Update Markdown content docs for config rework

src/pages/en/guides/markdown-content.mdx

@@ -421,7 +421,7 @@ Custom components defined and exported in an MDX file must be imported and then
 
 Markdown support in Astro is powered by [remark](https://remark.js.org/), a powerful parsing and processing tool with an active ecosystem. Other Markdown parsers like Pandoc and markdown-it are not currently supported.
 
-Astro applies the [GitHub-flavored Markdown](https://github.com/remarkjs/remark-gfm) and [Smartypants](https://github.com/silvenon/remark-smartypants) plugins by default. This brings some niceties like generating clickable links from text and formatting quotes for readability. 
+Astro applies the [GitHub-flavored Markdown](https://github.com/remarkjs/remark-gfm) plugin by default. This brings some niceties like generating clickable links from text.
 
 You can customize how remark parses your Markdown in `astro.config.mjs`. See the full list of [Markdown configuration options](/en/reference/configuration-reference/#markdown-options).
 
@@ -431,12 +431,6 @@ Astro supports adding third-party [remark](https://github.com/remarkjs/remark) a
 
 We encourage you to browse [awesome-remark](https://github.com/remarkjs/awesome-remark) and [awesome-rehype](https://github.com/rehypejs/awesome-rehype) for popular plugins! See each plugin's own README for specific installation instructions.
 
-:::tip
-When adding your own plugins, Astro's default plugins are removed. You can preserve these defaults with the [`markdown.extendDefaultPlugins` flag](/en/reference/configuration-reference/#markdownextenddefaultplugins).
-:::
-
-By default, Astro's MDX integration inherits all remark and rehype plugins from your Astro config `markdown` options. To change this behavior, configure [`extendPlugins`](/en/guides/integrations-guide/mdx/#extendplugins) in your `mdx` integration.
-
 Any additional plugins you apply in your MDX config will be applied *after* your configured Markdown plugins, and will apply only to `.mdx` files. 
 
 This example applies [`remark-toc`](https://github.com/remarkjs/remark-toc) to Markdown *and* MDX, and [`rehype-accessible-emojis`](https://www.npmjs.com/package/rehype-accessible-emojis) to MDX only, while preserving Astro's default plugins:
@@ -450,8 +444,6 @@ export default {
   markdown: {
     // Applied to .md and .mdx files
     remarkPlugins: [remarkToc],
-    // Preserves remark-gfm and remark-smartypants
-    extendDefaultPlugins: true,
   },
   integrations: [mdx({
     // Applied to .mdx files only
@@ -583,6 +575,58 @@ const { minutesRead } = Astro.props.frontmatter;
 </html>
 ```
 
+### Extending Markdown config from MDX
+
+By default, Astro's MDX integration will extend [your project's existing Markdown configuration](https://docs.astro.build/en/reference/configuration-reference/#markdown-options). To override individual options, you can specify their equivalent in your MDX configuration.
+
+For example, say you need to disable GitHub-Flavored Markdown and apply a different set of remark plugins for MDX files. You can apply these options like so, with [the `extendMarkdownConfig` option](/en/guides/integrations-guide/mdx/#extendmarkdownconfig) enabled by default:
+
+```ts
+// astro.config.mjs
+import { defineConfig } from 'astro/config';
+import mdx from '@astrojs/mdx';
+
+export default defineConfig({
+  markdown: {
+    syntaxHighlight: 'prism',
+    remarkPlugins: [remarkPlugin1],
+    githubFlavoredMarkdown: true,
+  },
+  integrations: [
+    mdx({
+      // `syntaxHighlight` inherited from Markdown
+
+      // Markdown `remarkPlugins` ignored,
+      // only `remarkPlugin2` applied.
+      remarkPlugins: [remarkPlugin2],
+      // `githubFlavoredMarkdown` overridden to `false`
+      githubFlavoredMarkdown: false,
+    })
+  ]
+});
+```
+
+You may also need to disable `markdown` config extension in MDX. For this, set `extendMarkdownConfig` to `false`:
+
+```ts
+// astro.config.mjs
+import { defineConfig } from 'astro/config';
+import mdx from '@astrojs/mdx';
+
+export default defineConfig({
+  markdown: {
+    remarkPlugins: [remarkPlugin1],
+  },
+  integrations: [
+    mdx({
+      // Markdown config now ignored
+      extendMarkdownConfig: false,
+      // No `remarkPlugins` applied
+    })
+  ]
+});
+```
+
 ### Syntax Highlighting
 
 Astro comes with built-in support for [Shiki](https://shiki.matsu.io/) and [Prism](https://prismjs.com/). This provides syntax highlighting for: