[css-anchor-position-1] Clarify which clipping position-visibility cares about

Author: fantasai

css-anchor-position-1/Overview.bs

@@ -1242,9 +1242,9 @@ 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.
-	This "clipping" can be due to the ancestor being a [=scroll container=],
-	or being clipped to its [=overflow clip edge=]
-	(such as by ''overflow: clip'' or [=paint containment=]).
+	Clipping in this case refers only to clipping due to 'overflow',
+	or other effects (such as [=paint containment=])
+	that clip to the [=overflow clip edge=].
 
 	Note: This means that if an abspos is next to its anchor in the DOM,
 	for example,