Injected frontmatter change (withastro#2250)

Co-authored-by: Sarah Rainsberger <[email protected]>

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

@@ -341,14 +341,14 @@ const { post } = Astro.props;
 
 ## Rendering entry content
 
-Every collection entry includes a `render()` function that gives you access to the contents of the Markdown or MDX file. This includes a `<Content />` component for rendering the document body, as well as the document headings and injected frontmatter.
+Every collection entry includes a `render()` function that gives you access to the contents of the Markdown or MDX file. This includes a `<Content />` component for rendering the document body, as well as the document headings and frontmatter modified via remark or rehype.
 
 ```astro {5}
 ---
 // src/pages/render-example.astro
 import { getEntry } from 'astro:content';
 const entry = await getEntry('blog', 'post-1.md');
-const { Content, headings, injectedFrontmatter } = await entry.render();
+const { Content, headings, remarkPluginFrontmatter } = await entry.render();
 ---
 ```
 
@@ -390,23 +390,27 @@ const blogPosts = await getCollection('blog');
 })}
 ```
 
-### Access injected frontmatter from `render()`
+### Access modified frontmatter from `render()`
 
-Astro allows you to [inject frontmatter using remark or rehype plugins.](/en/guides/markdown-content/#example-injecting-frontmatter) You can access these values using the `injectedFrontmatter` property from `render()`:
+Astro allows you to [modify frontmatter using remark or rehype plugins](/en/guides/markdown-content/#modifying-frontmatter-programmatically). You can access this modified frontmatter using the `remarkPluginFrontmatter` property from `render()`:
 
-```astro "{ injectedFrontmatter }"
+```astro "{ remarkPluginFrontmatter }"
 ---
 import { getCollection } from 'astro:content';
 const blogPosts = await getCollection('blog');
 ---
 
 {blogPosts.map(async (post) => {
-  const { injectedFrontmatter } = await post.render();
-  return <p>{post.data.title} — {injectedFrontmatter.readingTime}</p>
+  const { remarkPluginFrontmatter } = await post.render();
+  return <p>{post.data.title} — {remarkPluginFrontmatter.readingTime}</p>
 })}
 ```
 
-Assuming `readingTime` was injected ([see our reading time example](/en/guides/markdown-content/#example-calculate-reading-time)), it will be available on the `injectedFrontmatter` object.
+Assuming `readingTime` was injected ([see our reading time example](/en/guides/markdown-content/#example-calculate-reading-time)), it will be available on the `remarkPluginFrontmatter` object.
+
+:::caution
+Remark and rehype plugins will have access to the _raw_ Markdown or MDX document frontmatter. This means frontmatter will not reflect any changes or defaults applied by your `schema`.
+:::
 
 <details>
 <summary>**🙋 Why don't `getCollection()` and `getEntry()` contain these values?**</summary>

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

@@ -3,9 +3,10 @@ layout: ~/layouts/MainLayout.astro
 title: Markdown & MDX
 description: Learn how to create content using Markdown or MDX with Astro
 i18nReady: true
-setup: import Since from '~/components/Since.astro'
 ---
 
+import Since from '~/components/Since.astro'
+
 [Markdown](https://daringfireball.net/projects/markdown/) is commonly used to author text-heavy content like blog posts and documentation. Astro includes built-in support for standard Markdown files. 
 
 With the [@astrojs/mdx integration](/en/guides/integrations-guide/mdx/) installed, Astro also supports [MDX](https://mdxjs.com/) (`.mdx`) files which bring added features like support for JavaScript expressions and components in your Markdown content. 
@@ -468,7 +469,7 @@ export default {
 }
 ```
 
-#### Example: Injecting frontmatter
+### Modifying frontmatter programmatically
 
 You can add frontmatter properties to all of your Markdown and MDX files by using a [remark or rehype plugin](#markdown-plugins).
 
@@ -483,6 +484,12 @@ You can add frontmatter properties to all of your Markdown and MDX files by usin
     }
     ```
 
+    :::tip
+    <Since v="2.0.0" />
+
+    `data.astro.frontmatter` contains all properties from a given Markdown or MDX document. This allows you to modify existing frontmatter properties, or compute new properties from this existing frontmatter.
+    :::
+
 2. Apply this plugin to your `markdown`  or `mdx` integration config:
 
     ```js title="astro.config.mjs" "import { exampleRemarkPlugin } from './example-remark-plugin.mjs';" "remarkPlugins: [exampleRemarkPlugin],"

src/pages/en/reference/api-reference.mdx

@@ -830,14 +830,14 @@ A function to compile a given Markdown or MDX document for rendering. This retur
 
 - `<Content />` - A component used to render the document's contents in an Astro file.
 - `headings` - A generated list of headings, [mirroring Astro's `getHeadings()` utility](/en/guides/markdown-content/#exported-properties) on Markdown and MDX imports.
-- `injectedFrontmatter ` - An object of frontmatter [injected via remark or rehype plugins](/en/guides/markdown-content/#example-injecting-frontmatter). Set to type `any`.
+- `remarkPluginFrontmatter ` - The modified frontmatter object after any [remark or rehype plugins have been applied](/en/guides/markdown-content/#modifying-frontmatter-programmatically). Set to type `any`.
 
 ```astro
 ---
 import { getEntry } from 'astro:content';
 const entry = await getEntry('blog', 'entry-1.md');
 
-const { Content, headings, injectedFrontmatter } = await entry.render();
+const { Content, headings, remarkPluginFrontmatter } = await entry.render();
 ---
 ```