feat: new 500.astro error prop

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

@@ -96,10 +96,52 @@ 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 to show for pages in your `hybrid` or `server` project that are [rendered on demand](/en/guides/server-side-rendering/#enable-on-demand-server-rendering), create the file `src/pages/500.astro`. This custom page is not available for prerendered pages.
+
+If an error occurs rendering this page, your host's default 500 error page will be shown to your visitor.
+
+### Use the `error` prop
+
+<p><Since v="4.10.0" /></p>
+
+`500.astro` accepts an `error` 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>
+```
+
+### Enable in development mode
+
+<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'`. This value can be included in a `.env` file:
+
+```ini title=".env"
+ASTRO_CUSTOM_500=true
+```
+
+It is also possible to use the CLI  to set this environment variable:
+
+```sh
+ASTRO_CUSTOM_500=true astro dev
+```
+
+If an error occurs when rendering this custom page in development mode, Astro's default error overlay will be shown instead.
+
 ## Page Partials
 
 <p><Since v="3.4.0" /></p>