[css-anchor-position-1] Use newly-defined force-hidden value for visibility hacking #10182

Author: fantasai

css-anchor-position-1/Overview.bs

@@ -1320,7 +1320,7 @@ depending on some commonly needed layout conditions.
 	::
 		If any of the box's [=required anchor references=]
 		do not resolve to a [=target anchor element=],
-		the box is [=strongly hidden=].
+		the box's 'visibility' property computes to ''force-hidden''.
 
 		Issue: What is a <dfn dfn for>required anchor reference</dfn>?
 		''anchor()'' functions that don't have a fallback value;
@@ -1335,14 +1335,14 @@ depending on some commonly needed layout conditions.
 	: <dfn>anchors-visible</dfn>
 	::
 		If the box has a [=default anchor box=]
-		but that [=anchor box=] is [=clipped by intervening boxes=],
-		this box is also [=strongly hidden=].
+		but that [=anchor box=] is [=invisible=] or [=clipped by intervening boxes=],
+		the box's 'visibility' property computes to ''force-hidden''.
 
 	: <dfn>no-overflow</dfn>
 	::
 		If the box overflows its [=inset-modified containing block=]
 		even after applying 'position-try',
-		then the box is [=strongly hidden=].
+		the box's 'visibility' property computes to ''force-hidden''.
 </dl>
 
 <div algorithm>
@@ -1366,25 +1366,13 @@ depending on some commonly needed layout conditions.
 	is consistent with View Transitions,
 	which wants a similar concept.
 
-	|anchor| is also considered [=clipped by intervening boxes=]
-	if it is [=strongly hidden=]
-	by 'position-visibility'.
-
-	Note: This ensures that in a "chained anchor" situation,
+	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.
 </div>
 
-A box that is <dfn noexport>strongly hidden</dfn>
-acts as if it
-and all of its descendants
-were ''visibility: hidden'',
-regardless of what their actual 'visibility' value is.
-(This does not affect any [=computed values=].)
-
-
 <!-- Big Text: a-size()
 
  ███▌         ███▌  ████ █████▌ █████▌   ██ ██  
@@ -1460,7 +1448,7 @@ whichever is in the specified axis)
 of the [=target anchor element=].
 
 
-<h4 id=anchor-resolution oldids=anchor-valid>
+<h4 id=anchor-size-resolution oldids=anchor-size-valid>
 Resolution of ''anchor-size()''</h4>
 
 An ''anchor-size()'' function is a