[css-anchor-position] Specify the timing of 'clipped by intervening boxes'. #12732

Author: tabatkins

css-anchor-position-1/Overview.bs

@@ -1259,6 +1259,9 @@ depending on some commonly needed layout conditions.
 	or other effects (such as [=paint containment=])
 	that clip to the [=overflow clip edge=].
 
+	Whether or not |anchor| is [=clipped by intervening boxes=]
+	is determined immediately prior to triggering {{ResizeObserver}}s.
+
 	Note: This means that if an abspos is next to its anchor in the DOM,
 	for example,
 	it'll remain visible even if its default anchor is scrolled off,