docs: formally document how admonitions can be customized (facebook#7799

)

website/docs/guides/markdown-features/markdown-features-admonitions.mdx

@@ -11,7 +11,7 @@ import Tabs from '@theme/Tabs';
 import TabItem from '@theme/TabItem';
 import Admonition from '@theme/Admonition';
 
-In addition to the basic Markdown syntax, we use [remark-admonitions](https://github.com/elviswolcott/remark-admonitions) alongside MDX to add support for admonitions. Admonitions are wrapped by a set of 3 colons.
+In addition to the basic Markdown syntax, we have a special admonitions syntax by wrapping text with a set of 3 colons, followed by a label denoting its type.
 
 Example:
 
@@ -107,7 +107,7 @@ Hello world
 
 ## Specifying title {#specifying-title}
 
-You may also specify an optional title
+You may also specify an optional title.
 
 ```md
 :::note Your Title
@@ -204,3 +204,53 @@ The types that are accepted are the same as above: `note`, `tip`, `danger`, `inf
   </Admonition>
 </BrowserWindow>
 ```
+
+## Customizing admonitions {#customizing-admonitions}
+
+There are two kinds of customizations possible with admonitions: **parsing** and **rendering**.
+
+### Customizing rendering behavior {#customizing-rendering-behavior}
+
+You can customize how each individual admonition type is rendered through [swizzling](../../swizzling.md). You can often achieve your goal through a simple wrapper. For example, in the follow example, we swap out the icon for `info` admonitions only.
+
+```jsx title="src/theme/Admonition.js"
+import React from 'react';
+import Admonition from '@theme-original/Admonition';
+import MyIcon from '@site/static/img/info.svg';
+
+export default function AdmonitionWrapper(props) {
+  if (props.type !== 'info') {
+    return <Admonition {...props} />;
+  }
+  return <Admonition icon={<MyIcon />} {...props} />;
+}
+```
+
+### Customizing parsing behavior {#customizing-parsing-behavior}
+
+Admonitions are implemented with a [Remark plugin](./markdown-features-plugins.mdx). The plugin is designed to be configurable. To customize the Remark plugin for a specific content plugin (docs, blog, pages), pass the options through the `admonitions` key.
+
+```js title="docusaurus.config.js"
+module.exports = {
+  presets: [
+    [
+      '@docusaurus/preset-classic',
+      {
+        docs: {
+          admonitions: {
+            tag: ':::',
+            keywords: ['note', 'tip', 'info', 'caution', 'danger'],
+          },
+        },
+      },
+    ],
+  ],
+};
+```
+
+The plugin accepts two options:
+
+- `tag`: The tag that encloses the admonition. Defaults to `:::`.
+- `keywords`: An array of keywords that can be used as the type for the admonition. Note that if you override this, the default values will not be applied.
+
+The `keyword` will be passed as the `type` prop of the `Admonition` component. If you register more types than the default, you are also responsible for providing their implementation—including the container's style, icon, default title text, etc. You would usually need to [eject](../../swizzling.md#ejecting) the `@theme/Admonition` component, so you could re-use the same infrastructure as the other types.

website/docs/guides/markdown-features/markdown-features-plugins.mdx

@@ -25,7 +25,7 @@ If you play with the [MDX playground](https://mdx-git-renovate-babel-monorepo-md
 
 :::tip
 
-Use plugins to introduce shorter syntax for the most commonly used JSX elements in your project. The [admonition](./markdown-features-admonitions.mdx) syntax that we offer is also generated by a [Remark plugin](https://github.com/elviswolcott/remark-admonitions), and you could do the same for your own use case.
+Use plugins to introduce shorter syntax for the most commonly used JSX elements in your project. The [admonition](./markdown-features-admonitions.mdx) syntax that we offer is also generated by a Remark plugin, and you could do the same for your own use case.
 
 :::
 

website/docs/using-plugins.md

@@ -180,26 +180,6 @@ module.exports = {
 };
 ```
 
-In addition to these plugins and themes, `@docusaurus/theme-classic` adds [`remark-admonitions`](https://github.com/elviswolcott/remark-admonitions) as a remark plugin to `@docusaurus/plugin-content-blog` and `@docusaurus/plugin-content-docs`.
-
-The `admonitions` key will be passed as the [options](https://github.com/elviswolcott/remark-admonitions#options) to `remark-admonitions`. Passing `false` will prevent the plugin from being added to MDX.
-
-```js title="docusaurus.config.js"
-module.exports = {
-  presets: [
-    [
-      '@docusaurus/preset-classic',
-      {
-        docs: {
-          // options for remark-admonitions
-          admonitions: {},
-        },
-      },
-    ],
-  ],
-};
-```
-
 ### Installing presets {#installing-presets}
 
 A preset is usually an npm package, so you install them like other npm packages using npm.