[docs] Document available Metadata (MDL-81084)

docs/devupdate.md

@@ -607,6 +607,16 @@ Here you can find all the functionality that has been deprecated in PHPUnit 9.x
 - `PHPUnit\Framework\TestCase::getMockClass()` has been deprecated, will be removed with PHPUnit 10. No clear alternative exists and won't be investigated, because there aren't cases in core.
 - Cannot use the `Test` suffix on abstract test case classes anymore. Proceed to rename them to end with `TestCase` instead.
 
+## Developer metadata
+
+<Since version="4.4" issueNumber="MDL-81084" />
+
+The list of plugins which are shipped with Moodle core is now available in a JSON format and located at `/lib/plugins.json`.
+
+The schema for this format can be found at `/lib/plugins.schema.json`.
+
+See [Developer metadata](/general/development/tools/metadata) for more information on available metadata.
+
 ## Previous versions
 
 - [Moodle 4.3 developer update](/docs/4.3/devupdate)

general/development/tools/metadata/index.md

@@ -0,0 +1,167 @@
+---
+title: Metadata
+tags:
+- apis.json
+- components.json
+- plugins.json
+- subplugins.json
+---
+
+Moodle provides a variety of metadata which is used internally by Moodle, but which may also be useful in some developer tooling and integrations.
+
+import {
+    Since,
+} from '@site/src/components';
+
+## Plugin types and subsystems
+
+The name and location on disk of every plugin type, and subsystem is described in [`lib/components.json`](https://github.com/moodle/moodle/blob/main/lib/components.json).
+
+<details>
+    <summary>Excerpt from `lib/components.json`</summary>
+
+```json
+{
+    "plugintypes": {
+        "antivirus": "lib/antivirus",
+        "availability": "availability/condition",
+        "qtype": "question/type",
+        "mod": "mod",
+        // ...
+    },
+    "subsystems": {
+        "access": null,
+        "admin": "admin",
+        // ...
+    }
+}
+```
+
+</details>
+
+## Subplugins
+
+Any plugin which implements a subplugin must describe its subplugins by name and path in that plugins `db/subplugins.json` location.
+
+<details>
+    <summary>Example of a `db/subplugins.json`</summary>
+
+```json title="mod/quiz/db/subplugins.json"
+{
+    "plugintypes": {
+        "quiz": "mod/quiz/report",
+        "quizaccess": "mod/quiz/accessrule"
+    }
+}
+```
+
+</details>
+
+## APIs
+
+<Since version="4.2" issueNumber="MDL-71096" />
+
+As described in the [Namespacing section of the coding style](../../policies/codingstyle/index.md#rules-for-level2), all Level 2 namespaces must be a Core API, or the word `local`.
+
+Only those APIs meeting the following criterion are supported for this purpose:
+
+- defined in [`/lib/apis.json`](https://github.com/moodle/moodle/blob/main/lib/apis.json); and
+- having the `allowedlevel2` flag set; and
+- either:
+  - having the same `component` as the API; or
+  - having the `allowedspread` flag set.
+
+<details>
+    <summary>Excerpt from `lib/apis.json`</summary>
+
+```json
+{
+    "access": {
+        "component": "core_access",
+        "allowedlevel2": true,
+        "allowedspread": false
+    },
+    "admin": {
+        "component": "core_admin",
+        "allowedlevel2": false,
+        "allowedspread": false
+    },
+    "adminpresets": {
+        "component": "core_adminpresets",
+        "allowedlevel2": true,
+        "allowedspread": false
+    },
+    "analytics": {
+        "component": "core_analytics",
+        "allowedlevel2": true,
+        "allowedspread": true
+    },
+    // ...
+}
+```
+
+</details>
+
+:::tip
+
+A JSON schema for this file can be found at [`/lib/apis.schema.json`](https://github.com/moodle/moodle/blob/main/lib/apis.schema.json).
+
+:::
+
+## Standard Plugins
+
+<Since version="4.4" issueNumber="MDL-81084" />
+
+A list of the plugins which are shipped a standard Moodle installation, as well as the plugins which have recently been removed from this list is available in [`lib/plugins.json`](https://github.com/moodle/moodle/blob/main/lib/plugins.json).
+
+This list is in categorised under the categories `standard`, and `deleted`, and then by the plugin type, and finally the plugin name.
+
+<details>
+    <summary>Excerpt from `lib/plugins.json`</summary>
+
+```json
+{
+    "standard": {
+        "antivirus": [
+            "clamav"
+        ],
+        "assignfeedback": [
+            "comments",
+            "editpdf",
+            "file",
+            "offline"
+        ],
+        "assignsubmission": [
+            "comments",
+            "file",
+            "onlinetext"
+        ],
+        // ...
+    },
+    "deleted": {
+        "assignment": [
+            "offline",
+            "online",
+            "upload",
+            "uploadsingle"
+        ],
+        "auth": [
+            "fc",
+            "imap",
+            "nntp",
+            "pam",
+            "pop3",
+            "radius"
+        ],
+        // ...
+    }
+}
+```
+
+</details>
+
+:::tip
+
+A JSON schema for this file can be found at [`/lib/plugins.schema.json`](https://github.com/moodle/moodle/blob/main/lib/plugins.schema.json).
+
+:::