feat: new 500.astro error prop

src/content/docs/en/basics/astro-pages.mdx

@@ -96,10 +96,56 @@ Files with the `.html` file extension can be placed in the `src/pages/` director
 
 ## Custom 404 Error Page
 
-For a custom 404 error page, you can create a `404.astro` or `404.md` file in `/src/pages`.
+For a custom 404 error page, you can create a `404.astro` or `404.md` file in `src/pages`.
 
 This will build to a `404.html` page. Most [deploy services](/en/guides/deploy/) will find and use it.
 
+## Custom 500 Error Page
+
+For a custom 500 error page, you can create a `500.astro` in `src/pages`.
+
+:::caution
+Once deployed, Astro will only use `500.astro` when using `output: 'hybrid'` or `output: 'server'`.
+:::
+
+If an error occur in this file, it will default to the host 500 error page.
+
+### Retrieve The Error
+
+<p><Since v="4.10.0" /></p>
+
+`500.astro` accepts an error as a prop. It can be anything so make sure to handle it properly:
+
+```astro title="src/pages/500.astro"
+---
+interface Props {
+    error: unknown
+}
+
+const { error } = Astro.props
+---
+
+<div>{error instanceof Error ? error.message : 'Unknown error'}</div>
+```
+
+### Usage In Development
+
+<p><Since v="4.10.0" /></p>
+
+You can use your custom 500 error page in development by setting the `ASTRO_CUSTOM_500` environment variable to `'true'`. For example using a `.env` file:
+
+```ini title=".env"
+ASTRO_CUSTOM_500=true
+```
+
+Or inline:
+
+```sh
+ASTRO_CUSTOM_500=true astro dev
+```
+
+If an error occur in this file, it will default to the error overlay.
+
 ## Page Partials
 
 <p><Since v="3.4.0" /></p>