Add 'scroll' to timeline-range-name options (mdn#43571)

* Add 'scroll' to timeline-range-name options

* Update files/en-us/web/css/reference/values/timeline-range-name/index.md

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

* Update files/en-us/web/css/reference/values/timeline-range-name/index.md

Co-authored-by: Hamish Willee <hamishwillee@gmail.com>

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Hamish Willee <hamishwillee@gmail.com>

Author: 3 people

files/en-us/web/css/reference/values/timeline-range-name/index.md

@@ -39,9 +39,12 @@ Valid `<timeline-range-name>` values:
 - `exit-crossing`
   - : Represents the range where the principal box crosses the start border edge. The range start (0% progress) occurs when the start border edge of the element's principal box coincides with the start edge of its view progress visibility range. The range end (100% progress) is the point at which the end border edge of the element's principal box coincides with the start edge of its view progress visibility range. The size of the range is the size of the element's principle box in the scroll direction.
 
+- `scroll`
+  - : Represents the full range of the {{glossary("scroll container")}} on which the view progress timeline is defined. The range start (0% progress) and end (100% progress) occur at the very start and end positions of the scroll container underlying the view progress timeline.
+
 ## Formal syntax
 
-{{CSSSyntaxRaw(`<timeline-range-name> = cover | contain | entry | exit | entry-crossing | exit-crossing`)}}
+{{CSSSyntaxRaw(`<timeline-range-name> = cover | contain | entry | exit | entry-crossing | exit-crossing | scroll`)}}
 
 ## Examples