red(ref)} -> ${color.green(thing.name)}`
-    );
-  }
-
-  return thing;
-}
-
-function matchTagName(ref, data, quiet) {
-  return matchName(ref.startsWith('cw: ') ? ref.slice(4) : ref, data, quiet);
-}
-
 const find = {
-  album: findHelper(['album', 'album-commentary', 'album-gallery']),
-  artist: findHelper(['artist', 'artist-gallery']),
-  artTag: findHelper(['tag'], {byName: matchTagName}),
-  flash: findHelper(['flash']),
-  group: findHelper(['group', 'group-gallery']),
-  listing: findHelper(['listing']),
-  newsEntry: findHelper(['news-entry']),
-  staticPage: findHelper(['static']),
-  track: findHelper(['track']),
+  album: findHelper({
+    referenceTypes: ['album', 'album-commentary', 'album-gallery'],
+  }),
+
+  artist: findHelper({
+    referenceTypes: ['artist', 'artist-gallery'],
+  }),
+
+  artTag: findHelper({
+    referenceTypes: ['tag'],
+
+    getMatchableNames: tag =>
+      (tag.isContentWarning
+        ? [`cw: ${tag.name}`]
+        : [tag.name]),
+  }),
+
+  flash: findHelper({
+    referenceTypes: ['flash'],
+  }),
+
+  flashAct: findHelper({
+    referenceTypes: ['flash-act'],
+  }),
+
+  group: findHelper({
+    referenceTypes: ['group', 'group-gallery'],
+  }),
+
+  listing: findHelper({
+    referenceTypes: ['listing'],
+  }),
+
+  newsEntry: findHelper({
+    referenceTypes: ['news-entry'],
+  }),
+
+  staticPage: findHelper({
+    referenceTypes: ['static'],
+  }),
+
+  track: findHelper({
+    referenceTypes: ['track'],
+
+    getMatchableNames: track =>
+      (track.alwaysReferenceByDirectory
+        ? []
+        : [track.name]),
+  }),
 };
 
 export default find;
@@ -139,6 +194,7 @@ export function bindFind(wikiData, opts1) {
       artist: 'artistData',
       artTag: 'artTagData',
       flash: 'flashData',
+      flashAct: 'flashActData',
       group: 'groupData',
       listing: 'listingSpec',
       newsEntry: 'newsData',
@@ -155,7 +211,9 @@ export function bindFind(wikiData, opts1) {
                 ? findFn(ref, thingData, {...opts1, ...opts2})
                 : findFn(ref, thingData, opts1)
           : (ref, opts2) =>
-              opts2 ? findFn(ref, thingData, opts2) : findFn(ref, thingData),
+              opts2
+                ? findFn(ref, thingData, opts2)
+                : findFn(ref, thingData),
       ];
     })
   );
diff --git a/src/gen-thumbs.js b/src/gen-thumbs.js
index e9932822..3d441bc9 100644
--- a/src/gen-thumbs.js
+++ b/src/gen-thumbs.js
@@ -74,7 +74,7 @@
 
 'use strict';
 
-const CACHE_FILE = 'thumbnail-cache.json';
+export const CACHE_FILE = 'thumbnail-cache.json';
 const WARNING_DELAY_TIME = 10000;
 
 const thumbnailSpec = {
@@ -91,8 +91,13 @@ import {createReadStream} from 'node:fs';
 import {readFile, stat, unlink, writeFile} from 'node:fs/promises';
 import * as path from 'node:path';
 
+import dimensionsOf from 'image-size';
+
+import {delay, empty, queue} from '#sugar';
+import {CacheableObject} from '#things';
+
 import {
-  color,
+  colors,
   fileIssue,
   logError,
   logInfo,
@@ -108,10 +113,119 @@ import {
   traverse,
 } from '#node-utils';
 
-import {delay, empty, queue} from '#sugar';
-
 export const defaultMagickThreads = 8;
 
+export function getThumbnailsAvailableForDimensions([width, height]) {
+  // This function is intended to be portable, so it can be used both for
+  // calculating which thumbnails to generate, and which ones will be ready
+  // to reference in generated code. Sizes are in array [name, size] form
+  // with larger sizes earlier in return. Keep in mind this isn't a direct
+  // 1:1 mapping with the sizes listed in the thumbnail spec, because the
+  // largest thumbnail (first in return) will be adjusted to the provided
+  // dimensions.
+
+  const {all} = getThumbnailsAvailableForDimensions;
+
+  // Find the largest size which is beneath the passed dimensions. We use the
+  // longer edge here (of width and height) so that each resulting thumbnail is
+  // fully constrained within the size*size square defined by its spec.
+  const longerEdge = Math.max(width, height);
+  const index = all.findIndex(([name, size]) => size <= longerEdge);
+
+  // Literal edge cases are handled specially. For dimensions which are bigger
+  // than the biggest thumbnail in the spec, return all possible results.
+  // These don't need any adjustments since the largest is already smaller than
+  // the provided dimensions.
+  if (index === 0) {
+    return [
+      ...all,
+    ];
+  }
+
+  // For dimensions which are smaller than the smallest thumbnail, return only
+  // the smallest, adjusted to the provided dimensions.
+  if (index === -1) {
+    const smallest = all[all.length - 1];
+    return [
+      [smallest[0], longerEdge],
+    ];
+  }
+
+  // For non-edge cases, we return the largest size below the dimensions
+  // as well as everything smaller, but also the next size larger - that way
+  // there's a size which is as big as the original, but still JPEG compressed.
+  // The size larger is adjusted to the provided dimensions to represent the
+  // actual dimensions it'll provide.
+  const larger = all[index - 1];
+  const rest = all.slice(index);
+  return [
+    [larger[0], longerEdge],
+    ...rest,
+  ];
+}
+
+getThumbnailsAvailableForDimensions.all =
+  Object.entries(thumbnailSpec)
+    .map(([name, {size}]) => [name, size])
+    .sort((a, b) => b[1] - a[1]);
+
+function getCacheEntryForMediaPath(mediaPath, cache) {
+  // Gets the cache entry for the provided image path, which should always be
+  // a forward-slashes path (i.e. suitable for display online). Since the cache
+  // file may have forward or back-slashes, this checks both.
+
+  const entryFromMediaPath = cache[mediaPath];
+  if (entryFromMediaPath) return entryFromMediaPath;
+
+  const winPath = mediaPath.split(path.posix.sep).join(path.win32.sep);
+  const entryFromWinPath = cache[winPath];
+  if (entryFromWinPath) return entryFromWinPath;
+
+  return null;
+}
+
+export function checkIfImagePathHasCachedThumbnails(mediaPath, cache) {
+  // Generic utility for checking if the thumbnail cache includes any info for
+  // the provided image path, so that the other functions don't hard-code the
+  // cache format.
+
+  return !!getCacheEntryForMediaPath(mediaPath, cache);
+}
+
+export function getDimensionsOfImagePath(mediaPath, cache) {
+  // This function is really generic. It takes the gen-thumbs image cache and
+  // returns the dimensions in that cache, so that other functions don't need
+  // to hard-code the cache format.
+
+  const cacheEntry = getCacheEntryForMediaPath(mediaPath, cache);
+
+  if (!cacheEntry) {
+    throw new Error(`Expected mediaPath to be included in cache, got ${mediaPath}`);
+  }
+
+  const [width, height] = cacheEntry.slice(1);
+  return [width, height];
+}
+
+export function getThumbnailEqualOrSmaller(preferred, mediaPath, cache) {
+  // This function is totally exclusive to page generation. It's a shorthand
+  // for accessing dimensions from the thumbnail cache, calculating all the
+  // thumbnails available, and selecting the one which is equal to or smaller
+  // than the provided size. Since the path provided might not be the actual
+  // one which is being thumbnail-ified, this just returns the name of the
+  // selected thumbnail size.
+
+  if (!getCacheEntryForMediaPath(mediaPath, cache)) {
+    throw new Error(`Expected mediaPath to be included in cache, got ${mediaPath}`);
+  }
+
+  const {size: preferredSize} = thumbnailSpec[preferred];
+  const [width, height] = getDimensionsOfImagePath(mediaPath, cache);
+  const available = getThumbnailsAvailableForDimensions([width, height]);
+  const [selected] = available.find(([name, size]) => size <= preferredSize);
+  return selected;
+}
+
 function readFileMD5(filePath) {
   return new Promise((resolve, reject) => {
     const md5 = createHash('md5');
@@ -122,15 +236,26 @@ function readFileMD5(filePath) {
   });
 }
 
-async function getImageMagickVersion(spawnConvert) {
-  const proc = spawnConvert(['--version'], false);
+async function identifyImageDimensions(filePath) {
+  // See: https://github.com/image-size/image-size/issues/96
+  const buffer = await readFile(filePath);
+  const dimensions = dimensionsOf(buffer);
+  return [dimensions.width, dimensions.height];
+}
+
+async function getImageMagickVersion(binary) {
+  const proc = spawn(binary, ['--version']);
 
   let allData = '';
   proc.stdout.on('data', (data) => {
     allData += data.toString();
   });
 
-  await promisifyProcess(proc, false);
+  try {
+    await promisifyProcess(proc, false);
+  } catch (error) {
+    return null;
+  }
 
   if (!allData.match(/ImageMagick/i)) {
     return null;
@@ -144,29 +269,45 @@ async function getImageMagickVersion(spawnConvert) {
   return match[1];
 }
 
-async function getSpawnConvert() {
-  let fn, description, version;
-  if (await commandExists('convert')) {
-    fn = (args) => spawn('convert', args);
-    description = 'convert';
-  } else if (await commandExists('magick')) {
-    fn = (args, prefix = true) =>
-      spawn('magick', prefix ? ['convert', ...args] : args);
-    description = 'magick convert';
-  } else {
-    return [`no convert or magick binary`, null];
+async function getSpawnMagick(tool) {
+  if (tool !== 'identify' && tool !== 'convert') {
+    throw new Error(`Expected identify or convert`);
+  }
+
+  let fn = null;
+  let description = null;
+  let version = null;
+
+  if (await commandExists(tool)) {
+    version = await getImageMagickVersion(tool);
+    if (version !== null) {
+      fn = (args) => spawn(tool, args);
+      description = tool;
+    }
   }
 
-  version = await getImageMagickVersion(fn);
+  if (fn === null && await commandExists('magick')) {
+    version = await getImageMagickVersion('magick');
+    if (version !== null) {
+      fn = (args) => spawn('magick', [tool, ...args]);
+      description = `magick ${tool}`;
+    }
+  }
 
-  if (version === null) {
-    return [`binary --version output didn't indicate it's ImageMagick`];
+  if (fn === null) {
+    return [`no ${tool} or magick binary`, null];
   }
 
   return [`${description} (${version})`, fn];
 }
 
-function generateImageThumbnails(filePath, {spawnConvert}) {
+// Note: This returns an array of no-argument functions, suitable for passing
+// to queue().
+function generateImageThumbnails({
+  filePath,
+  dimensions,
+  spawnConvert,
+}) {
   const dirname = path.dirname(filePath);
   const extname = path.extname(filePath);
   const basename = path.basename(filePath, extname);
@@ -185,10 +326,11 @@ function generateImageThumbnails(filePath, {spawnConvert}) {
       output(name),
     ]);
 
-  return Promise.all(
-    Object.entries(thumbnailSpec)
-      .map(([ext, details]) =>
-        promisifyProcess(convert('.' + ext, details), false)));
+  return (
+    getThumbnailsAvailableForDimensions(dimensions)
+      .map(([name]) => [name, thumbnailSpec[name]])
+      .map(([name, details]) => () =>
+        promisifyProcess(convert('.' + name, details), false)));
 }
 
 export async function clearThumbs(mediaPath, {
@@ -224,7 +366,7 @@ export async function clearThumbs(mediaPath, {
         console.error(file);
       }
       fileIssue();
-      return;
+      return {success: false};
     }
 
     logInfo`Clearing out ${thumbFiles.length} thumbs.`;
@@ -249,6 +391,7 @@ export async function clearThumbs(mediaPath, {
         console.error(file);
       }
       logError`Check for permission errors?`;
+      return {success: false};
     } else {
       logInfo`Successfully deleted all ${thumbFiles.length} thumbnail files!`;
     }
@@ -277,6 +420,8 @@ export async function clearThumbs(mediaPath, {
       logWarn`Failed to remove cache file. Check its permissions?`;
     }
   }
+
+  return {success: true};
 }
 
 export default async function genThumbs(mediaPath, {
@@ -290,18 +435,21 @@ export default async function genThumbs(mediaPath, {
 
   const quietInfo = quiet ? () => null : logInfo;
 
-  const [convertInfo, spawnConvert] = (await getSpawnConvert()) ?? [];
+  const [convertInfo, spawnConvert] = await getSpawnMagick('convert');
+
   if (!spawnConvert) {
     logError`${`It looks like you don't have ImageMagick installed.`}`;
     logError`ImageMagick is required to generate thumbnails for display on the wiki.`;
-    logError`(Error message: ${convertInfo})`;
+    for (const error of [convertInfo].filter(Boolean)) {
+      logError`(Error message: ${error})`;
+    }
     logInfo`You can find info to help install ImageMagick on Linux, Windows, or macOS`;
     logInfo`from its official website: ${`https://imagemagick.org/script/download.php`}`;
     logInfo`If you have trouble working ImageMagick and would like some help, feel free`;
     logInfo`to drop a message in the HSMusic Discord server! ${'https://hsmusic.wiki/discord/'}`;
-    return false;
+    return {success: false};
   } else {
-    logInfo`Found ImageMagick binary: ${convertInfo}`;
+    logInfo`Found ImageMagick binary:  ${convertInfo}`;
   }
 
   quietInfo`Running up to ${magickThreads + ' magick threads'} simultaneously.`;
@@ -341,19 +489,16 @@ export default async function genThumbs(mediaPath, {
 
   const imagePaths = await traverseSourceImagePaths(mediaPath, {target: 'generate'});
 
-  const imageToMD5Entries = await progressPromiseAll(
-    `Generating MD5s of image files`,
-    queue(
-      imagePaths.map(
-        (imagePath) => () =>
-          readFileMD5(path.join(mediaPath, imagePath)).then(
-            (md5) => [imagePath, md5],
-            (error) => [imagePath, {error}]
-          )
-      ),
-      queueSize
-    )
-  );
+  const imageToMD5Entries =
+    await progressPromiseAll(
+      `Generating MD5s of image files`,
+      queue(
+        imagePaths.map(imagePath => () =>
+          readFileMD5(path.join(mediaPath, imagePath))
+            .then(
+              md5 => [imagePath, md5],
+              error => [imagePath, {error}])),
+        queueSize));
 
   {
     let error = false;
@@ -367,23 +512,53 @@ export default async function genThumbs(mediaPath, {
       logError`Failed to read at least one image file!`;
       logError`This implies a thumbnail probably won't be generatable.`;
       logError`So, exiting early.`;
-      return false;
+      return {success: false};
     } else {
       quietInfo`All image files successfully read.`;
     }
   }
 
+  const imageToDimensionsEntries =
+    await progressPromiseAll(
+      `Identifying dimensions of image files`,
+      queue(
+        imagePaths.map(imagePath => () =>
+          identifyImageDimensions(path.join(mediaPath, imagePath))
+            .then(
+              dimensions => [imagePath, dimensions],
+              error => [imagePath, {error}])),
+        queueSize));
+
+  {
+    let error = false;
+    for (const entry of imageToDimensionsEntries) {
+      if (entry[1].error) {
+        logError`Failed to identify dimensions ${entry[0]}: ${entry[1].error}`;
+        error = true;
+      }
+    }
+    if (error) {
+      logError`Failed to identify dimensions of at least one image file!`;
+      logError`This implies a thumbnail probably won't be generatable.`;
+      logError`So, exiting early.`;
+      return {success: false};
+    } else {
+      quietInfo`All image files successfully had dimensions identified.`;
+    }
+  }
+
+  const imageToDimensions = Object.fromEntries(imageToDimensionsEntries);
+
   // Technically we could pro8a8ly mut8te the cache varia8le in-place?
   // 8ut that seems kinda iffy.
   const updatedCache = Object.assign({}, cache);
 
   const entriesToGenerate = imageToMD5Entries.filter(
-    ([filePath, md5]) => md5 !== cache[filePath]
-  );
+    ([filePath, md5]) => md5 !== cache[filePath]?.[0]);
 
   if (empty(entriesToGenerate)) {
     logInfo`All image thumbnails are already up-to-date - nice!`;
-    return true;
+    return {success: true, cache};
   }
 
   logInfo`Generating thumbnails for ${entriesToGenerate.length} media files.`;
@@ -392,31 +567,45 @@ export default async function genThumbs(mediaPath, {
   }
 
   const failed = [];
-  const succeeded = [];
+
   const writeMessageFn = () =>
     `Writing image thumbnails. [failed: ${failed.length}]`;
 
+  const generateCalls =
+    entriesToGenerate.flatMap(([filePath, md5]) =>
+      generateImageThumbnails({
+        filePath: path.join(mediaPath, filePath),
+        dimensions: imageToDimensions[filePath],
+        spawnConvert,
+      }).map(call => async () => {
+        try {
+          await call();
+        } catch (error) {
+          failed.push([filePath, error]);
+        }
+      }));
+
   await progressPromiseAll(writeMessageFn,
-    queue(
-      entriesToGenerate.map(([filePath, md5]) => () =>
-        generateImageThumbnails(path.join(mediaPath, filePath), {spawnConvert}).then(
-          () => {
-            updatedCache[filePath] = md5;
-            succeeded.push(filePath);
-          },
-          error => {
-            failed.push([filePath, error]);
-          })),
-      magickThreads));
+    queue(generateCalls, magickThreads));
+
+  // Sort by file path.
+  failed.sort(([a], [b]) => a < b ? -1 : a > b ? 1 : 0);
+
+  const failedFilePaths = new Set(failed.map(([filePath]) => filePath));
+
+  for (const [filePath, md5] of entriesToGenerate) {
+    if (failedFilePaths.has(filePath)) continue;
+    updatedCache[filePath] = [md5, ...imageToDimensions[filePath]];
+  }
 
   if (empty(failed)) {
     logInfo`Generated all (updated) thumbnails successfully!`;
   } else {
     for (const [path, error] of failed) {
-      logError`Thumbnails failed to generate for ${path} - ${error}`;
+      logError`Thumbnail failed to generate for ${path} - ${error}`;
     }
-    logWarn`Result is incomplete - the above ${failed.length} thumbnails should be checked for errors.`;
-    logWarn`${succeeded.length} successfully generated images won't be regenerated next run, though!`;
+    logWarn`Result is incomplete - the above thumbnails should be checked for errors.`;
+    logWarn`Successfully generated images won't be regenerated next run, though!`;
   }
 
   try {
@@ -431,7 +620,7 @@ export default async function genThumbs(mediaPath, {
     logWarn`Sorry about that!`;
   }
 
-  return true;
+  return {success: true, cache: updatedCache};
 }
 
 export function getExpectedImagePaths(mediaPath, {urls, wikiData}) {
@@ -441,8 +630,8 @@ export function getExpectedImagePaths(mediaPath, {urls, wikiData}) {
     wikiData.albumData
       .flatMap(album => [
         album.hasCoverArt && fromRoot.to('media.albumCover', album.directory, album.coverArtFileExtension),
-        !empty(album.bannerArtistContribsByRef) && fromRoot.to('media.albumBanner', album.directory, album.bannerFileExtension),
-        !empty(album.wallpaperArtistContribsByRef) && fromRoot.to('media.albumWallpaper', album.directory, album.wallpaperFileExtension),
+        !empty(CacheableObject.getUpdateValue(album, 'bannerArtistContribs')) && fromRoot.to('media.albumBanner', album.directory, album.bannerFileExtension),
+        !empty(CacheableObject.getUpdateValue(album, 'wallpaperArtistContribs')) && fromRoot.to('media.albumWallpaper', album.directory, album.wallpaperFileExtension),
       ])
       .filter(Boolean),
 
@@ -489,22 +678,24 @@ export async function verifyImagePaths(mediaPath, {urls, wikiData}) {
 
   if (empty(missing) && empty(misplaced)) {
     logInfo`All image paths are good - nice! None are missing or misplaced.`;
-    return;
+    return {missing, misplaced};
   }
 
   if (!empty(missing)) {
     logWarn`** Some image files are missing! (${missing.length + ' files'}) **`;
     for (const file of missing) {
-      console.warn(color.yellow(` - `) + file);
+      console.warn(colors.yellow(` - `) + file);
     }
   }
 
   if (!empty(misplaced)) {
     logWarn`** Some image files are misplaced! (${misplaced.length + ' files'}) **`;
     for (const file of misplaced) {
-      console.warn(color.yellow(` - `) + file);
+      console.warn(colors.yellow(` - `) + file);
     }
   }
+
+  return {missing, misplaced};
 }
 
 // Recursively traverses the provided (extant) media path, filtering so only
diff --git a/src/listing-spec.js b/src/listing-spec.js
index 7918dd1e..f57762b0 100644
--- a/src/listing-spec.js
+++ b/src/listing-spec.js
@@ -1,14 +1,4 @@
-import {accumulateSum, empty, showAggregate} from '#sugar';
-
-import {
-  chunkByProperties,
-  getArtistNumContributions,
-  getTotalDuration,
-  sortAlphabetically,
-  sortByDate,
-  sortChronologically,
-  sortFlashesChronologically,
-} from '#wiki-data';
+import {empty, showAggregate} from '#sugar';
 
 const listingSpec = [];
 
diff --git a/src/page/album.js b/src/page/album.js
index 69fcabcf..af410763 100644
--- a/src/page/album.js
+++ b/src/page/album.js
@@ -5,7 +5,6 @@ export function targets({wikiData}) {
 }
 
 export function pathsForTarget(album) {
-  const hasGalleryPage = album.tracks.some(t => t.hasUniqueCoverArt);
   const hasCommentaryPage = !!album.commentary || album.tracks.some(t => t.commentary);
 
   return [
@@ -19,7 +18,7 @@ export function pathsForTarget(album) {
       },
     },
 
-    hasGalleryPage && {
+    {
       type: 'page',
       path: ['albumGallery', album.directory],
 
diff --git a/src/page/artist-alias.js b/src/page/artist-alias.js
index 1da2af41..d2305229 100644
--- a/src/page/artist-alias.js
+++ b/src/page/artist-alias.js
@@ -7,6 +7,12 @@ export function targets({wikiData}) {
 export function pathsForTarget(aliasArtist) {
   const {aliasedArtist} = aliasArtist;
 
+  // Don't generate a redirect page if this aliased name resolves to the same
+  // directory as the original artist! See issue #280.
+  if (aliasArtist.directory === aliasedArtist.directory) {
+    return [];
+  }
+
   return [
     {
       type: 'redirect',
diff --git a/src/page/flash-act.js b/src/page/flash-act.js
new file mode 100644
index 00000000..e54525ae
--- /dev/null
+++ b/src/page/flash-act.js
@@ -0,0 +1,23 @@
+export const description = `flash act gallery pages`;
+
+export function condition({wikiData}) {
+  return wikiData.wikiInfo.enableFlashesAndGames;
+}
+
+export function targets({wikiData}) {
+  return wikiData.flashActData;
+}
+
+export function pathsForTarget(flashAct) {
+  return [
+    {
+      type: 'page',
+      path: ['flashActGallery', flashAct.directory],
+
+      contentFunction: {
+        name: 'generateFlashActGalleryPage',
+        args: [flashAct],
+      },
+    },
+  ];
+}
diff --git a/src/page/flash.js b/src/page/flash.js
index b9d27d0f..7df74158 100644
--- a/src/page/flash.js
+++ b/src/page/flash.js
@@ -1,5 +1,3 @@
-import {empty} from '#sugar';
-
 export const description = `flash & game pages`;
 
 export function condition({wikiData}) {
diff --git a/src/page/index.js b/src/page/index.js
index 48e22d2e..21d93c8f 100644
--- a/src/page/index.js
+++ b/src/page/index.js
@@ -2,6 +2,7 @@ export * as album from './album.js';
 export * as artist from './artist.js';
 export * as artistAlias from './artist-alias.js';
 export * as flash from './flash.js';
+export * as flashAct from './flash-act.js';
 export * as group from './group.js';
 export * as homepage from './homepage.js';
 export * as listing from './listing.js';
diff --git a/src/repl.js b/src/repl.js
index 9ab4ddf0..ead01567 100644
--- a/src/repl.js
+++ b/src/repl.js
@@ -11,7 +11,7 @@ import {generateURLs, urlSpec} from '#urls';
 import {quickLoadAllFromYAML} from '#yaml';
 
 import _find, {bindFind} from '#find';
-import thingConstructors from '#things';
+import thingConstructors, {CacheableObject} from '#things';
 import * as serialize from '#serialize';
 import * as sugar from '#sugar';
 import * as wikiDataUtils from '#wiki-data';
@@ -63,6 +63,7 @@ export async function getContextAssignments({
     WD: wikiData,
 
     ...thingConstructors,
+    CacheableObject,
     language,
 
     ...sugar,
diff --git a/src/static/client2.js b/src/static/client2.js
index 0cdb8b0e..758d91a6 100644
--- a/src/static/client2.js
+++ b/src/static/client2.js
@@ -6,13 +6,28 @@
 // ephemeral nature.
 
 import {getColors} from '../util/colors.js';
-import {getArtistNumContributions} from '../util/wiki-data.js';
+import {empty, stitchArrays} from '../util/sugar.js';
+
+import {
+  filterMultipleArrays,
+  getArtistNumContributions,
+} from '../util/wiki-data.js';
 
 let albumData, artistData;
 let officialAlbumData, fandomAlbumData, beyondAlbumData;
 
 let ready = false;
 
+const clientInfo = window.hsmusicClientInfo = Object.create(null);
+
+const clientSteps = {
+  getPageReferences: [],
+  addInternalListeners: [],
+  mutatePageContent: [],
+  initializeState: [],
+  addPageListeners: [],
+};
+
 // Localiz8tion nonsense ----------------------------------
 
 const language = document.documentElement.getAttribute('lang');
@@ -86,113 +101,148 @@ function fetchData(type, directory) {
 
 // JS-based links -----------------------------------------
 
-for (const a of document.body.querySelectorAll('[data-random]')) {
-  a.addEventListener('click', (evt) => {
-    if (!ready) {
-      evt.preventDefault();
-      return;
-    }
+const scriptedLinkInfo = clientInfo.scriptedLinkInfo = {
+  randomLinks: null,
+  revealLinks: null,
 
-    const tracks = albumData =>
-      albumData
-        .map(album => album.tracks)
-        .reduce((acc, tracks) => acc.concat(tracks), []);
+  nextLink: null,
+  previousLink: null,
+  randomLink: null,
+};
 
-    setTimeout(() => {
-      a.href = rebase('js-disabled');
-    });
+function getScriptedLinkReferences() {
+  scriptedLinkInfo.randomLinks =
+    document.querySelectorAll('[data-random]');
 
-    switch (a.dataset.random) {
-      case 'album':
-        a.href = openAlbum(pick(albumData).directory);
-        break;
-
-      case 'album-in-official':
-        a.href = openAlbum(pick(officialAlbumData).directory);
-        break;
-
-      case 'album-in-fandom':
-        a.href = openAlbum(pick(fandomAlbumData).directory);
-        break;
-
-      case 'album-in-beyond':
-        a.href = openAlbum(pick(beyondAlbumData).directory);
-        break;
-
-      case 'track':
-        a.href = openTrack(getRefDirectory(pick(tracks(albumData))));
-        break;
-
-      case 'track-in-album':
-        a.href = openTrack(getRefDirectory(pick(getAlbum(a).tracks)));
-        break;
-
-      case 'track-in-official':
-        a.href = openTrack(getRefDirectory(pick(tracks(officialAlbumData))));
-        break;
-
-      case 'track-in-fandom':
-        a.href = openTrack(getRefDirectory(pick(tracks(fandomAlbumData))));
-        break;
-
-      case 'track-in-beyond':
-        a.href = openTrack(getRefDirectory(pick(tracks(beyondAlbumData))));
-        break;
-
-      case 'artist':
-        a.href = openArtist(pick(artistData).directory);
-        break;
-
-      case 'artist-more-than-one-contrib':
-        a.href =
-          openArtist(
-            pick(artistData.filter((artist) => getArtistNumContributions(artist) > 1))
-              .directory);
-        break;
-    }
-  });
+  scriptedLinkInfo.revealLinks =
+    document.getElementsByClassName('reveal');
+
+  scriptedLinkInfo.nextNavLink =
+    document.getElementById('next-button');
+
+  scriptedLinkInfo.previousNavLink =
+    document.getElementById('previous-button');
+
+  scriptedLinkInfo.randomNavLink =
+    document.getElementById('random-button');
 }
 
-const next = document.getElementById('next-button');
-const previous = document.getElementById('previous-button');
-const random = document.getElementById('random-button');
+function addRandomLinkListeners() {
+  for (const a of scriptedLinkInfo.randomLinks ?? []) {
+    a.addEventListener('click', evt => {
+      if (!ready) {
+        evt.preventDefault();
+        return;
+      }
+
+      const tracks = albumData =>
+        albumData
+          .map(album => album.tracks)
+          .reduce((acc, tracks) => acc.concat(tracks), []);
 
-const prependTitle = (el, prepend) => {
-  const existing = el.getAttribute('title');
-  if (existing) {
-    el.setAttribute('title', prepend + ' ' + existing);
-  } else {
-    el.setAttribute('title', prepend);
-  }
-};
+      setTimeout(() => {
+        a.href = rebase('js-disabled');
+      });
 
-if (next) prependTitle(next, '(Shift+N)');
-if (previous) prependTitle(previous, '(Shift+P)');
-if (random) prependTitle(random, '(Shift+R)');
-
-document.addEventListener('keypress', (event) => {
-  if (event.shiftKey) {
-    if (event.charCode === 'N'.charCodeAt(0)) {
-      if (next) next.click();
-    } else if (event.charCode === 'P'.charCodeAt(0)) {
-      if (previous) previous.click();
-    } else if (event.charCode === 'R'.charCodeAt(0)) {
-      if (random && ready) random.click();
-    }
+      switch (a.dataset.random) {
+        case 'album':
+          a.href = openAlbum(pick(albumData).directory);
+          break;
+
+        case 'album-in-official':
+          a.href = openAlbum(pick(officialAlbumData).directory);
+          break;
+
+        case 'album-in-fandom':
+          a.href = openAlbum(pick(fandomAlbumData).directory);
+          break;
+
+        case 'album-in-beyond':
+          a.href = openAlbum(pick(beyondAlbumData).directory);
+          break;
+
+        case 'track':
+          a.href = openTrack(getRefDirectory(pick(tracks(albumData))));
+          break;
+
+        case 'track-in-album':
+          a.href = openTrack(getRefDirectory(pick(getAlbum(a).tracks)));
+          break;
+
+        case 'track-in-official':
+          a.href = openTrack(getRefDirectory(pick(tracks(officialAlbumData))));
+          break;
+
+        case 'track-in-fandom':
+          a.href = openTrack(getRefDirectory(pick(tracks(fandomAlbumData))));
+          break;
+
+        case 'track-in-beyond':
+          a.href = openTrack(getRefDirectory(pick(tracks(beyondAlbumData))));
+          break;
+
+        case 'artist':
+          a.href = openArtist(pick(artistData).directory);
+          break;
+
+        case 'artist-more-than-one-contrib':
+          a.href =
+            openArtist(
+              pick(artistData.filter((artist) => getArtistNumContributions(artist) > 1))
+                .directory);
+          break;
+      }
+    });
   }
-});
+}
 
-for (const reveal of document.querySelectorAll('.reveal')) {
-  reveal.addEventListener('click', (event) => {
-    if (!reveal.classList.contains('revealed')) {
-      reveal.classList.add('revealed');
-      event.preventDefault();
-      event.stopPropagation();
-      reveal.dispatchEvent(new CustomEvent('hsmusic-reveal'));
+function mutateNavigationLinkContent() {
+  const prependTitle = (el, prepend) =>
+    el?.setAttribute('title',
+      (el.hasAttribute('title')
+        ? prepend + ' ' + el.getAttribute('title')
+        : prepend));
+
+  prependTitle(scriptedLinkInfo.nextNavLink, '(Shift+N)');
+  prependTitle(scriptedLinkInfo.previousNavLink, '(Shift+P)');
+  prependTitle(scriptedLinkInfo.randomNavLink, '(Shift+R)');
+}
+
+function addNavigationKeyPressListeners() {
+  document.addEventListener('keypress', (event) => {
+    if (event.shiftKey) {
+      if (event.charCode === 'N'.charCodeAt(0)) {
+        scriptedLinkInfo.nextNavLink?.click();
+      } else if (event.charCode === 'P'.charCodeAt(0)) {
+        scriptedLinkInfo.previousNavLink?.click();
+      } else if (event.charCode === 'R'.charCodeAt(0)) {
+        if (ready) {
+          scriptedLinkInfo.randomNavLink?.click();
+        }
+      }
     }
   });
 }
 
+function addRevealLinkClickListeners() {
+  for (const reveal of scriptedLinkInfo.revealLinks ?? []) {
+    reveal.addEventListener('click', (event) => {
+      if (!reveal.classList.contains('revealed')) {
+        reveal.classList.add('revealed');
+        event.preventDefault();
+        event.stopPropagation();
+        reveal.dispatchEvent(new CustomEvent('hsmusic-reveal'));
+      }
+    });
+  }
+}
+
+clientSteps.getPageReferences.push(getScriptedLinkReferences);
+clientSteps.addPageListeners.push(addRandomLinkListeners);
+clientSteps.addPageListeners.push(addNavigationKeyPressListeners);
+clientSteps.addPageListeners.push(addRevealLinkClickListeners);
+clientSteps.mutatePageContent.push(mutateNavigationLinkContent);
+
 const elements1 = document.getElementsByClassName('js-hide-once-data');
 const elements2 = document.getElementsByClassName('js-show-once-data');
 
@@ -454,199 +504,393 @@ if (localStorage.tryInfoCards) {
 
 // Custom hash links --------------------------------------
 
-function addHashLinkHandlers() {
+const hashLinkInfo = clientInfo.hashLinkInfo = {
+  links: null,
+  hrefs: null,
+  targets: null,
+
+  state: {
+    highlightedTarget: null,
+    scrollingAfterClick: false,
+    concludeScrollingStateInterval: null,
+  },
+
+  event: {
+    whenHashLinkClicked: [],
+  },
+};
+
+function getHashLinkReferences() {
+  const info = hashLinkInfo;
+
+  info.links =
+    Array.from(document.querySelectorAll('a[href^="#"]:not([href="#"])'));
+
+  info.hrefs =
+    info.links
+      .map(link => link.getAttribute('href'));
+
+  info.targets =
+    info.hrefs
+      .map(href => document.getElementById(href.slice(1)));
+
+  filterMultipleArrays(
+    info.links,
+    info.hrefs,
+    info.targets,
+    (_link, _href, target) => target);
+}
+
+function processScrollingAfterHashLinkClicked() {
+  const {state} = hashLinkInfo;
+
+  if (state.concludeScrollingStateInterval) return;
+
+  let lastScroll = window.scrollY;
+  state.scrollingAfterClick = true;
+  state.concludeScrollingStateInterval = setInterval(() => {
+    if (Math.abs(window.scrollY - lastScroll) < 10) {
+      clearInterval(state.concludeScrollingStateInterval);
+      state.scrollingAfterClick = false;
+      state.concludeScrollingStateInterval = null;
+    } else {
+      lastScroll = window.scrollY;
+    }
+  }, 200);
+}
+
+function addHashLinkListeners() {
   // Instead of defining a scroll offset (to account for the sticky heading)
   // in JavaScript, we interface with the CSS property 'scroll-margin-top'.
   // This lets the scroll offset be consolidated where it makes sense, and
   // sets an appropriate offset when (re)loading a page with hash for free!
 
-  let wasHighlighted;
-
-  for (const a of document.links) {
-    const href = a.getAttribute('href');
-    if (!href || !href.startsWith('#')) {
-      continue;
-    }
+  const info = hashLinkInfo;
+  const {state, event} = info;
 
-    a.addEventListener('click', handleHashLinkClicked);
-  }
+  for (const {hashLink, href, target} of stitchArrays({
+    hashLink: info.links,
+    href: info.hrefs,
+    target: info.targets,
+  })) {
+    hashLink.addEventListener('click', evt => {
+      if (evt.metaKey || evt.shiftKey || evt.ctrlKey || evt.altKey) {
+        return;
+      }
 
-  function handleHashLinkClicked(evt) {
-    if (evt.metaKey || evt.shiftKey || evt.ctrlKey || evt.altKey) {
-      return;
-    }
+      // Hide skipper box right away, so the layout is updated on time for the
+      // math operations coming up next.
+      const skipper = document.getElementById('skippers');
+      skipper.style.display = 'none';
+      setTimeout(() => skipper.style.display = '');
 
-    const href = evt.target.getAttribute('href');
-    const id = href.slice(1);
-    const linked = document.getElementById(id);
+      const box = target.getBoundingClientRect();
+      const style = window.getComputedStyle(target);
 
-    if (!linked) {
-      return;
-    }
+      const scrollY =
+          window.scrollY
+        + box.top
+        - style['scroll-margin-top'].replace('px', '');
 
-    // Hide skipper box right away, so the layout is updated on time for the
-    // math operations coming up next.
-    const skipper = document.getElementById('skippers');
-    skipper.style.display = 'none';
-    setTimeout(() => skipper.style.display = '');
+      evt.preventDefault();
+      history.pushState({}, '', href);
+      window.scrollTo({top: scrollY, behavior: 'smooth'});
+      target.focus({preventScroll: true});
 
-    const box = linked.getBoundingClientRect();
-    const style = window.getComputedStyle(linked);
+      const maxScroll =
+          document.body.scrollHeight
+        - window.innerHeight;
 
-    const scrollY =
-        window.scrollY
-      + box.top
-      - style['scroll-margin-top'].replace('px', '');
+      if (scrollY > maxScroll && target.classList.contains('content-heading')) {
+        if (state.highlightedTarget) {
+          state.highlightedTarget.classList.remove('highlight-hash-link');
+        }
 
-    evt.preventDefault();
-    history.pushState({}, '', href);
-    window.scrollTo({top: scrollY, behavior: 'smooth'});
-    linked.focus({preventScroll: true});
+        target.classList.add('highlight-hash-link');
+        state.highlightedTarget = target;
+      }
 
-    const maxScroll =
-        document.body.scrollHeight
-      - window.innerHeight;
+      processScrollingAfterHashLinkClicked();
 
-    if (scrollY > maxScroll && linked.classList.contains('content-heading')) {
-      if (wasHighlighted) {
-        wasHighlighted.classList.remove('highlight-hash-link');
+      for (const handler of event.whenHashLinkClicked) {
+        handler({
+          link: hashLink,
+        });
       }
+    });
+  }
 
-      wasHighlighted = linked;
-      linked.classList.add('highlight-hash-link');
-      linked.addEventListener('animationend', function handle(evt) {
-        if (evt.animationName === 'highlight-hash-link') {
-          linked.removeEventListener('animationend', handle);
-          linked.classList.remove('highlight-hash-link');
-          wasHighlighted = null;
-        }
-      });
-    }
+  for (const target of info.targets) {
+    target.addEventListener('animationend', evt => {
+      if (evt.animationName !== 'highlight-hash-link') return;
+      target.classList.remove('highlight-hash-link');
+      if (target !== state.highlightedTarget) return;
+      state.highlightedTarget = null;
+    });
   }
 }
 
-addHashLinkHandlers();
+clientSteps.getPageReferences.push(getHashLinkReferences);
+clientSteps.addPageListeners.push(addHashLinkListeners);
 
 // Sticky content heading ---------------------------------
 
-const stickyHeadingInfo = Array.from(document.querySelectorAll('.content-sticky-heading-container'))
-  .map(stickyContainer => {
-    const {parentElement: contentContainer} = stickyContainer;
-    const stickySubheadingRow = stickyContainer.querySelector('.content-sticky-subheading-row');
-    const stickySubheading = stickySubheadingRow.querySelector('h2');
-    const stickyCoverContainer = stickyContainer.querySelector('.content-sticky-heading-cover-container');
-    const stickyCover = stickyCoverContainer?.querySelector('.content-sticky-heading-cover');
-    const contentHeadings = Array.from(contentContainer.querySelectorAll('.content-heading'));
-    const contentCover = contentContainer.querySelector('#cover-art-container');
-
-    return {
-      contentContainer,
-      contentCover,
-      contentHeadings,
-      stickyContainer,
-      stickyCover,
-      stickyCoverContainer,
-      stickySubheading,
-      stickySubheadingRow,
-      state: {
-        displayedHeading: null,
-      },
-    };
-  });
+const stickyHeadingInfo = clientInfo.stickyHeadingInfo = {
+  stickyContainers: null,
 
-const topOfViewInside = (el, scroll = window.scrollY) => (
-  scroll > el.offsetTop &&
-  scroll < el.offsetTop + el.offsetHeight
-);
-
-function prepareStickyHeadings() {
-  for (const {
-    contentCover,
-    stickyCover,
-  } of stickyHeadingInfo) {
-    const coverRevealImage = contentCover?.querySelector('.reveal');
-    if (coverRevealImage) {
-      stickyCover.classList.add('content-sticky-heading-cover-needs-reveal');
-      coverRevealImage.addEventListener('hsmusic-reveal', () => {
-        stickyCover.classList.remove('content-sticky-heading-cover-needs-reveal');
-      });
+  stickySubheadingRows: null,
+  stickySubheadings: null,
+
+  stickyCoverContainers: null,
+  stickyCoverTextAreas: null,
+  stickyCovers: null,
+
+  contentContainers: null,
+  contentHeadings: null,
+  contentCovers: null,
+  contentCoversReveal: null,
+
+  state: {
+    displayedHeading: null,
+  },
+
+  event: {
+    whenDisplayedHeadingChanges: [],
+  },
+};
+
+function getStickyHeadingReferences() {
+  const info = stickyHeadingInfo;
+
+  info.stickyContainers =
+    Array.from(document.getElementsByClassName('content-sticky-heading-container'));
+
+  info.stickyCoverContainers =
+    info.stickyContainers
+      .map(el => el.querySelector('.content-sticky-heading-cover-container'));
+
+  info.stickyCovers =
+    info.stickyCoverContainers
+      .map(el => el?.querySelector('.content-sticky-heading-cover'));
+
+  info.stickyCoverTextAreas =
+    info.stickyCovers
+      .map(el => el?.querySelector('.image-text-area'));
+
+  info.stickySubheadingRows =
+    info.stickyContainers
+      .map(el => el.querySelector('.content-sticky-subheading-row'));
+
+  info.stickySubheadings =
+    info.stickySubheadingRows
+      .map(el => el.querySelector('h2'));
+
+  info.contentContainers =
+    info.stickyContainers
+      .map(el => el.parentElement);
+
+  info.contentCovers =
+    info.contentContainers
+      .map(el => el.querySelector('#cover-art-container'));
+
+  info.contentCoversReveal =
+    info.contentCovers
+      .map(el => el ? !!el.querySelector('.reveal') : null);
+
+  info.contentHeadings =
+    info.contentContainers
+      .map(el => Array.from(el.querySelectorAll('.content-heading')));
+}
+
+function removeTextPlaceholderStickyHeadingCovers() {
+  const info = stickyHeadingInfo;
+
+  const hasTextArea =
+    info.stickyCoverTextAreas.map(el => !!el);
+
+  const coverContainersWithTextArea =
+    info.stickyCoverContainers
+      .filter((_el, index) => hasTextArea[index]);
+
+  for (const el of coverContainersWithTextArea) {
+    el.remove();
+  }
+
+  info.stickyCoverContainers =
+    info.stickyCoverContainers
+      .map((el, index) => hasTextArea[index] ? null : el);
+
+  info.stickyCovers =
+    info.stickyCovers
+      .map((el, index) => hasTextArea[index] ? null : el);
+
+  info.stickyCoverTextAreas =
+    info.stickyCoverTextAreas
+      .slice()
+      .fill(null);
+}
+
+function addRevealClassToStickyHeadingCovers() {
+  const info = stickyHeadingInfo;
+
+  const stickyCoversWhichReveal =
+    info.stickyCovers
+      .filter((_el, index) => info.contentCoversReveal[index]);
+
+  for (const el of stickyCoversWhichReveal) {
+    el.classList.add('content-sticky-heading-cover-needs-reveal');
+  }
+}
+
+function addRevealListenersForStickyHeadingCovers() {
+  const info = stickyHeadingInfo;
+
+  const stickyCovers = info.stickyCovers.slice();
+  const contentCovers = info.contentCovers.slice();
+
+  filterMultipleArrays(
+    stickyCovers,
+    contentCovers,
+    (_stickyCover, _contentCover, index) => info.contentCoversReveal[index]);
+
+  for (const {stickyCover, contentCover} of stitchArrays({
+    stickyCover: stickyCovers,
+    contentCover: contentCovers,
+  })) {
+    // TODO: Janky - should use internal event instead of DOM event
+    contentCover.querySelector('.reveal').addEventListener('hsmusic-reveal', () => {
+      stickyCover.classList.remove('content-sticky-heading-cover-needs-reveal');
+    });
+  }
+}
+
+function topOfViewInside(el, scroll = window.scrollY) {
+  return (
+    scroll > el.offsetTop &&
+    scroll < el.offsetTop + el.offsetHeight);
+}
+
+function updateStickyCoverVisibility(index) {
+  const info = stickyHeadingInfo;
+
+  const stickyCoverContainer = info.stickyCoverContainers[index];
+  const contentCover = info.contentCovers[index];
+
+  if (contentCover && stickyCoverContainer) {
+    if (contentCover.getBoundingClientRect().bottom < 0) {
+      stickyCoverContainer.classList.add('visible');
+    } else {
+      stickyCoverContainer.classList.remove('visible');
     }
   }
 }
 
-function updateStickyHeading() {
-  for (const {
-    contentContainer,
-    contentCover,
-    contentHeadings,
-    stickyContainer,
-    stickyCoverContainer,
-    stickySubheading,
-    stickySubheadingRow,
-    state,
-  } of stickyHeadingInfo) {
-    let closestHeading = null;
+function getContentHeadingClosestToStickySubheading(index) {
+  const info = stickyHeadingInfo;
 
-    if (contentCover && stickyCoverContainer) {
-      if (contentCover.getBoundingClientRect().bottom < 0) {
-        stickyCoverContainer.classList.add('visible');
-      } else {
-        stickyCoverContainer.classList.remove('visible');
-      }
+  const contentContainer = info.contentContainers[index];
+
+  if (!topOfViewInside(contentContainer)) {
+    return null;
+  }
+
+  const stickySubheading = info.stickySubheadings[index];
+
+  if (stickySubheading.childNodes.length === 0) {
+    // Supply a non-breaking space to ensure correct basic line height.
+    stickySubheading.appendChild(document.createTextNode('\xA0'));
+  }
+
+  const stickyContainer = info.stickyContainers[index];
+  const stickyRect = stickyContainer.getBoundingClientRect();
+
+  // TODO: Should this compute with the subheading row instead of h2?
+  const subheadingRect = stickySubheading.getBoundingClientRect();
+
+  const stickyBottom = stickyRect.bottom + subheadingRect.height;
+
+  // Iterate from bottom to top of the content area.
+  const contentHeadings = info.contentHeadings[index];
+  for (const heading of contentHeadings.slice().reverse()) {
+    const headingRect = heading.getBoundingClientRect();
+    if (headingRect.y + headingRect.height / 1.5 < stickyBottom + 20) {
+      return heading;
     }
+  }
 
-    if (topOfViewInside(contentContainer)) {
-      if (stickySubheading.childNodes.length === 0) {
-        // &nbsp; to ensure correct basic line height
-        stickySubheading.appendChild(document.createTextNode('\xA0'));
-      }
+  return null;
+}
 
-      const stickyRect = stickyContainer.getBoundingClientRect();
-      const subheadingRect = stickySubheading.getBoundingClientRect();
-      const stickyBottom = stickyRect.bottom + subheadingRect.height;
-
-      // This array is reversed so that we're starting from the bottom when
-      // iterating over it.
-      for (let i = contentHeadings.length - 1; i >= 0; i--) {
-        const heading = contentHeadings[i];
-        const headingRect = heading.getBoundingClientRect();
-        if (headingRect.y + headingRect.height / 1.5 < stickyBottom + 20) {
-          closestHeading = heading;
-          break;
+function updateStickySubheadingContent(index) {
+  const info = stickyHeadingInfo;
+  const {event, state} = info;
+
+  const closestHeading = getContentHeadingClosestToStickySubheading(index);
+
+  if (state.displayedHeading === closestHeading) return;
+
+  const stickySubheadingRow = info.stickySubheadingRows[index];
+
+  if (closestHeading) {
+    const stickySubheading = info.stickySubheadings[index];
+
+    // Array.from needed to iterate over a live array with for..of
+    for (const child of Array.from(stickySubheading.childNodes)) {
+      child.remove();
+    }
+
+    for (const child of closestHeading.childNodes) {
+      if (child.tagName === 'A') {
+        for (const grandchild of child.childNodes) {
+          stickySubheading.appendChild(grandchild.cloneNode(true));
         }
+      } else {
+        stickySubheading.appendChild(child.cloneNode(true));
       }
     }
 
-    if (state.displayedHeading !== closestHeading) {
-      if (closestHeading) {
-        // Array.from needed to iterate over a live array with for..of
-        for (const child of Array.from(stickySubheading.childNodes)) {
-          child.remove();
-        }
+    stickySubheadingRow.classList.add('visible');
+  } else {
+    stickySubheadingRow.classList.remove('visible');
+  }
 
-        for (const child of closestHeading.childNodes) {
-          if (child.tagName === 'A') {
-            for (const grandchild of child.childNodes) {
-              stickySubheading.appendChild(grandchild.cloneNode(true));
-            }
-          } else {
-            stickySubheading.appendChild(child.cloneNode(true));
-          }
-        }
+  const oldDisplayedHeading = state.displayedHeading;
 
-        stickySubheadingRow.classList.add('visible');
-      } else {
-        stickySubheadingRow.classList.remove('visible');
-      }
+  state.displayedHeading = closestHeading;
 
-      state.displayedHeading = closestHeading;
-    }
+  for (const handler of event.whenDisplayedHeadingChanges) {
+    handler(index, {
+      oldHeading: oldDisplayedHeading,
+      newHeading: closestHeading,
+    });
   }
 }
 
-document.addEventListener('scroll', updateStickyHeading);
-prepareStickyHeadings();
-updateStickyHeading();
+function updateStickyHeadings(index) {
+  updateStickyCoverVisibility(index);
+  updateStickySubheadingContent(index);
+}
+
+function initializeStateForStickyHeadings() {
+  for (let i = 0; i < stickyHeadingInfo.stickyContainers.length; i++) {
+    updateStickyHeadings(i);
+  }
+}
+
+function addScrollListenerForStickyHeadings() {
+  document.addEventListener('scroll', () => {
+    for (let i = 0; i < stickyHeadingInfo.stickyContainers.length; i++) {
+      updateStickyHeadings(i);
+    }
+  });
+}
+
+clientSteps.getPageReferences.push(getStickyHeadingReferences);
+clientSteps.mutatePageContent.push(removeTextPlaceholderStickyHeadingCovers);
+clientSteps.mutatePageContent.push(addRevealClassToStickyHeadingCovers);
+clientSteps.initializeState.push(initializeStateForStickyHeadings);
+clientSteps.addPageListeners.push(addRevealListenersForStickyHeadingCovers);
+clientSteps.addPageListeners.push(addScrollListenerForStickyHeadings);
 
 // Image overlay ------------------------------------------
 
@@ -709,24 +953,48 @@ function handleImageLinkClicked(evt) {
   const mainImage = document.getElementById('image-overlay-image');
   const thumbImage = document.getElementById('image-overlay-image-thumb');
 
-  const mainThumbSize = getPreferredThumbSize();
-
-  const source = evt.target.closest('a').href;
+  const {href: originalSrc} = evt.target.closest('a');
+  const {dataset: {
+    originalSize: originalFileSize,
+    thumbs: availableThumbList,
+  }} = evt.target.closest('a').querySelector('img');
+
+  updateFileSizeInformation(originalFileSize);
+
+  let mainSrc = null;
+  let thumbSrc = null;
+
+  if (availableThumbList) {
+    const {thumb: mainThumb, length: mainLength} = getPreferredThumbSize(availableThumbList);
+    const {thumb: smallThumb, length: smallLength} = getSmallestThumbSize(availableThumbList);
+    mainSrc = originalSrc.replace(/\.(jpg|png)$/, `.${mainThumb}.jpg`);
+    thumbSrc = originalSrc.replace(/\.(jpg|png)$/, `.${smallThumb}.jpg`);
+    // Show the thumbnail size on each <img> element's data attributes.
+    // Y'know, just for debugging convenience.
+    mainImage.dataset.displayingThumb = `${mainThumb}:${mainLength}`;
+    thumbImage.dataset.displayingThumb = `${smallThumb}:${smallLength}`;
+  } else {
+    mainSrc = originalSrc;
+    thumbSrc = null;
+    mainImage.dataset.displayingThumb = '';
+    thumbImage.dataset.displayingThumb = '';
+  }
 
-  const mainSrc = source.replace(/\.(jpg|png)$/, `.${mainThumbSize}.jpg`);
-  const thumbSrc = source.replace(/\.(jpg|png)$/, '.small.jpg');
+  if (thumbSrc) {
+    thumbImage.src = thumbSrc;
+    thumbImage.style.display = null;
+  } else {
+    thumbImage.src = '';
+    thumbImage.style.display = 'none';
+  }
 
-  thumbImage.src = thumbSrc;
   for (const viewOriginal of allViewOriginal) {
-    viewOriginal.href = source;
+    viewOriginal.href = originalSrc;
   }
 
   mainImage.addEventListener('load', handleMainImageLoaded);
   mainImage.addEventListener('error', handleMainImageErrored);
 
-  const fileSize = evt.target.closest('a').querySelector('img').dataset.originalSize;
-  updateFileSizeInformation(fileSize);
-
   container.style.setProperty('--download-progress', '0%');
   loadImage(mainSrc, progress => {
     container.style.setProperty('--download-progress', (20 + 0.8 * progress) + '%');
@@ -750,7 +1018,21 @@ function handleImageLinkClicked(evt) {
   }
 }
 
-function getPreferredThumbSize() {
+function parseThumbList(availableThumbList) {
+  // Parse all the available thumbnail sizes! These are provided by the actual
+  // content generation on each image.
+  const defaultThumbList = 'huge:1400 semihuge:1200 large:800 medium:400 small:250'
+  const availableSizes =
+    (availableThumbList || defaultThumbList)
+      .split(' ')
+      .map(part => part.split(':'))
+      .map(([thumb, length]) => ({thumb, length: parseInt(length)}))
+      .sort((a, b) => a.length - b.length);
+
+  return availableSizes;
+}
+
+function getPreferredThumbSize(availableThumbList) {
   // Assuming a square, the image will be constrained to the lesser window
   // dimension. Coefficient here matches CSS dimensions for image overlay.
   const constrainedLength = Math.floor(Math.min(
@@ -761,17 +1043,30 @@ function getPreferredThumbSize() {
   // device configurations.
   const visualLength = window.devicePixelRatio * constrainedLength;
 
-  const largeLength = 800;
-  const semihugeLength = 1200;
+  const availableSizes = parseThumbList(availableThumbList);
+
+  // Starting from the smallest dimensions, find (and return) the first
+  // available length which hits a "good enough" threshold - it's got to be
+  // at least that percent of the way to the actual displayed dimensions.
   const goodEnoughThreshold = 0.90;
 
-  if (Math.floor(visualLength * goodEnoughThreshold) <= largeLength) {
-    return 'large';
-  } else if (Math.floor(visualLength * goodEnoughThreshold) <= semihugeLength) {
-    return 'semihuge';
-  } else {
-    return 'huge';
+  // (The last item is skipped since we'd be falling back to it anyway.)
+  for (const {thumb, length} of availableSizes.slice(0, -1)) {
+    if (Math.floor(visualLength * goodEnoughThreshold) <= length) {
+      return {thumb, length};
+    }
   }
+
+  // If none of the items in the list were big enough to hit the "good enough"
+  // threshold, just use the largest size available.
+  return availableSizes[availableSizes.length - 1];
+}
+
+function getSmallestThumbSize(availableThumbList) {
+  // Just snag the smallest size. This'll be used for displaying the "preview"
+  // as the bigger one is loading.
+  const availableSizes = parseThumbList(availableThumbList);
+  return availableSizes[0];
 }
 
 function updateFileSizeInformation(fileSize) {
@@ -913,3 +1208,227 @@ for (const info of groupContributionsTableInfo) {
     sortGroupContributionsTableBy(info, 'count');
   });
 }
+
+// Sticky commentary sidebar ------------------------------
+
+const albumCommentarySidebarInfo = clientInfo.albumCommentarySidebarInfo = {
+  sidebar: null,
+
+  sidebarTrackLinks: null,
+  sidebarTrackDirectories: null,
+
+  sidebarTrackSections: null,
+  sidebarTrackSectionStartIndices: null,
+
+  state: {
+    currentTrackSection: null,
+    currentTrackLink: null,
+    justChangedTrackSection: false,
+  },
+};
+
+function getAlbumCommentarySidebarReferences() {
+  const info = albumCommentarySidebarInfo;
+
+  info.sidebar =
+    document.getElementById('sidebar-left');
+
+  info.sidebarHeading =
+    info.sidebar.querySelector('h1');
+
+  info.sidebarTrackLinks =
+    Array.from(info.sidebar.querySelectorAll('li a'));
+
+  info.sidebarTrackDirectories =
+    info.sidebarTrackLinks
+      .map(el => el.getAttribute('href')?.slice(1) ?? null);
+
+  info.sidebarTrackSections =
+    Array.from(info.sidebar.getElementsByTagName('details'));
+
+  info.sidebarTrackSectionStartIndices =
+    info.sidebarTrackSections
+      .map(details => details.querySelector('ol, ul'))
+      .reduce(
+        (accumulator, _list, index, array) =>
+          (empty(accumulator)
+            ? [0]
+            : [
+              ...accumulator,
+              (accumulator[accumulator.length - 1] +
+                array[index - 1].querySelectorAll('li a').length),
+            ]),
+        []);
+}
+
+function scrollAlbumCommentarySidebar() {
+  const info = albumCommentarySidebarInfo;
+  const {state} = info;
+  const {currentTrackLink, currentTrackSection} = state;
+
+  if (!currentTrackLink) {
+    return;
+  }
+
+  const {sidebar, sidebarHeading} = info;
+
+  const scrollTop = sidebar.scrollTop;
+
+  const headingRect = sidebarHeading.getBoundingClientRect();
+  const sidebarRect = sidebar.getBoundingClientRect();
+
+  const stickyPadding = headingRect.height;
+  const sidebarViewportHeight = sidebarRect.height - stickyPadding;
+
+  const linkRect = currentTrackLink.getBoundingClientRect();
+  const sectionRect = currentTrackSection.getBoundingClientRect();
+
+  const sectionTopEdge =
+    sectionRect.top - (sidebarRect.top - scrollTop);
+
+  const sectionHeight =
+    sectionRect.height;
+
+  const sectionScrollTop =
+    sectionTopEdge - stickyPadding - 10;
+
+  const linkTopEdge =
+    linkRect.top - (sidebarRect.top - scrollTop);
+
+  const linkBottomEdge =
+    linkRect.bottom - (sidebarRect.top - scrollTop);
+
+  const linkScrollTop =
+    linkTopEdge - stickyPadding - 5;
+
+  const linkDistanceFromSection =
+    linkScrollTop - sectionTopEdge;
+
+  const linkVisibleFromTopOfSection =
+    linkBottomEdge - sectionTopEdge > sidebarViewportHeight;
+
+  const linkScrollBottom =
+    linkScrollTop - sidebarViewportHeight + linkRect.height + 20;
+
+  const maxScrollInViewport =
+    scrollTop + stickyPadding + sidebarViewportHeight;
+
+  const minScrollInViewport =
+    scrollTop + stickyPadding;
+
+  if (linkBottomEdge > maxScrollInViewport) {
+    if (linkVisibleFromTopOfSection) {
+      sidebar.scrollTo({top: linkScrollBottom, behavior: 'smooth'});
+    } else {
+      sidebar.scrollTo({top: sectionScrollTop, behavior: 'smooth'});
+    }
+  } else if (linkTopEdge < minScrollInViewport) {
+    if (linkVisibleFromTopOfSection) {
+      sidebar.scrollTo({top: linkScrollTop, behavior: 'smooth'});
+    } else {
+      sidebar.scrollTo({top: sectionScrollTop, behavior: 'smooth'});
+    }
+  } else if (state.justChangedTrackSection) {
+    if (sectionHeight < sidebarViewportHeight) {
+      sidebar.scrollTo({top: sectionScrollTop, behavior: 'smooth'});
+    }
+  }
+}
+
+function markDirectoryAsCurrentForAlbumCommentary(trackDirectory) {
+  const info = albumCommentarySidebarInfo;
+  const {state} = info;
+
+  const trackIndex =
+    (trackDirectory
+      ? info.sidebarTrackDirectories
+          .indexOf(trackDirectory)
+      : -1);
+
+  const sectionIndex =
+    (trackIndex >= 0
+      ? info.sidebarTrackSectionStartIndices
+          .findIndex((start, index, array) =>
+            (index === array.length - 1
+              ? true
+              : trackIndex < array[index + 1]))
+      : -1);
+
+  const sidebarTrackLink =
+    (trackIndex >= 0
+      ? info.sidebarTrackLinks[trackIndex]
+      : null);
+
+  const sidebarTrackSection =
+    (sectionIndex >= 0
+      ? info.sidebarTrackSections[sectionIndex]
+      : null);
+
+  state.currentTrackLink?.classList?.remove('current');
+  state.currentTrackLink = sidebarTrackLink;
+  state.currentTrackLink?.classList?.add('current');
+
+  if (sidebarTrackSection !== state.currentTrackSection) {
+    if (sidebarTrackSection && !sidebarTrackSection.open) {
+      if (state.currentTrackSection) {
+        state.currentTrackSection.open = false;
+      }
+
+      sidebarTrackSection.open = true;
+    }
+
+    state.currentTrackSection?.classList?.remove('current');
+    state.currentTrackSection = sidebarTrackSection;
+    state.currentTrackSection?.classList?.add('current');
+    state.justChangedTrackSection = true;
+  } else {
+    state.justChangedTrackSection = false;
+  }
+}
+
+function addAlbumCommentaryInternalListeners() {
+  const info = albumCommentarySidebarInfo;
+
+  const mainContentIndex =
+    (stickyHeadingInfo.contentContainers ?? [])
+      .findIndex(({id}) => id === 'content');
+
+  if (mainContentIndex === -1) return;
+
+  stickyHeadingInfo.event.whenDisplayedHeadingChanges.push((index, {newHeading}) => {
+    if (index !== mainContentIndex) return;
+    if (hashLinkInfo.state.scrollingAfterClick) return;
+
+    const trackDirectory =
+      (newHeading
+        ? newHeading.id
+        : null);
+
+    markDirectoryAsCurrentForAlbumCommentary(trackDirectory);
+    scrollAlbumCommentarySidebar();
+  });
+
+  hashLinkInfo.event.whenHashLinkClicked.push(({link}) => {
+    const hash = link.getAttribute('href').slice(1);
+    if (!info.sidebarTrackDirectories.includes(hash)) return;
+    markDirectoryAsCurrentForAlbumCommentary(hash);
+  });
+}
+
+if (document.documentElement.dataset.urlKey === 'localized.albumCommentary') {
+  clientSteps.getPageReferences.push(getAlbumCommentarySidebarReferences);
+  clientSteps.addInternalListeners.push(addAlbumCommentaryInternalListeners);
+}
+
+// Run setup steps ----------------------------------------
+
+for (const [key, steps] of Object.entries(clientSteps)) {
+  for (const step of steps) {
+    try {
+      step();
+    } catch (error) {
+      console.warn(`During ${key}, failed to run ${step.name}`);
+      console.debug(error);
+    }
+  }
+}
diff --git a/src/static/site4.css b/src/static/site5.css
index f79c0c2d..0eb7dcda 100644
--- a/src/static/site4.css
+++ b/src/static/site5.css
@@ -285,6 +285,8 @@ body::before {
 .sidebar > h3,
 .sidebar > p {
   text-align: center;
+  padding-left: 4px;
+  padding-right: 4px;
 }
 
 .sidebar h1 {
@@ -437,6 +439,14 @@ a.current {
   font-weight: 800;
 }
 
+a:not([href]) {
+  cursor: default;
+}
+
+a:not([href]):hover {
+  text-decoration: none;
+}
+
 .nav-main-links > span > span {
   white-space: nowrap;
 }
@@ -533,6 +543,13 @@ p .current {
   margin-top: 5px;
 }
 
+.commentary-art {
+  float: right;
+  width: 30%;
+  max-width: 250px;
+  margin: 15px 0 10px 20px;
+}
+
 .js-hide,
 .js-show-once-data,
 .js-hide-once-data {
@@ -558,7 +575,7 @@ a.box img {
   height: auto;
 }
 
-a.box .square .image-container {
+.square .image-container {
   width: 100%;
   height: 100%;
 }
@@ -680,10 +697,14 @@ p code {
   margin-bottom: 0;
 }
 
+main.long-content {
+  --long-content-padding-ratio: 0.12;
+}
+
 main.long-content .main-content-container,
 main.long-content > h1 {
-  padding-left: 12%;
-  padding-right: 12%;
+  padding-left: calc(var(--long-content-padding-ratio) * 100%);
+  padding-right: calc(var(--long-content-padding-ratio) * 100%);
 }
 
 dl dt {
@@ -773,6 +794,10 @@ li > ul {
   display: none;
 }
 
+html[data-url-key="localized.albumCommentary"] li.no-commentary {
+  opacity: 0.7;
+}
+
 /* Images */
 
 .image-container {
@@ -1250,6 +1275,10 @@ html[data-url-key="localized.home"] .carousel-container {
   animation-delay: 125ms;
 }
 
+h3.content-heading {
+  clear: both;
+}
+
 /* This animation's name is referenced in JavaScript */
 @keyframes highlight-hash-link {
   0% {
@@ -1298,8 +1327,8 @@ main.long-content .content-sticky-heading-container {
 
 main.long-content .content-sticky-heading-container .content-sticky-heading-row,
 main.long-content .content-sticky-heading-container .content-sticky-subheading-row {
-  padding-left: calc(0.12 * (100% - 2 * var(--content-padding)) + var(--content-padding));
-  padding-right: calc(0.12 * (100% - 2 * var(--content-padding)) + var(--content-padding));
+  padding-left: calc(var(--long-content-padding-ratio) * (100% - 2 * var(--content-padding)) + var(--content-padding));
+  padding-right: calc(var(--long-content-padding-ratio) * (100% - 2 * var(--content-padding)) + var(--content-padding));
 }
 
 .content-sticky-heading-row {
@@ -1438,6 +1467,45 @@ main.long-content .content-sticky-heading-container .content-sticky-subheading-r
   align-self: flex-start;
 }
 
+.sidebar-column.sidebar.sticky-column {
+  max-height: calc(100vh - 20px);
+  align-self: start;
+  padding-bottom: 0;
+  box-sizing: border-box;
+  flex-basis: 275px;
+  padding-top: 0;
+  overflow-y: scroll;
+  scrollbar-width: thin;
+  scrollbar-color: var(--dark-color);
+}
+
+.sidebar-column.sidebar.sticky-column::-webkit-scrollbar {
+  background: var(--dark-color);
+  width: 12px;
+}
+
+.sidebar-column.sidebar.sticky-column::-webkit-scrollbar-thumb {
+  transition: background 0.2s;
+  background: rgba(255, 255, 255, 0.2);
+  border: 3px solid transparent;
+  border-radius: 10px;
+  background-clip: content-box;
+}
+
+.sidebar-column.sidebar.sticky-column > h1 {
+  position: sticky;
+  top: 0;
+  margin: 0 calc(-1 * var(--content-padding));
+  margin-bottom: 10px;
+
+  border-bottom: 1px dotted rgba(220, 220, 220, 0.4);
+  padding: 10px 5px;
+
+  background: var(--bg-black-color);
+  -webkit-backdrop-filter: blur(3px);
+  backdrop-filter: blur(3px);
+}
+
 /* Image overlay */
 
 #image-overlay-container {
@@ -1575,7 +1643,7 @@ html[data-language-code="preview-en"][data-url-key="localized.home"] #content
 /* Layout - Wide (most computers) */
 
 @media (min-width: 900px) {
-  #secondary-nav:not(.no-hide) {
+  #page-container:not(.has-zero-sidebars) #secondary-nav {
     display: none;
   }
 }
@@ -1617,12 +1685,12 @@ html[data-language-code="preview-en"][data-url-key="localized.home"] #content
     z-index: 2;
   }
 
-  html[data-url-key="localized.home"] .layout-columns.has-one-sidebar .grid-listing > .grid-item:not(:nth-child(n+10)) {
+  html[data-url-key="localized.home"] #page-container.has-one-sidebar .grid-listing > .grid-item:not(:nth-child(n+10)) {
     flex-basis: 23%;
     margin: 15px;
   }
 
-  html[data-url-key="localized.home"] .layout-columns.has-one-sidebar .grid-listing > .grid-item:nth-child(n+10) {
+  html[data-url-key="localized.home"] #page-container.has-one-sidebar .grid-listing > .grid-item:nth-child(n+10) {
     flex-basis: 18%;
     margin: 10px;
   }
@@ -1692,4 +1760,8 @@ html[data-language-code="preview-en"][data-url-key="localized.home"] #content
   #header > div:not(:first-child) {
     margin-top: 0.5em;
   }
+
+  main.long-content {
+    --long-content-padding-ratio: 0.04;
+  }
 }
diff --git a/src/strings-default.json b/src/strings-default.json
index e893a5ce..6c841e72 100644
--- a/src/strings-default.json
+++ b/src/strings-default.json
@@ -197,6 +197,7 @@
   "misc.external.flash.homestuck.page": "{LINK} (page {PAGE})",
   "misc.external.flash.homestuck.secret": "{LINK} (secret page)",
   "misc.external.flash.youtube": "{LINK} (on any device)",
+  "misc.missingImage": "(This image file is missing)",
   "misc.missingLinkContent": "(Missing link content)",
   "misc.nav.previous": "Previous",
   "misc.nav.next": "Next",
@@ -266,6 +267,7 @@
   "albumGalleryPage.statsLine": "{TRACKS} totaling {DURATION}.",
   "albumGalleryPage.statsLine.withDate": "{TRACKS} totaling {DURATION}. Released {DATE}.",
   "albumGalleryPage.coverArtistsLine": "All track artwork by {ARTISTS}.",
+  "albumGalleryPage.noTrackArtworksLine": "This album doesn't have any track artwork.",
   "albumCommentaryPage.title": "{ALBUM} - Commentary",
   "albumCommentaryPage.infoLine": "{WORDS} across {ENTRIES}.",
   "albumCommentaryPage.nav.album": "Album: {ALBUM}",
@@ -321,6 +323,8 @@
   "flashIndex.title": "Flashes & Games",
   "flashPage.title": "{FLASH}",
   "flashPage.nav.flash": "{FLASH}",
+  "flashSidebar.flashList.flashesInThisAct": "Flashes in this act",
+  "flashSidebar.flashList.entriesInThisSection": "Entries in this section",
   "groupSidebar.title": "Groups",
   "groupSidebar.groupList.category": "{CATEGORY}",
   "groupSidebar.groupList.item": "{GROUP}",
@@ -335,8 +339,6 @@
   "groupInfoPage.albumList.item.otherGroupAccent": "(from {GROUP})",
   "groupGalleryPage.title": "{GROUP} - Gallery",
   "groupGalleryPage.infoLine": "{TRACKS} across {ALBUMS}, totaling {TIME}.",
-  "groupGalleryPage.anotherGroupLine": "({LINK})",
-  "groupGalleryPage.anotherGroupLine.link": "Choose another group to filter by!",
   "listingIndex.title": "Listings",
   "listingIndex.infoLine": "{WIKI}: {TRACKS} across {ALBUMS}, totaling {DURATION}.",
   "listingIndex.exploreList": "Feel free to explore any of the listings linked below and in the sidebar!",
@@ -447,15 +449,18 @@
   "listingPage.listTracks.inFlashes.byFlash.chunk.item": "{TRACK} (from {ALBUM})",
   "listingPage.listTracks.withLyrics.title": "Tracks - with Lyrics",
   "listingPage.listTracks.withLyrics.title.short": "...with Lyrics",
-  "listingPage.listTracks.withLyrics.chunk.title": "{ALBUM} ({DATE})",
+  "listingPage.listTracks.withLyrics.chunk.title": "{ALBUM}",
+  "listingPage.listTracks.withLyrics.chunk.title.withDate": "{ALBUM} ({DATE})",
   "listingPage.listTracks.withLyrics.chunk.item": "{TRACK}",
   "listingPage.listTracks.withSheetMusicFiles.title": "Tracks - with Sheet Music Files",
   "listingPage.listTracks.withSheetMusicFiles.title.short": "...with Sheet Music Files",
-  "listingPage.listTracks.withSheetMusicFiles.chunk.title": "{ALBUM} ({DATE})",
+  "listingPage.listTracks.withSheetMusicFiles.chunk.title": "{ALBUM}",
+  "listingPage.listTracks.withSheetMusicFiles.chunk.title.withDate": "{ALBUM} ({DATE})",
   "listingPage.listTracks.withSheetMusicFiles.chunk.item": "{TRACK}",
   "listingPage.listTracks.withMidiProjectFiles.title": "Tracks - with MIDI & Project Files",
   "listingPage.listTracks.withMidiProjectFiles.title.short": "...with MIDI & Project Files",
-  "listingPage.listTracks.withMidiProjectFiles.chunk.title": "{ALBUM} ({DATE})",
+  "listingPage.listTracks.withMidiProjectFiles.chunk.title": "{ALBUM}",
+  "listingPage.listTracks.withMidiProjectFiles.chunk.title.withDate": "{ALBUM} ({DATE})",
   "listingPage.listTracks.withMidiProjectFiles.chunk.item": "{TRACK}",
   "listingPage.listTags.byName.title": "Tags - by Name",
   "listingPage.listTags.byName.title.short": "...by Name",
diff --git a/src/upd8.js b/src/upd8.js
index bfdd1c2a..27445a8e 100755
--- a/src/upd8.js
+++ b/src/upd8.js
@@ -32,11 +32,13 @@
 // node.js and you'll 8e fine. ...Within the project root. O8viously.
 
 import {execSync} from 'node:child_process';
+import {readFile} from 'node:fs/promises';
 import * as path from 'node:path';
 import {fileURLToPath} from 'node:url';
 
 import wrap from 'word-wrap';
 
+import {displayCompositeCacheAnalysis} from '#composite';
 import {processLanguageFile} from '#language';
 import {isMain, traverse} from '#node-utils';
 import bootRepl from '#repl';
@@ -46,8 +48,9 @@ import {generateURLs, urlSpec} from '#urls';
 import {sortByName} from '#wiki-data';
 
 import {
-  color,
+  colors,
   decorateTime,
+  fileIssue,
   logWarn,
   logInfo,
   logError,
@@ -57,6 +60,7 @@ import {
 } from '#cli';
 
 import genThumbs, {
+  CACHE_FILE as thumbsCacheFile,
   clearThumbs,
   defaultMagickThreads,
   isThumb,
@@ -78,7 +82,7 @@ import * as buildModes from './write/build-modes/index.js';
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
 
-const CACHEBUST = 20;
+const CACHEBUST = 22;
 
 let COMMIT;
 try {
@@ -91,9 +95,64 @@ const BUILD_TIME = new Date();
 
 const DEFAULT_STRINGS_FILE = 'strings-default.json';
 
+const STATUS_NOT_STARTED       = `not started`;
+const STATUS_NOT_APPLICABLE    = `not applicable`;
+const STATUS_STARTED_NOT_DONE  = `started but not yet done`;
+const STATUS_DONE_CLEAN        = `done without warnings`;
+const STATUS_FATAL_ERROR       = `fatal error`;
+const STATUS_HAS_WARNINGS      = `has warnings`;
+
+const defaultStepStatus = {status: STATUS_NOT_STARTED, annotation: null};
+
+// Defined globally for quick access outside the main() function's contents.
+// This will be initialized and mutated over the course of main().
+let stepStatusSummary;
+let showStepStatusSummary = false;
+
 async function main() {
   Error.stackTraceLimit = Infinity;
 
+  stepStatusSummary = {
+    loadThumbnailCache:
+      {...defaultStepStatus, name: `load thumbnail cache file`},
+
+    generateThumbnails:
+      {...defaultStepStatus, name: `generate thumbnails`},
+
+    loadDataFiles:
+      {...defaultStepStatus, name: `load and process data files`},
+
+    linkWikiDataArrays:
+      {...defaultStepStatus, name: `link wiki data arrays`},
+
+    filterDuplicateDirectories:
+      {...defaultStepStatus, name: `filter duplicate directories`},
+
+    filterReferenceErrors:
+      {...defaultStepStatus, name: `filter reference errors`},
+
+    sortWikiDataArrays:
+      {...defaultStepStatus, name: `sort wiki data arrays`},
+
+    precacheData:
+      {...defaultStepStatus, name: `precache data`},
+
+    loadInternalDefaultLanguage:
+      {...defaultStepStatus, name: `load internal default language`},
+
+    loadLanguageFiles:
+      {...defaultStepStatus, name: `load custom language files`},
+
+    initializeDefaultLanguage:
+      {...defaultStepStatus, name: `initialize default language`},
+
+    preloadFileSizes:
+      {...defaultStepStatus, name: `preload file sizes`},
+
+    performBuild:
+      {...defaultStepStatus, name: `perform selected build mode`},
+  };
+
   const defaultQueueSize = 500;
 
   const buildModeFlagOptions = (
@@ -118,7 +177,7 @@ async function main() {
   } else if (selectedBuildModeFlags.length > 1) {
     logError`Building multiple modes (${selectedBuildModeFlags.join(', ')}) at once not supported.`;
     logError`Please specify a maximum of one build mode.`;
-    return;
+    return false;
   } else {
     selectedBuildModeFlag = selectedBuildModeFlags[0];
     usingDefaultBuildMode = false;
@@ -218,6 +277,11 @@ async function main() {
       type: 'flag',
     },
 
+    'show-step-summary': {
+      help: `Show a summary of all the top-level build steps once hsmusic exits. This is mostly useful for progammer debugging!`,
+      type: 'flag',
+    },
+
     'queue-size': {
       help: `Process more or fewer disk files at once to optimize performance or avoid I/O errors, unlimited if set to 0 (between 500 and 700 is usually a safe range for building HSMusic on Windows machines)\nDefaults to ${defaultQueueSize}`,
       type: 'value',
@@ -231,6 +295,12 @@ async function main() {
 
     'magick-threads': {
       help: `Process more or fewer thumbnail files at once with ImageMagick when generating thumbnails. (Each ImageMagick thread may also make use of multi-core processing at its own utility.)`,
+      type: 'value',
+      validate(threads) {
+        if (parseInt(threads) !== parseFloat(threads)) return 'an integer';
+        if (parseInt(threads) < 0) return 'a counting number or zero';
+        return true;
+      }
     },
     magick: {alias: 'magick-threads'},
 
@@ -271,7 +341,7 @@ async function main() {
     const indentWrap = (spaces, str) => wrap(str, {width: 60 - spaces, indent: ' '.repeat(spaces)});
 
     const showOptions = (msg, options) => {
-      console.log(color.bright(msg));
+      console.log(colors.bright(msg));
 
       const entries = Object.entries(options);
       const sortedOptions = sortByName(entries
@@ -302,13 +372,13 @@ async function main() {
           console.log('');
         }
 
-        console.log(color.bright(` --` + name) +
+        console.log(colors.bright(` --` + name) +
           (aliases.length
-            ? ` (or: ${aliases.map(alias => color.bright(`--` + alias)).join(', ')})`
+            ? ` (or: ${aliases.map(alias => colors.bright(`--` + alias)).join(', ')})`
             : '') +
           (descriptor.help
             ? ''
-            : color.dim('  (no help provided)')));
+            : colors.dim('  (no help provided)')));
 
         if (wrappedHelp) {
           console.log(wrappedHelp);
@@ -328,7 +398,7 @@ async function main() {
     };
 
     console.log(
-      color.bright(`hsmusic (aka. Homestuck Music Wiki)\n`) +
+      colors.bright(`hsmusic (aka. Homestuck Music Wiki)\n`) +
       `static wiki software cataloguing collaborative creation\n`);
 
     console.log(indentWrap(0,
@@ -352,7 +422,7 @@ async function main() {
       })`, buildOptions);
     }
 
-    return;
+    return true;
   }
 
   const dataPath = cliOptions['data-path'] || process.env.HSMUSIC_DATA;
@@ -364,6 +434,8 @@ async function main() {
   const clearThumbsFlag = cliOptions['clear-thumbs'] ?? false;
   const noBuild = cliOptions['no-build'] ?? false;
 
+  showStepStatusSummary = cliOptions['show-step-summary'] ?? false;
+
   const replFlag = cliOptions['repl'] ?? false;
   const disableReplHistory = cliOptions['no-repl-history'] ?? false;
 
@@ -379,19 +451,16 @@ async function main() {
 
   const magickThreads = +(cliOptions['magick-threads'] ?? defaultMagickThreads);
 
-  {
-    let errored = false;
-    const error = (cond, msg) => {
-      if (cond) {
-        console.error(`\x1b[31;1m${msg}\x1b[0m`);
-        errored = true;
-      }
-    };
-    error(!dataPath, `Expected --data-path option or HSMUSIC_DATA to be set`);
-    error(!mediaPath, `Expected --media-path option or HSMUSIC_MEDIA to be set`);
-    if (errored) {
-      return;
-    }
+  if (!dataPath) {
+    logError`${`Expected --data-path option or HSMUSIC_DATA to be set`}`;
+  }
+
+  if (!mediaPath) {
+    logError`${`Expected --media-path option or HSMUSIC_MEDIA to be set`}`;
+  }
+
+  if (!dataPath || !mediaPath) {
+    return false;
   }
 
   if (replFlag) {
@@ -414,31 +483,103 @@ async function main() {
 
   if (skipThumbs && thumbsOnly) {
     logInfo`Well, you've put yourself rather between a roc and a hard place, hmmmm?`;
-    return;
+    return false;
   }
 
   if (clearThumbsFlag) {
-    await clearThumbs(mediaPath, {queueSize});
-
-    logInfo`All done! Remove ${'--clear-thumbs'} to run the next build.`;
-    if (skipThumbs) {
-      logInfo`And don't forget to remove ${'--skip-thumbs'} too, eh?`;
+    const result = await clearThumbs(mediaPath, {queueSize});
+    if (result.success) {
+      logInfo`All done! Remove ${'--clear-thumbs'} to run the next build.`;
+      if (skipThumbs) {
+        logInfo`And don't forget to remove ${'--skip-thumbs'} too, eh?`;
+      }
     }
-    return;
+    return true;
   }
 
+  let thumbsCache;
+
   if (skipThumbs) {
+    Object.assign(stepStatusSummary.generateThumbnails, {
+      status: STATUS_NOT_APPLICABLE,
+      annotation: `provided --skip-thumbs`,
+    });
+
+    stepStatusSummary.loadThumbnailCache.status = STATUS_STARTED_NOT_DONE;
+
+    const thumbsCachePath = path.join(mediaPath, thumbsCacheFile);
+
+    try {
+      thumbsCache = JSON.parse(await readFile(thumbsCachePath));
+      logInfo`Thumbnail cache file successfully read.`;
+      stepStatusSummary.loadThumbnailCache.status = STATUS_DONE_CLEAN;
+    } catch (error) {
+      if (error.code === 'ENOENT') {
+        logError`The thumbnail cache doesn't exist, and it's necessary to build`
+        logError`the website. Please run once without ${'--skip-thumbs'} - after`
+        logError`that you'll be good to go and don't need to process thumbnails`
+        logError`again!`;
+
+        Object.assign(stepStatusSummary.loadThumbnailCache, {
+          status: STATUS_FATAL_ERROR,
+          annotation: `cache does not exist`,
+        });
+
+        return false;
+      } else {
+        logError`Malformed or unreadable thumbnail cache file: ${error}`;
+        logError`Path: ${thumbsCachePath}`;
+        logError`The thumbbnail cache is necessary to build the site, so you'll`;
+        logError`have to investigate this to get the build working. Try running`;
+        logError`again without ${'--skip-thumbs'}. If you can't get it working,`;
+        logError`you're welcome to message in the HSMusic Discord and we'll try`;
+        logError`to help you out with troubleshooting!`;
+        logError`${'https://hsmusic.wiki/discord/'}`;
+
+        Object.assign(stepStatusSummary.loadThumbnailCache, {
+          status: STATUS_FATAL_ERROR,
+          annotation: `cache malformed or unreadable`,
+        });
+
+        return false;
+      }
+    }
+
     logInfo`Skipping thumbnail generation.`;
   } else {
+    Object.assign(stepStatusSummary.loadThumbnailCache, {
+      status: STATUS_NOT_APPLICABLE,
+      annotation: `using cache from thumbnail generation`,
+    });
+
+    stepStatusSummary.generateThumbnails.status = STATUS_STARTED_NOT_DONE;
+
     logInfo`Begin thumbnail generation... -----+`;
+
     const result = await genThumbs(mediaPath, {
       queueSize,
       magickThreads,
       quiet: !thumbsOnly,
     });
+
     logInfo`Done thumbnail generation! --------+`;
-    if (!result) return;
-    if (thumbsOnly) return;
+
+    if (!result.success) {
+      Object.assign(stepStatusSummary.generateThumbnails, {
+        status: STATUS_FATAL_ERROR,
+        annotation: `view log for details`,
+      });
+
+      return false;
+    }
+
+    stepStatusSummary.generateThumbnails.status = STATUS_DONE_CLEAN;
+
+    if (thumbsOnly) {
+      return true;
+    }
+
+    thumbsCache = result.cache;
   }
 
   if (noBuild) {
@@ -453,14 +594,32 @@ async function main() {
     CacheableObject.DEBUG_SLOW_TRACK_INVALID_PROPERTIES = true;
   }
 
-  const {aggregate: processDataAggregate, result: wikiDataResult} =
-    await loadAndProcessDataDocuments({dataPath});
+  stepStatusSummary.loadDataFiles.status = STATUS_STARTED_NOT_DONE;
+
+  let processDataAggregate, wikiDataResult;
+
+  try {
+    ({aggregate: processDataAggregate, result: wikiDataResult} =
+        await loadAndProcessDataDocuments({dataPath}));
+  } catch (error) {
+    console.error(error);
+
+    logError`There was a JavaScript error loading data files.`;
+    fileIssue();
+
+    Object.assign(stepStatusSummary.loadDataFiles, {
+      status: STATUS_FATAL_ERROR,
+      annotation: `javascript error - view log for details`,
+    });
+
+    return false;
+  }
 
   Object.assign(wikiData, wikiDataResult);
 
   {
     const logThings = (thingDataProp, label) =>
-      logInfo` - ${wikiData[thingDataProp]?.length ?? color.red('(Missing!)')} ${color.normal(color.dim(label))}`;
+      logInfo` - ${wikiData[thingDataProp]?.length ?? colors.red('(Missing!)')} ${colors.normal(colors.dim(label))}`;
     try {
       logInfo`Loaded data and processed objects:`;
       logThings('albumData', 'albums');
@@ -499,84 +658,105 @@ async function main() {
       logWarn`still build - but all errored data will be skipped.`;
       logWarn`(Resolve errors for more complete output!)`;
       errorless = false;
-    }
 
-    if (errorless) {
-      logInfo`All data processed without any errors - nice!`;
-      logInfo`(This means all source files will be fully accounted for during page generation.)`;
+      Object.assign(stepStatusSummary.loadDataFiles, {
+        status: STATUS_HAS_WARNINGS,
+        annotation: `view log for details`,
+      });
     }
-  }
 
-  if (!wikiData.wikiInfo) {
-    logError`Can't proceed without wiki info file (${WIKI_INFO_FILE}) successfully loading`;
-    return;
-  }
+    if (!wikiData.wikiInfo) {
+      logError`Can't proceed without wiki info file (${WIKI_INFO_FILE}) successfully loading`;
 
-  let duplicateDirectoriesErrored = false;
+      Object.assign(stepStatusSummary.loadDataFiles, {
+        status: STATUS_FATAL_ERROR,
+        annotation: `wiki info object not available`,
+      });
 
-  function filterAndShowDuplicateDirectories() {
-    const aggregate = filterDuplicateDirectories(wikiData);
-    let errorless = true;
-    try {
-      aggregate.close();
-    } catch (aggregate) {
-      niceShowAggregate(aggregate);
-      logWarn`The above duplicate directories were detected while reviewing data files.`;
-      logWarn`Each thing listed above will been totally excempt from this build of the site!`;
-      logWarn`Specify unique 'Directory' fields in data entries to resolve these.`;
-      logWarn`${`Note:`} This will probably result in reference errors below.`;
-      logWarn`${`. . .`} You should fix duplicate directories first!`;
-      logWarn`(Resolve errors for more complete output!)`;
-      duplicateDirectoriesErrored = true;
-      errorless = false;
-    }
-    if (errorless) {
-      logInfo`No duplicate directories found - nice!`;
+      return false;
     }
-  }
 
-  function filterAndShowReferenceErrors() {
-    const aggregate = filterReferenceErrors(wikiData);
-    let errorless = true;
-    try {
-      aggregate.close();
-    } catch (error) {
-      niceShowAggregate(error);
-      logWarn`The above errors were detected while validating references in data files.`;
-      logWarn`If the remaining valid data is complete enough, the wiki will still build -`;
-      logWarn`but all errored references will be skipped.`;
-      if (duplicateDirectoriesErrored) {
-        logWarn`${`Note:`} Duplicate directories were found as well. Review those first,`;
-        logWarn`${`. . .`} as they may have caused some of the errors detected above.`;
-      }
-      logWarn`(Resolve errors for more complete output!)`;
-      errorless = false;
-    }
     if (errorless) {
-      logInfo`All references validated without any errors - nice!`;
-      logInfo`(This means all references between things, such as leitmotif references`;
-      logInfo` and artist credits, will be fully accounted for during page generation.)`;
+      logInfo`All data files processed without any errors - nice!`;
+      stepStatusSummary.loadDataFiles.status = STATUS_DONE_CLEAN;
     }
   }
 
   // Link data arrays so that all essential references between objects are
   // complete, so properties (like dates!) are inherited where that's
   // appropriate.
+
+  stepStatusSummary.linkWikiDataArrays.status = STATUS_STARTED_NOT_DONE;
+
   linkWikiDataArrays(wikiData);
 
+  stepStatusSummary.linkWikiDataArrays.status = STATUS_DONE_CLEAN;
+
   // Filter out any things with duplicate directories throughout the data,
   // warning about them too.
-  filterAndShowDuplicateDirectories();
+
+  stepStatusSummary.filterDuplicateDirectories.status = STATUS_STARTED_NOT_DONE;
+
+  const filterDuplicateDirectoriesAggregate =
+    filterDuplicateDirectories(wikiData);
+
+  try {
+    filterDuplicateDirectoriesAggregate.close();
+    logInfo`No duplicate directories found - nice!`;
+    stepStatusSummary.filterDuplicateDirectories.status = STATUS_DONE_CLEAN;
+  } catch (aggregate) {
+    niceShowAggregate(aggregate);
+
+    logWarn`The above duplicate directories were detected while reviewing data files.`;
+    logWarn`Since it's impossible to automatically determine which one's directory is`;
+    logWarn`correct, the build can't continue. Specify unique 'Directory' fields in`;
+    logWarn`some or all of these data entries to resolve the errors.`;
+
+    Object.assign(stepStatusSummary.filterDuplicateDirectories, {
+      status: STATUS_FATAL_ERROR,
+      annotation: `duplicate directories found`,
+    });
+
+    return false;
+  }
 
   // Filter out any reference errors throughout the data, warning about them
   // too.
-  filterAndShowReferenceErrors();
+
+  stepStatusSummary.filterReferenceErrors.status = STATUS_STARTED_NOT_DONE;
+
+  const filterReferenceErrorsAggregate = filterReferenceErrors(wikiData);
+
+  try {
+    filterReferenceErrorsAggregate.close();
+    logInfo`All references validated without any errors - nice!`;
+    stepStatusSummary.filterReferenceErrors.status = STATUS_DONE_CLEAN;
+  } catch (error) {
+    niceShowAggregate(error);
+
+    logWarn`The above errors were detected while validating references in data files.`;
+    logWarn`The wiki will still build, but these connections between data objects`;
+    logWarn`will be completely skipped. Resolve the errors for more complete output.`;
+
+    Object.assign(stepStatusSummary.filterReferenceErrors, {
+      status: STATUS_HAS_WARNINGS,
+      annotation: `view log for details`,
+    });
+  }
 
   // Sort data arrays so that they're all in order! This may use properties
   // which are only available after the initial linking.
+
+  stepStatusSummary.sortWikiDataArrays.status = STATUS_STARTED_NOT_DONE;
+
   sortWikiDataArrays(wikiData);
 
+  stepStatusSummary.sortWikiDataArrays.status = STATUS_DONE_CLEAN;
+
   if (precacheData) {
+    stepStatusSummary.precacheData.status = STATUS_STARTED_NOT_DONE;
+
+    // TODO: Aggregate errors here, instead of just throwing.
     progressCallAll('Caching all data values', Object.entries(wikiData)
       .filter(([key]) =>
         key !== 'listingSpec' &&
@@ -587,27 +767,96 @@ async function main() {
         [key, value])
       .flatMap(([_key, things]) => things)
       .map(thing => () => CacheableObject.cacheAllExposedProperties(thing)));
+
+    stepStatusSummary.precacheData.status = STATUS_DONE_CLEAN;
+  } else {
+    Object.assign(stepStatusSummary.precacheData, {
+      status: STATUS_NOT_APPLICABLE,
+      annotation: `--precache-data not provided`,
+    });
+  }
+
+  if (noBuild) {
+    Object.assign(stepStatusSummary.performBuild, {
+      status: STATUS_NOT_APPLICABLE,
+      annotation: `--no-build provided`,
+    });
+
+    displayCompositeCacheAnalysis();
+
+    if (precacheData) {
+      return true;
+    }
   }
 
-  const internalDefaultLanguage = await processLanguageFile(
-    path.join(__dirname, DEFAULT_STRINGS_FILE));
+  let internalDefaultLanguage;
+
+  try {
+    internalDefaultLanguage =
+      await processLanguageFile(path.join(__dirname, DEFAULT_STRINGS_FILE));
+
+    stepStatusSummary.loadInternalDefaultLanguage.status = STATUS_DONE_CLEAN;
+  } catch (error) {
+    console.error(error);
+
+    logError`There was an error reading the internal language file.`;
+    fileIssue();
+
+    Object.assign(stepStatusSummary.loadInternalDefaultLanguage, {
+      status: STATUS_FATAL_ERROR,
+      annotation: `see log for details`,
+    });
+
+    return false;
+  }
 
   let languages;
+
   if (langPath) {
+    stepStatusSummary.loadLanguageFiles.status = STATUS_STARTED_NOT_DONE;
+
     const languageDataFiles = await traverse(langPath, {
       filterFile: name => path.extname(name) === '.json',
       pathStyle: 'device',
     });
 
-    const results = await progressPromiseAll(`Reading & processing language files.`,
-      languageDataFiles.map((file) => processLanguageFile(file)));
+    let results;
 
-    languages = Object.fromEntries(
-      results.map((language) => [language.code, language]));
+    // TODO: Aggregate errors (with Promise.allSettled).
+    try {
+      results =
+        await progressPromiseAll(`Reading & processing language files.`,
+          languageDataFiles.map((file) => processLanguageFile(file)));
+    } catch (error) {
+      console.error(error);
+
+      logError`Failed to load language files. Please investigate these, or don't provide`;
+      logError`--lang-path (or HSMUSIC_LANG) and build again.`;
+
+      Object.assign(stepStatusSummary.loadLanguageFiles, {
+        status: STATUS_FATAL_ERROR,
+        annotation: `see log for details`,
+      });
+
+      return false;
+    }
+
+    languages =
+      Object.fromEntries(
+        results.map((language) => [language.code, language]));
+
+    stepStatusSummary.loadLanguageFiles.status = STATUS_DONE_CLEAN;
   } else {
     languages = {};
+
+    Object.assign(stepStatusSummary.loadLanguageFiles, {
+      status: STATUS_NOT_APPLICABLE,
+      annotation: `--lang-path and HSMUSIC_LANG not provided`,
+    });
   }
 
+  stepStatusSummary.initializeDefaultLanguage.status = STATUS_STARTED_NOT_DONE;
+
   const customDefaultLanguage =
     languages[wikiData.wikiInfo.defaultLanguage ?? internalDefaultLanguage.code];
   let finalDefaultLanguage;
@@ -616,17 +865,34 @@ async function main() {
     logInfo`Applying new default strings from custom ${customDefaultLanguage.code} language file.`;
     customDefaultLanguage.inheritedStrings = internalDefaultLanguage.strings;
     finalDefaultLanguage = customDefaultLanguage;
+
+    Object.assign(stepStatusSummary.initializeDefaultLanguage, {
+      status: STATUS_DONE_CLEAN,
+      annotation: `using wiki-specified custom default language`,
+    });
   } else if (wikiData.wikiInfo.defaultLanguage) {
     logError`Wiki info file specified default language is ${wikiData.wikiInfo.defaultLanguage}, but no such language file exists!`;
     if (langPath) {
       logError`Check if an appropriate file exists in ${langPath}?`;
     } else {
-      logError`Be sure to specify ${'--lang'} or ${'HSMUSIC_LANG'} with the path to language files.`;
+      logError`Be sure to specify ${'--lang-path'} or ${'HSMUSIC_LANG'} with the path to language files.`;
     }
-    return;
+
+    Object.assign(stepStatusSummary.initializeDefaultLanguage, {
+      status: STATUS_FATAL_ERROR,
+      annotation: `wiki specifies default language whose file is not available`,
+    });
+
+    return false;
   } else {
     languages[internalDefaultLanguage.code] = internalDefaultLanguage;
     finalDefaultLanguage = internalDefaultLanguage;
+    stepStatusSummary.initializeDefaultLanguage.status = STATUS_DONE_CLEAN;
+
+    Object.assign(stepStatusSummary.initializeDefaultLanguage, {
+      status: STATUS_DONE_CLEAN,
+      annotation: `no custom default language specified`,
+    });
   }
 
   for (const language of Object.values(languages)) {
@@ -641,7 +907,8 @@ async function main() {
 
   const urls = generateURLs(urlSpec);
 
-  await verifyImagePaths(mediaPath, {urls, wikiData});
+  const {missing: missingImagePaths} =
+    await verifyImagePaths(mediaPath, {urls, wikiData});
 
   const fileSizePreloader = new FileSizePreloader();
 
@@ -704,7 +971,9 @@ async function main() {
   };
 
   const getSizeOfAdditionalFile = getSizeOfMediaFileHelper(additionalFilePaths);
-  const getSizeOfImageFile = getSizeOfMediaFileHelper(imageFilePaths);
+  const getSizeOfImagePath = getSizeOfMediaFileHelper(imageFilePaths);
+
+  stepStatusSummary.preloadFileSizes.status = STATUS_STARTED_NOT_DONE;
 
   logInfo`Preloading filesizes for ${additionalFilePaths.length} additional files...`;
 
@@ -716,9 +985,23 @@ async function main() {
   fileSizePreloader.loadPaths(...imageFilePaths.map((path) => path.device));
   await fileSizePreloader.waitUntilDoneLoading();
 
-  logInfo`Done preloading filesizes!`;
+  if (fileSizePreloader.hasErrored) {
+    logWarn`Some media files couldn't be read for preloading filesizes.`;
+    logWarn`This means the wiki won't display file sizes for these files.`;
+    logWarn`Investigate missing or unreadable files to get that fixed!`;
 
-  if (noBuild) return;
+    Object.assign(stepStatusSummary.preloadFileSizes, {
+      status: STATUS_HAS_WARNINGS,
+      annotation: `see log for details`,
+    });
+  } else {
+    logInfo`Done preloading filesizes without any errors - nice!`;
+    stepStatusSummary.preloadFileSizes.status = STATUS_DONE_CLEAN;
+  }
+
+  if (noBuild) {
+    return true;
+  }
 
   const developersComment =
     `<!--\n` + [
@@ -750,25 +1033,58 @@ async function main() {
       .map(line => `    ` + line)
       .join('\n') + `\n-->`;
 
-  return selectedBuildMode.go({
-    cliOptions,
-    dataPath,
-    mediaPath,
-    queueSize,
-    srcRootPath: __dirname,
-
-    defaultLanguage: finalDefaultLanguage,
-    languages,
-    wikiData,
-    urls,
-    urlSpec,
-
-    cachebust: '?' + CACHEBUST,
-    developersComment,
-    getSizeOfAdditionalFile,
-    getSizeOfImageFile,
-    niceShowAggregate,
-  });
+  stepStatusSummary.performBuild.status = STATUS_STARTED_NOT_DONE;
+
+  let buildModeResult;
+
+  try {
+    buildModeResult = await selectedBuildMode.go({
+      cliOptions,
+      dataPath,
+      mediaPath,
+      queueSize,
+      srcRootPath: __dirname,
+
+      defaultLanguage: finalDefaultLanguage,
+      languages,
+      missingImagePaths,
+      thumbsCache,
+      urls,
+      urlSpec,
+      wikiData,
+
+      cachebust: '?' + CACHEBUST,
+      developersComment,
+      getSizeOfAdditionalFile,
+      getSizeOfImagePath,
+      niceShowAggregate,
+    });
+  } catch (error) {
+    console.error(error);
+
+    logError`There was a JavaScript error performing the build.`;
+    fileIssue();
+
+    Object.assign(stepStatusSummary.performBuild, {
+      status: STATUS_FATAL_ERROR,
+      message: `javascript error - view log for details`,
+    });
+
+    return false;
+  }
+
+  if (buildModeResult !== true) {
+    Object.assign(stepStatusSummary.performBuild, {
+      status: STATUS_HAS_WARNINGS,
+      message: `may not have completed - view log for details`,
+    });
+
+    return false;
+  }
+
+  stepStatusSummary.performBuild.status = STATUS_DONE_CLEAN;
+
+  return true;
 }
 
 // TODO: isMain detection isn't consistent across platforms here
@@ -787,6 +1103,65 @@ if (true || isMain(import.meta.url) || path.basename(process.argv[1]) === 'hsmus
       }
     }
 
+    if (showStepStatusSummary) {
+      console.error(colors.bright(`Step summary:`));
+
+      const longestNameLength =
+        Math.max(...
+          Object.values(stepStatusSummary)
+            .map(({name}) => name.length));
+
+      const anyStepsNotClean =
+        Object.values(stepStatusSummary)
+          .some(({status}) =>
+            status === STATUS_HAS_WARNINGS ||
+            status === STATUS_FATAL_ERROR ||
+            status === STATUS_STARTED_NOT_DONE);
+
+      for (const {name, status, annotation} of Object.values(stepStatusSummary)) {
+        let message = `${(name + ': ').padEnd(longestNameLength + 4, '.')} ${status}`;
+        if (annotation) {
+          message += ` (${annotation})`;
+        }
+
+        switch (status) {
+          case STATUS_DONE_CLEAN:
+            console.error(colors.green(message));
+            break;
+
+          case STATUS_NOT_STARTED:
+          case STATUS_NOT_APPLICABLE:
+            console.error(colors.dim(message));
+            break;
+
+          case STATUS_HAS_WARNINGS:
+          case STATUS_STARTED_NOT_DONE:
+            console.error(colors.yellow(message));
+            break;
+
+          case STATUS_FATAL_ERROR:
+            console.error(colors.red(message));
+            break;
+
+          default:
+            console.error(message);
+            break;
+        }
+      }
+
+      if (result === true) {
+        if (anyStepsNotClean) {
+          console.error(colors.bright(`Final output is true, but some steps aren't clean.`));
+          process.exit(1);
+          return;
+        } else {
+          console.error(colors.bright(`Final output is true and all steps are clean.`));
+        }
+      } else {
+        console.error(colors.bright(`Final output is not true (${result}).`));
+      }
+    }
+
     if (result !== true) {
       process.exit(1);
       return;
diff --git a/src/url-spec.js b/src/url-spec.js
index 4d103134..2ff0fa5b 100644
--- a/src/url-spec.js
+++ b/src/url-spec.js
@@ -37,6 +37,8 @@ const urlSpec = {
       flashIndex: 'flash/',
       flash: 'flash/<>/',
 
+      flashActGallery: 'flash-act/<>/',
+
       groupInfo: 'group/<>/',
       groupGallery: 'group/<>/gallery/',
 
diff --git a/src/util/cli.js b/src/util/cli.js
index f83c8061..4c08c085 100644
--- a/src/util/cli.js
+++ b/src/util/cli.js
@@ -17,7 +17,7 @@ export const ENABLE_COLOR =
 const C = (n) =>
   ENABLE_COLOR ? (text) => `\x1b[${n}m${text}\x1b[0m` : (text) => text;
 
-export const color = {
+export const colors = {
   bright: C('1'),
   dim: C('2'),
   normal: C('22'),
@@ -334,7 +334,9 @@ export function progressCallAll(msgOrMsgFn, array) {
 export function fileIssue({
   topMessage = `This shouldn't happen.`,
 } = {}) {
-  console.error(color.red(`${topMessage} Please let the HSMusic developers know:`));
-  console.error(color.red(`- https://hsmusic.wiki/feedback/`));
-  console.error(color.red(`- https://github.com/hsmusic/hsmusic-wiki/issues/`));
+  if (topMessage) {
+    console.error(colors.red(`${topMessage} Please let the HSMusic developers know:`));
+  }
+  console.error(colors.red(`- https://hsmusic.wiki/feedback/`));
+  console.error(colors.red(`- https://github.com/hsmusic/hsmusic-wiki/issues/`));
 }
diff --git a/src/util/html.js b/src/util/html.js
index a311bbba..282a52da 100644
--- a/src/util/html.js
+++ b/src/util/html.js
@@ -2,7 +2,7 @@
 
 import {inspect} from 'node:util';
 
-import {empty} from '#sugar';
+import {empty, typeAppearance} from '#sugar';
 import * as commonValidators from '#validators';
 
 // COMPREHENSIVE!
@@ -242,7 +242,7 @@ export class Tag {
       this.selfClosing &&
       !(value === null ||
         value === undefined ||
-        !Boolean(value) ||
+        !value ||
         Array.isArray(value) && value.filter(Boolean).length === 0)
     ) {
       throw new Error(`Tag <${this.tagName}> is self-closing but got content`);
@@ -633,7 +633,7 @@ export class Template {
 
   static validateDescription(description) {
     if (typeof description !== 'object') {
-      throw new TypeError(`Expected object, got ${typeof description}`);
+      throw new TypeError(`Expected object, got ${typeAppearance(description)}`);
     }
 
     if (description === null) {
@@ -806,24 +806,43 @@ export class Template {
     }
 
     // Null is always an acceptable slot value.
-    if (value !== null) {
-      if ('validate' in description) {
-        description.validate({
-          ...commonValidators,
-          ...validators,
-        })(value);
-      }
+    if (value === null) {
+      return true;
+    }
+
+    if ('validate' in description) {
+      description.validate({
+        ...commonValidators,
+        ...validators,
+      })(value);
+    }
 
-      if ('type' in description) {
-        const {type} = description;
-        if (type === 'html') {
-          if (!isHTML(value)) {
+    if ('type' in description) {
+      switch (description.type) {
+        case 'html': {
+          if (!isHTML(value))
             throw new TypeError(`Slot expects html (tag, template or blank), got ${typeof value}`);
-          }
-        } else {
-          if (typeof value !== type) {
-            throw new TypeError(`Slot expects ${type}, got ${typeof value}`);
-          }
+
+          return true;
+        }
+
+        case 'string': {
+          // Tags and templates are valid in string arguments - they'll be
+          // stringified when exposed to the description's .content() function.
+          if (isTag(value) || isTemplate(value))
+            return true;
+
+          if (typeof value !== 'string')
+            throw new TypeError(`Slot expects string, got ${typeof value}`);
+
+          return true;
+        }
+
+        default: {
+          if (typeof value !== description.type)
+            throw new TypeError(`Slot expects ${description.type}, got ${typeof value}`);
+
+          return true;
         }
       }
     }
@@ -847,6 +866,12 @@ export class Template {
       return providedValue;
     }
 
+    if (description.type === 'string') {
+      if (isTag(providedValue) || isTemplate(providedValue)) {
+        return providedValue.toString();
+      }
+    }
+
     if (providedValue !== null) {
       return providedValue;
     }
diff --git a/src/util/replacer.js b/src/util/replacer.js
index c5289cc5..095ee060 100644
--- a/src/util/replacer.js
+++ b/src/util/replacer.js
@@ -5,9 +5,8 @@
 // function, which converts nodes parsed here into actual HTML, links, etc
 // for embedding in a wiki webpage.
 
-import {logError, logWarn} from '#cli';
 import * as html from '#html';
-import {escapeRegex} from '#sugar';
+import {escapeRegex, typeAppearance} from '#sugar';
 
 // Syntax literals.
 const tagBeginning = '[[';
@@ -408,7 +407,7 @@ export function postprocessHeadings(inputNodes) {
 
 export function parseInput(input) {
   if (typeof input !== 'string') {
-    throw new TypeError(`Expected input to be string, got ${input}`);
+    throw new TypeError(`Expected input to be string, got ${typeAppearance(input)}`);
   }
 
   try {
diff --git a/src/util/sugar.js b/src/util/sugar.js
index 487c093c..3e39e98f 100644
--- a/src/util/sugar.js
+++ b/src/util/sugar.js
@@ -6,7 +6,7 @@
 // It will likely only do exactly what I want it to, and only in the cases I
 // decided were relevant enough to 8other handling.
 
-import {color} from './cli.js';
+import {colors} from './cli.js';
 
 // Apparently JavaScript doesn't come with a function to split an array into
 // chunks! Weird. Anyway, this is an awesome place to use a generator, even
@@ -82,7 +82,7 @@ export function stitchArrays(keyToArray) {
   for (const [key, value] of Object.entries(keyToArray)) {
     if (value === null) continue;
     if (Array.isArray(value)) continue;
-    errors.push(new TypeError(`(${key}) Expected array or null, got ${value}`));
+    errors.push(new TypeError(`(${key}) Expected array or null, got ${typeAppearance(value)}`));
   }
 
   if (!empty(errors)) {
@@ -168,12 +168,34 @@ export function setIntersection(set1, set2) {
   return intersection;
 }
 
-export function filterProperties(obj, properties) {
-  const set = new Set(properties);
-  return Object.fromEntries(
-    Object
-      .entries(obj)
-      .filter(([key]) => set.has(key)));
+export function filterProperties(object, properties, {
+  preserveOriginalOrder = false,
+} = {}) {
+  if (typeof object !== 'object' || object === null) {
+    throw new TypeError(`Expected object to be an object, got ${typeAppearance(object)}`);
+  }
+
+  if (!Array.isArray(properties)) {
+    throw new TypeError(`Expected properties to be an array, got ${typeAppearance(properties)}`);
+  }
+
+  const filteredObject = {};
+
+  if (preserveOriginalOrder) {
+    for (const property of Object.keys(object)) {
+      if (properties.includes(property)) {
+        filteredObject[property] = object[property];
+      }
+    }
+  } else {
+    for (const property of properties) {
+      if (Object.hasOwn(object, property)) {
+        filteredObject[property] = object[property];
+      }
+    }
+  }
+
+  return filteredObject;
 }
 
 export function queue(array, max = 50) {
@@ -218,6 +240,16 @@ export function escapeRegex(string) {
   return string.replace(/[-/\\^$*+?.()|[\]{}]/g, '\\$&');
 }
 
+// Gets the "look" of some arbitrary value. It's like typeof, but smarter.
+// Don't use this for actually validating types - it's only suitable for
+// inclusion in error messages.
+export function typeAppearance(value) {
+  if (value === null) return 'null';
+  if (value === undefined) return 'undefined';
+  if (Array.isArray(value)) return 'array';
+  return typeof value;
+}
+
 // Binds default values for arguments in a {key: value} type function argument
 // (typically the second argument, but may be overridden by providing a
 // [bindOpts.bindIndex] argument). Typically useful for preparing a function for
@@ -532,15 +564,17 @@ export function showAggregate(topError, {
   print = true,
 } = {}) {
   const recursive = (error, {level}) => {
-    let header = showTraces
+    let headerPart = showTraces
       ? `[${error.constructor.name || 'unnamed'}] ${
           error.message || '(no message)'
         }`
       : error instanceof AggregateError
       ? `[${error.message || '(no message)'}]`
       : error.message || '(no message)';
+
     if (showTraces) {
       const stackLines = error.stack?.split('\n');
+
       const stackLine = stackLines?.find(
         (line) =>
           line.trim().startsWith('at') &&
@@ -548,30 +582,41 @@ export function showAggregate(topError, {
           !line.includes('node:') &&
           !line.includes('<anonymous>')
       );
+
       const tracePart = stackLine
         ? '- ' +
           stackLine
             .trim()
             .replace(/file:\/\/.*\.js/, (match) => pathToFileURL(match))
         : '(no stack trace)';
-      header += ` ${color.dim(tracePart)}`;
-    }
-    const bar = level % 2 === 0 ? '\u2502' : color.dim('\u254e');
-    const head = level % 2 === 0 ? '\u257f' : color.dim('\u257f');
-
-    if (error instanceof AggregateError) {
-      return (
-        header +
-        '\n' +
-        error.errors
-          .map((error) => recursive(error, {level: level + 1}))
-          .flatMap((str) => str.split('\n'))
-          .map((line, i) => i === 0 ? ` ${head} ${line}` : ` ${bar} ${line}`)
-          .join('\n')
-      );
-    } else {
-      return header;
+
+      headerPart += ` ${colors.dim(tracePart)}`;
     }
+
+    const head1 = level % 2 === 0 ? '\u21aa' : colors.dim('\u21aa');
+    const bar1 = ' ';
+
+    const causePart =
+      (error.cause
+        ? recursive(error.cause, {level: level + 1})
+            .split('\n')
+            .map((line, i) => i === 0 ? ` ${head1} ${line}` : ` ${bar1} ${line}`)
+            .join('\n')
+        : '');
+
+    const head2 = level % 2 === 0 ? '\u257f' : colors.dim('\u257f');
+    const bar2 = level % 2 === 0 ? '\u2502' : colors.dim('\u254e');
+
+    const aggregatePart =
+      (error instanceof AggregateError
+        ? error.errors
+            .map(error => recursive(error, {level: level + 1}))
+            .flatMap(str => str.split('\n'))
+            .map((line, i) => i === 0 ? ` ${head2} ${line}` : ` ${bar2} ${line}`)
+            .join('\n')
+        : '');
+
+    return [headerPart, causePart, aggregatePart].filter(Boolean).join('\n');
   };
 
   const message = recursive(topError, {level: 0});
@@ -588,7 +633,8 @@ export function decorateErrorWithIndex(fn) {
     try {
       return fn(x, index, array);
     } catch (error) {
-      error.message = `(${color.yellow(`#${index + 1}`)}) ${error.message}`;
+      error.message = `(${colors.yellow(`#${index + 1}`)}) ${error.message}`;
+      error[Symbol.for('hsmusic.decorate.indexInSourceArray')] = index;
       throw error;
     }
   };
diff --git a/src/util/urls.js b/src/util/urls.js
index d2b303e9..11b9b8b0 100644
--- a/src/util/urls.js
+++ b/src/util/urls.js
@@ -237,27 +237,6 @@ export function getPagePathname({
     : to('localized.' + pagePath[0], ...pagePath.slice(1)));
 }
 
-export function getPagePathnameAcrossLanguages({
-  defaultLanguage,
-  languages,
-  pagePath,
-  urls,
-}) {
-  return withEntries(languages, entries => entries
-    .filter(([key, language]) => key !== 'default' && !language.hidden)
-    .map(([_key, language]) => [
-      language.code,
-      getPagePathname({
-        baseDirectory:
-          (language === defaultLanguage
-            ? ''
-            : language.code),
-        pagePath,
-        urls,
-      }),
-    ]));
-}
-
 // Needed for the rare path arguments which themselves contains one or more
 // slashes, e.g. for listings, with arguments like 'albums/by-name'.
 export function getPageSubdirectoryPrefix({
diff --git a/src/util/wiki-data.js b/src/util/wiki-data.js
index ad2f82fb..0790ae91 100644
--- a/src/util/wiki-data.js
+++ b/src/util/wiki-data.js
@@ -1,6 +1,6 @@
 // Utility functions for interacting with wiki data.
 
-import {accumulateSum, empty, stitchArrays, unique} from './sugar.js';
+import {accumulateSum, empty, unique} from './sugar.js';
 
 // Generic value operations
 
@@ -610,20 +610,9 @@ export function sortFlashesChronologically(data, {
   latestFirst = false,
   getDate,
 } = {}) {
-  // Flash acts don't actually have any identifying properties because they
-  // don't have dedicated pages (yet), so don't have a directory. Make up a
-  // fake key identifying them so flashes can be grouped together.
-  const flashActs = new Set(data.map(flash => flash.act));
-  const flashActIdentifiers = new Map();
-
-  let counter = 0;
-  for (const act of flashActs) {
-    flashActIdentifiers.set(act, ++counter);
-  }
-
   // Group flashes by act...
-  data.sort((a, b) => {
-    return flashActIdentifiers.get(a.act) - flashActIdentifiers.get(b.act);
+  sortByDirectory(data, {
+    getDirectory: flash => flash.act.directory,
   });
 
   // Sort flashes by position in act...
@@ -874,3 +863,71 @@ export function filterItemsForCarousel(items) {
     .filter(item => item.artTags.every(tag => !tag.isContentWarning))
     .slice(0, maxCarouselLayoutItems + 1);
 }
+
+// Ridiculous caching support nonsense
+
+export class TupleMap {
+  static maxNestedTupleLength = 25;
+
+  #store = [undefined, null, null, null];
+
+  #lifetime(value) {
+    if (Array.isArray(value) && value.length <= TupleMap.maxNestedTupleLength) {
+      return 'tuple';
+    } else if (
+      typeof value === 'object' && value !== null ||
+      typeof value === 'function'
+    ) {
+      return 'weak';
+    } else {
+      return 'strong';
+    }
+  }
+
+  #getSubstoreShallow(value, store) {
+    const lifetime = this.#lifetime(value);
+    const mapIndex = {weak: 1, strong: 2, tuple: 3}[lifetime];
+
+    let map = store[mapIndex];
+    if (map === null) {
+      map = store[mapIndex] =
+        (lifetime === 'weak' ? new WeakMap()
+       : lifetime === 'strong' ? new Map()
+       : lifetime === 'tuple' ? new TupleMap()
+       : null);
+    }
+
+    if (map.has(value)) {
+      return map.get(value);
+    } else {
+      const substore = [undefined, null, null, null];
+      map.set(value, substore);
+      return substore;
+    }
+  }
+
+  #getSubstoreDeep(tuple, store = this.#store) {
+    if (tuple.length === 0) {
+      return store;
+    } else {
+      const [first, ...rest] = tuple;
+      return this.#getSubstoreDeep(rest, this.#getSubstoreShallow(first, store));
+    }
+  }
+
+  get(tuple) {
+    const store = this.#getSubstoreDeep(tuple);
+    return store[0];
+  }
+
+  has(tuple) {
+    const store = this.#getSubstoreDeep(tuple);
+    return store[0] !== undefined;
+  }
+
+  set(tuple, value) {
+    const store = this.#getSubstoreDeep(tuple);
+    store[0] = value;
+    return value;
+  }
+}
diff --git a/src/write/bind-utilities.js b/src/write/bind-utilities.js
index 8e2adea7..3d4ecc7a 100644
--- a/src/write/bind-utilities.js
+++ b/src/write/bind-utilities.js
@@ -10,15 +10,24 @@ import * as html from '#html';
 import {bindOpts} from '#sugar';
 import {thumb} from '#urls';
 
+import {
+  checkIfImagePathHasCachedThumbnails,
+  getDimensionsOfImagePath,
+  getThumbnailEqualOrSmaller,
+  getThumbnailsAvailableForDimensions,
+} from '#thumbs';
+
 export function bindUtilities({
   absoluteTo,
   cachebust,
   defaultLanguage,
   getSizeOfAdditionalFile,
-  getSizeOfImageFile,
+  getSizeOfImagePath,
   language,
   languages,
+  missingImagePaths,
   pagePath,
+  thumbsCache,
   to,
   urls,
   wikiData,
@@ -30,10 +39,12 @@ export function bindUtilities({
     cachebust,
     defaultLanguage,
     getSizeOfAdditionalFile,
-    getSizeOfImageFile,
+    getSizeOfImagePath,
+    getThumbnailsAvailableForDimensions,
     html,
     language,
     languages,
+    missingImagePaths,
     pagePath,
     thumb,
     to,
@@ -46,5 +57,17 @@ export function bindUtilities({
 
   bound.find = bindFind(wikiData, {mode: 'warn'});
 
+  bound.checkIfImagePathHasCachedThumbnails =
+    (imagePath) =>
+      checkIfImagePathHasCachedThumbnails(imagePath, thumbsCache);
+
+  bound.getDimensionsOfImagePath =
+    (imagePath) =>
+      getDimensionsOfImagePath(imagePath, thumbsCache);
+
+  bound.getThumbnailEqualOrSmaller =
+    (preferred, imagePath) =>
+      getThumbnailEqualOrSmaller(preferred, imagePath, thumbsCache);
+
   return bound;
 }
diff --git a/src/write/build-modes/live-dev-server.js b/src/write/build-modes/live-dev-server.js
index 2767a02f..1339c322 100644
--- a/src/write/build-modes/live-dev-server.js
+++ b/src/write/build-modes/live-dev-server.js
@@ -1,8 +1,6 @@
 import * as http from 'node:http';
-import {createReadStream} from 'node:fs';
-import {stat} from 'node:fs/promises';
+import {readFile, stat} from 'node:fs/promises';
 import * as path from 'node:path';
-import {pipeline} from 'node:stream/promises'
 
 import {logInfo, logWarn, progressCallAll} from '#cli';
 import {watchContentDependencies} from '#content-dependencies';
@@ -10,11 +8,9 @@ import {quickEvaluate} from '#content-function';
 import * as html from '#html';
 import * as pageSpecs from '#page-specs';
 import {serializeThings} from '#serialize';
-import {empty} from '#sugar';
 
 import {
   getPagePathname,
-  getPagePathnameAcrossLanguages,
   getURLsFrom,
   getURLsFromRoot,
 } from '#urls';
@@ -44,8 +40,8 @@ export function getCLIOptions() {
       },
     },
 
-    'quiet-responses': {
-      help: `Disables outputting [200] and [404] responses in the server log`,
+    'loud-responses': {
+      help: `Enables outputting [200] and [404] responses in the server log, which are suppressed by default`,
       type: 'flag',
     },
   };
@@ -58,14 +54,16 @@ export async function go({
 
   defaultLanguage,
   languages,
+  missingImagePaths,
   srcRootPath,
+  thumbsCache,
   urls,
   wikiData,
 
   cachebust,
   developersComment,
   getSizeOfAdditionalFile,
-  getSizeOfImageFile,
+  getSizeOfImagePath,
   niceShowAggregate,
 }) {
   const showError = (error) => {
@@ -78,7 +76,7 @@ export async function go({
 
   const host = cliOptions['host'] ?? defaultHost;
   const port = parseInt(cliOptions['port'] ?? defaultPort);
-  const quietResponses = cliOptions['quiet-responses'] ?? false;
+  const loudResponses = cliOptions['loud-responses'] ?? false;
 
   const contentDependenciesWatcher = await watchContentDependencies();
   const {contentDependencies} = contentDependenciesWatcher;
@@ -160,10 +158,10 @@ export async function go({
         });
         response.writeHead(200, contentTypeJSON);
         response.end(json);
-        if (!quietResponses) console.log(`${requestHead} [200] /data.json`);
+        if (loudResponses) console.log(`${requestHead} [200] /data.json`);
       } catch (error) {
         response.writeHead(500, contentTypeJSON);
-        response.end({error: `Internal error serializing wiki JSON`});
+        response.end(`Internal error serializing wiki JSON`);
         console.error(`${requestHead} [500] /data.json`);
         showError(error);
       }
@@ -224,7 +222,7 @@ export async function go({
         'gif': 'image/gif',
         'ico': 'image/vnd.microsoft.icon',
         'jpg': 'image/jpeg',
-        'jpeg:': 'image/jpeg',
+        'jpeg': 'image/jpeg',
         'js': 'text/javascript',
         'mjs': 'text/javascript',
         'mp3': 'audio/mpeg',
@@ -249,14 +247,13 @@ export async function go({
 
       try {
         const {size} = await stat(filePath);
+        const buffer = await readFile(filePath)
         response.writeHead(200, contentType ? {
           'Content-Type': contentType,
           'Content-Length': size,
         } : {});
-        await pipeline(
-          createReadStream(filePath),
-          response);
-        if (!quietResponses) console.log(`${requestHead} [200] ${pathname}`);
+        response.end(buffer);
+        if (loudResponses) console.log(`${requestHead} [200] ${pathname}`);
       } catch (error) {
         response.writeHead(500, contentTypePlain);
         response.end(`Failed during file-to-response pipeline`);
@@ -274,7 +271,7 @@ export async function go({
     if (!Object.hasOwn(urlToPageMap, pathnameKey)) {
       response.writeHead(404, contentTypePlain);
       response.end(`No page found for: ${pathnameKey}\n`);
-      if (!quietResponses) console.log(`${requestHead} [404] ${pathname}`);
+      if (loudResponses) console.log(`${requestHead} [404] ${pathname}`);
       return;
     }
 
@@ -331,22 +328,17 @@ export async function go({
         return;
       }
 
-      const localizedPathnames = getPagePathnameAcrossLanguages({
-        defaultLanguage,
-        languages,
-        pagePath: servePath,
-        urls,
-      });
-
       const bound = bindUtilities({
         absoluteTo,
         cachebust,
         defaultLanguage,
         getSizeOfAdditionalFile,
-        getSizeOfImageFile,
+        getSizeOfImagePath,
         language,
         languages,
+        missingImagePaths,
         pagePath: servePath,
+        thumbsCache,
         to,
         urls,
         wikiData,
@@ -363,14 +355,14 @@ export async function go({
 
       const {pageHTML} = html.resolve(topLevelResult);
 
-      if (!quietResponses) console.log(`${requestHead} [200] ${pathname}`);
+      if (loudResponses) console.log(`${requestHead} [200] ${pathname}`);
       response.writeHead(200, contentTypeHTML);
       response.end(pageHTML);
     } catch (error) {
-      response.writeHead(500, contentTypePlain);
-      response.end(`Error generating page, view server log for details\n`);
       console.error(`${requestHead} [500] ${pathname}`);
       showError(error);
+      response.writeHead(500, contentTypePlain);
+      response.end(`Error generating page, view server log for details\n`);
     }
   });
 
@@ -393,8 +385,11 @@ export async function go({
   server.on('listening', () => {
     logInfo`${'All done!'} Listening at: ${address}`;
     logInfo`Press ^C here (control+C) to stop the server and exit.`;
-    if (quietResponses) {
-      logInfo`Suppressing [200] and [404] response logging.`;
+    if (loudResponses) {
+      logInfo`Printing [200] and [404] responses.`
+    } else {
+      logInfo`Suppressing [200] and [404] response logging.`
+      logInfo`(Pass --loud-responses to show these.)`;
     }
   });
 
diff --git a/src/write/build-modes/static-build.js b/src/write/build-modes/static-build.js
index 2210dfe7..09316999 100644
--- a/src/write/build-modes/static-build.js
+++ b/src/write/build-modes/static-build.js
@@ -17,16 +17,15 @@ import {serializeThings} from '#serialize';
 import {empty, queue, withEntries} from '#sugar';
 
 import {
+  fileIssue,
   logError,
   logInfo,
   logWarn,
-  progressCallAll,
   progressPromiseAll,
 } from '#cli';
 
 import {
   getPagePathname,
-  getPagePathnameAcrossLanguages,
   getURLsFrom,
   getURLsFromRoot,
 } from '#urls';
@@ -89,15 +88,17 @@ export async function go({
 
   defaultLanguage,
   languages,
+  missingImagePaths,
   srcRootPath,
+  thumbsCache,
   urls,
-  urlSpec,
   wikiData,
 
   cachebust,
   developersComment,
   getSizeOfAdditionalFile,
-  getSizeOfImageFile,
+  getSizeOfImagePath,
+  niceShowAggregate,
 }) {
   const outputPath = cliOptions['out-path'] || process.env.HSMUSIC_OUT;
   const appendIndexHTML = cliOptions['append-index-html'] ?? false;
@@ -253,6 +254,8 @@ export async function go({
   ));
   */
 
+  let errored = false;
+
   const contentDependencies = await quickLoadContentDependencies();
 
   const perLanguageFn = async (language, i, entries) => {
@@ -265,13 +268,6 @@ export async function go({
       ...pageWrites.map(page => () => {
         const pagePath = page.path;
 
-        const localizedPathnames = getPagePathnameAcrossLanguages({
-          defaultLanguage,
-          languages,
-          pagePath,
-          urls,
-        });
-
         const pathname = getPagePathname({
           baseDirectory,
           pagePath,
@@ -294,23 +290,33 @@ export async function go({
           cachebust,
           defaultLanguage,
           getSizeOfAdditionalFile,
-          getSizeOfImageFile,
+          getSizeOfImagePath,
           language,
           languages,
+          missingImagePaths,
           pagePath,
+          thumbsCache,
           to,
           urls,
           wikiData,
         });
 
-        const topLevelResult =
-          quickEvaluate({
-            contentDependencies,
-            extraDependencies: {...bound, appendIndexHTML},
-
-            name: page.contentFunction.name,
-            args: page.contentFunction.args ?? [],
-          });
+        let topLevelResult;
+        try {
+          topLevelResult =
+            quickEvaluate({
+              contentDependencies,
+              extraDependencies: {...bound, appendIndexHTML},
+
+              name: page.contentFunction.name,
+              args: page.contentFunction.args ?? [],
+            });
+        } catch (error) {
+          logError`\rError generating page: ${pathname}`;
+          niceShowAggregate(error);
+          errored = true;
+          return;
+        }
 
         const {pageHTML, oEmbedJSON} = html.resolve(topLevelResult);
 
@@ -358,6 +364,16 @@ export async function go({
 
   // The single most important step.
   logInfo`Written!`;
+
+  if (errored) {
+    logWarn`The code generating content for some pages ended up erroring.`;
+    logWarn`These pages were skipped, so if you ran a build previously and`;
+    logWarn`they didn't error that time, then the old version is still`;
+    logWarn`available - albeit possibly outdated! Please scroll up and send`;
+    logWarn`the HSMusic developers a copy of the errors:`;
+    fileIssue({topMessage: null});
+  }
+
   return true;
 }
 
@@ -454,14 +470,9 @@ async function writeFavicon({
 }
 
 async function writeSharedFilesAndPages({
-  language,
   outputPath,
-  urls,
-  wikiData,
   wikiDataJSON,
 }) {
-  const {groupData, wikiInfo} = wikiData;
-
   return progressPromiseAll(`Writing files & pages shared across languages.`, [
     wikiDataJSON &&
       writeFile(