[css-scroll-snap-1] Require re-snapping to the focused element, if multiple coincide. Otherwise leave to UA. #4651

Author: fantasai

css-scroll-snap-1/Overview.bs

@@ -410,6 +410,11 @@ Re-snapping After Layout Changes</h4>
     (e.g. its associated element was not deleted),
     the scroll container must be re-snapped to that same snap position
     after the content change.
+    If multiple boxes were [=snapped=] before
+    and their [=snap positions=] no longer coincide,
+    then if one of them is focused or targetted,
+    the [=scroll container=] must re-snap to that one
+    and otherwise which one to re-snap to is UA-defined.
 
     Scrolling required by a re-snap operation to a new or different box
     must behave and animate the same way as
@@ -1216,6 +1221,21 @@ Changes Since 31 January 2019 CR {#changes-20190131}
 		<li id="change-2019-clarify-writing-mode">
 			Specified which writing mode is used to resolve 'scroll-snap-align'.
 			(<a href="https://github.com/w3c/csswg-drafts/issues/3815">Issue 3815</a>)
+		<li id="change-2019-resnap-multiple">
+			Define requirements for re-snapping when multiple elements coincide.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/4651">Issue 4651</a>)
+			<blockquote>
+				<p>If the <a>scroll container</a> was <a>snapped</a> before the content change
+				and that same <a>snap position</a> still exists
+				(e.g. its associated element was not deleted),
+				the scroll container must be re-snapped to that same snap position
+				after the content change.
+				<ins>If multiple boxes were [=snapped=] before
+				and their [=snap positions=] no longer coincide,
+				then if one of them is focused or targetted,
+				the [=scroll container=] must re-snap to that one
+				and otherwise which one to re-snap to is UA-defined.</ins></p>
+			</blockquote>
 		<li id="change-2019-resnap-animation">
 			Require re-snapping to a new element to animate the same way
 			as any other scroll-into-view operation.