[css-anchor-position] Make strongly-hidden elements also trigger hiding of things depending on them. w3c#7758

Author: tabatkins

css-anchor-position-1/Overview.bs

@@ -1091,6 +1091,26 @@ where this could be the case.
 	Issue: Make sure this definition of clipped
 	is consistent with View Transitions,
 	which wants a similar concept.
+
+	|anchor| is also considered [=clipped by intervening elements=]
+	if it is [=strongly hidden=]
+	by 'position-visibility'.
+
+	Note: This ensures that in a "chained anchor" situation,
+	if the first abspos is hidden due to this property
+	(due to its anchor being scrolled off),
+	then another abspos using it as an anchor will also be hidden,
+	rather than <em>also</em> floating in a nonsensical location.
+
+	Issue: I think we don't want to make this dependent
+	on any <em>other</em> types of invisibility.
+	Anchoring an ''opacity: 0'' element
+	might make sense, for example.
+	This property's hiding is based on dynamic state,
+	which you can't otherwise select on;
+	all of those other sources are caused by other styling,
+	which you can just condition this element on as well
+	if you want to hide it at the same time.
 </div>
 
 Making an element <dfn noexport>strongly hidden</dfn>