[css-anchor-position-1] Add clip-path to anchors-visible check and tie to IntersectionObserver w3c#12732

Author: fantasai

css-anchor-position-1/Overview.bs

@@ -2220,8 +2220,10 @@ depending on some commonly needed layout conditions.
 	is fully clipped by a box
 	which is an ancestor of |anchor|
 	but a descendant of |abspos|'s containing block.
-	Clipping in this case refers only to clipping due to 'overflow',
-	or other effects (such as [=paint containment=])
+	Clipping in this case refers only to the same clipping effects
+	that are (by default) checked by {{IntersectionObserver}},
+	i.e. clipping due to 'clip-path',
+	'overflow', or other effects (such as [=paint containment=])
 	that clip to the [=overflow clip edge=].
 
 	ISSUE(12732): Define timing of visibility checks.
@@ -2631,5 +2633,7 @@ Significant changes since the <a href="https://www.w3.org/TR/2025/WD-css-anchor-
 	(<a href="https://github.com/w3c/csswg-drafts/issues/12952">Issue 12952</a>)
 * Clarify that ''flip-block'', ''flip-inline'', and ''flip-start'' use the [=writing mode=] of the [=containing block=].
 	(<a href="https://github.com/w3c/csswg-drafts/issues/12869">Issue 12869</a>)
+* Add 'clip-path' to the list of clipping effects considered for ''anchors-visible''.
+	(<a href="https://github.com/w3c/csswg-drafts/issues/12732">Issue 12732</a>)
 
 See also <a href="https://www.w3.org/TR/2025/WD-css-anchor-position-1-20251007/#changes">Previous Changes</a>.