Repository: vercel/next.js
Pull request: Update documentation to explain behavior in a Catch-all route

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Changed files:
filename: docs/01-app/03-api-reference/04-functions/use-selected-layout-segment.mdx
patch: @@ -35,6 +35,7 @@ export default function ExampleClientComponent() {
 >
 > - Since `useSelectedLayoutSegment` is a [Client Component](/docs/app/getting-started/server-and-client-components) hook, and Layouts are [Server Components](/docs/app/getting-started/server-and-client-components) by default, `useSelectedLayoutSegment` is usually called via a Client Component that is imported into a Layout.
 > - `useSelectedLayoutSegment` only returns the segment one level down. To return all active segments, see [`useSelectedLayoutSegments`](/docs/app/api-reference/functions/use-selected-layout-segments)
+> - For [catch-all](/docs/app/api-reference/file-conventions/dynamic-routes#catch-all-segments) routes, the matched segments are returned as a single joined string. For example, given `app/blog/[...slug]/page.js`, calling from `app/blog/layout.js` when visiting `/blog/a/b/c` returns `'a/b/c'`.
 
 ## Parameters
 
@@ -59,6 +60,12 @@ For example, given the Layouts and URLs below, the returned segment would be:
 | `app/dashboard/layout.js` | `/dashboard/analytics`         | `'analytics'`    |
 | `app/dashboard/layout.js` | `/dashboard/analytics/monthly` | `'analytics'`    |
 
+For catch-all routes (`[...slug]`), the returned segment contains all matched path segments joined as a single string:
+
+| Layout               | Visited URL   | Returned Segment |
+| -------------------- | ------------- | ---------------- |
+| `app/blog/layout.js` | `/blog/a/b/c` | `'a/b/c'`        |
+
 ## Examples
 
 ### Creating an active link component

filename: docs/01-app/03-api-reference/04-functions/use-selected-layout-segments.mdx
patch: @@ -47,6 +47,7 @@ export default function ExampleClientComponent() {
 >
 > - Since `useSelectedLayoutSegments` is a [Client Component](/docs/app/getting-started/server-and-client-components) hook, and Layouts are [Server Components](/docs/app/getting-started/server-and-client-components) by default, `useSelectedLayoutSegments` is usually called via a Client Component that is imported into a Layout.
 > - The returned segments include [Route Groups](/docs/app/api-reference/file-conventions/route-groups), which you might not want to be included in your UI. You can use the [`filter`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter) array method to remove items that start with a bracket.
+> - For [catch-all](/docs/app/api-reference/file-conventions/dynamic-routes#catch-all-segments) routes, the matched segments are returned as a single joined string within the array. For example, given `app/blog/[...slug]/page.js`, calling from `app/layout.js` when visiting `/blog/a/b/c` returns `['blog', 'a/b/c']`, not `['blog', 'a', 'b', 'c']`.
 
 ## Parameters
 
@@ -70,6 +71,13 @@ For example, given the Layouts and URLs below, the returned segments would be:
 | `app/dashboard/layout.js` | `/dashboard`          | `[]`                        |
 | `app/dashboard/layout.js` | `/dashboard/settings` | `['settings']`              |
 
+For catch-all routes (`[...slug]`), all matched path segments are returned as a single joined string within the array:
+
+| Layout               | Visited URL   | Returned Segments   |
+| -------------------- | ------------- | ------------------- |
+| `app/layout.js`      | `/blog/a/b/c` | `['blog', 'a/b/c']` |
+| `app/blog/layout.js` | `/blog/a/b/c` | `['a/b/c']`         |
+
 ## Version History
 
 | Version   | Changes                                 |