docs(catalog): add the Collection type page

content/docs/(overview)/glossary.mdx

@@ -20,7 +20,7 @@ Marfa uses each word below in one sense only, in its code, its API and these doc
 | [**reverse name**](/properties-metadata-and-edges#edges) | An edge's name read from its target: `child-of` for `parent-of`. |
 | [**label**](/properties-metadata-and-edges#edges) | The heading a type or an edge type shows for itself. An edge type's label heads the source's end of an edge, such as `Children` for `parent-of`. |
 | [**reverse label**](/properties-metadata-and-edges#edges) | The heading an edge type shows for the target's end, such as `Parent`. Where an edge type names none, its label names both ends. |
-| [**collection**](/catalog/edges) | A flat container of items. An item joins one through an `in-collection` edge to an item whose type has the `container` role, such as an album. An item can be in many, a container can't itself be a member, and deleting the container leaves its members. |
+| [**collection**](/catalog/edges) | A flat container of items. An item joins one through an `in-collection` edge to an item whose type has the `container` role, such as a [`core.collection`](/catalog/collection) or an album. An item can be in many, a container can't itself be a member, and deleting the container leaves its members. |
 | [**view**](/build/save-a-view) | A saved query with one sort and one grouping, kept on the instance as a `system.view` and shared by every app. How an app draws the items is the app's own. |
 | [**file**](/files) | An item that names its bytes. |
 | [**blob**](/files) | A file's bytes, stored once under a hash of their content. |

content/docs/catalog/(types)/(core)/collection.mdx

@@ -0,0 +1,32 @@
+---
+title: Collection
+description: "Items of any type that you gather together. Members join it through the in-collection edge, and it can hold any item but another container."
+identifier: core.collection
+---
+
+<include cwd>src/generated/catalog/core.collection.md</include>
+
+## Example
+
+```json
+{
+  "type": "core.collection",
+  "properties": {
+    "title": "Kitchen renovation",
+    "description": "Quotes, sketches and the tasks still to book."
+  }
+}
+```
+
+An item joins the collection through an [`in-collection`](/catalog/edges#in-collection) edge from the item to the collection, with an optional `position`:
+
+```json
+{
+  "source_id": "01a12313-ad0e-71cd-99b4-7a176c5a9f18",
+  "target_id": "01a12314-0b52-7c41-8e0f-2d6f1a3b9c07",
+  "edge_type": "in-collection",
+  "properties": { "position": 1 }
+}
+```
+
+A container, such as another collection or an album, can't be a member. An item can be in any number of collections, and deleting a collection leaves its members in place.

content/docs/catalog/(types)/(core)/meta.json

@@ -3,6 +3,7 @@
   "defaultOpen": false,
   "pages": [
     "bookmark",
+    "collection",
     "entity",
     "event",
     "file",

src/generated/GLOSSARY.md

@@ -141,7 +141,7 @@ Access is read the same way wherever a person sees it: on the pages where they a
 | **placement**    | Where an item's file sits in a folder: its `in-folder` edge to the folder's `system.folder`, whose `path` names the file from the folder's root. It never decides what a folder holds, and it is never written in a file.                                                                                                                                                                                                                                                                                                                                                      |
 | **registry**     | The folder registry: one file on a machine listing its folders, each by its directory and the `system.folder` it follows, so each folder can find the others and a file moved or copied between two of them is told apart. It is never a folder's store, and `MARFA_FOLDER_REGISTRY` names another file in its place. The type registry is the server's catalog of types (`types.md`).                                                                                                                                                                                         |
 | **embed**        | A file an item's body shows inside it, `![](path)` or `![[file]]`: that file item's `attached-to` edge to the item, in a folder's Markdown file and in a body written through a working copy alike. In a folder, the file's `has-attachment` line lists only what the body does not embed, and an embedded file is put where the link says, any other attachment beside the document. It names a file where a file answers to it or its extension names a MIME type; anything else, `![[A note]]` say, is an embed of a note, text in the body and neither a link nor an edge. |
-| **collection**   | A container and its members: an item whose type declares the `container` role, such as an album or a series, and the items joined to it by an `in-collection` edge, each with an optional `position`. Flat: a container is never a member, `parent-of` is what hierarchy is for, and deleting the container leaves its members. Not a folder and not a view.                                                                                                                                                                                                                   |
+| **collection**   | A container and its members: an item whose type declares the `container` role, such as `core.collection`, an album or a series, and the items joined to it by an `in-collection` edge, each with an optional `position`. Flat: a container is never a member, `parent-of` is what hierarchy is for, and deleting the container leaves its members. Not a folder and not a view.                                                                                                                                                                                                |
 | **frontmatter**  | The block of `key: value` lines a Markdown file in a folder opens with between `---` fences. Its `type`, `tier`, `tags`, `state` and `occurred_at` lines are the item's own fields; `marfa_id` and `marfa_version` name the item and the version the file was written from; a line named for an edge type or a reverse name is an edge's, written in the one file at the end the type names and naming its targets as `"[[name]]"` or `"[[<id>]]"`; every other line is a property. The file's body is the property its type's `body_field` names. Never "header".             |
 
 ### Connectors

src/generated/catalog/builtin-catalog.json

@@ -64,6 +64,33 @@
     "default": "last_writer_wins"
    }
   },
+  {
+   "id": "core.collection",
+   "label": "Collection",
+   "description": "Items of any type that you gather together. Members join it through the in-collection edge, and it can hold any item but another container.",
+   "version": 0,
+   "fields": {
+    "title": {
+     "type": "string",
+     "description": "Name of the collection",
+     "required": true
+    },
+    "description": {
+     "type": "string",
+     "description": "What the collection gathers"
+    }
+   },
+   "display_hints": {
+    "title_field": "title",
+    "body_field": "description"
+   },
+   "merge_policy": {
+    "default": "last_writer_wins"
+   },
+   "roles": [
+    "container"
+   ]
+  },
   {
    "id": "core.entity",
    "label": "Entity",

src/generated/catalog/core.collection.md

@@ -0,0 +1,15 @@
+## Fields
+
+| Field         | Kind     | Required | Description                 |
+| ------------- | -------- | -------- | --------------------------- |
+| `title`       | `string` | Yes      | Name of the collection      |
+| `description` | `string` | No       | What the collection gathers |
+
+## Settings
+
+| Setting                                                | Value                              |
+| ------------------------------------------------------ | ---------------------------------- |
+| [`title_field`](/catalog/your-own-types#fields)        | `title`                            |
+| [`body_field`](/catalog/your-own-types#fields)         | `description`                      |
+| [`merge_policy`](/catalog/your-own-types#merge-policy) | `last_writer_wins` for every field |
+| [`roles`](/catalog/your-own-types#roles)               | `container`                        |