Merge branch 'preview' into listing-tweaks

65 files changed, 2659 insertions, 0 deletions

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)),
+    },
+  };
+}