[css-anchor-position] anchor() and anchor-size() resolve at *computed* time, using interleaving. w3c#8181

Author: tabatkins

css-anchor-position-1/Overview.bs

@@ -775,16 +775,9 @@ The ''anchor()'' function has three arguments:
 	specifying what the function should resolve to
 	if it's an [=invalid anchor function=].
 
-Issue: Computed value for anchor()
-probably needs to be the anchor() function,
-but with the target anchor element resolved.
-This allows for transitions to work properly
-with tree-scoped names,
-and with changing anchor elements.
-See <a href="https://github.com/w3c/csswg-drafts/issues/8180">Issue 8180</a>.
-
 An ''anchor()'' function representing a [=valid anchor function=]
-resolves at [=used value=] time
+resolves at [=computed value=] time
+(using [=style & layout interleaving=])
 to the <<length>> that would align the edge
 of the positioned elements' [=inset-modified containing block=]
 corresponding to the property the function appears in
@@ -795,6 +788,14 @@ and the positioned element's [=containing block=]
 are scrolled to their initial scroll position
 (but see [[#scroll]]).
 
+Note: This means that [=transitions=] or [=animations=]
+of a property using an [=anchor function=]
+will work "as expected" for all sorts of possible changes:
+the anchor element moving,
+anchor elements being added or removed from the document,
+the 'anchor-name' property being changed on anchors,
+etc.
+
 If the [=target anchor element=] is [=fragmented=],
 the axis-aligned bounding rectangle
 of the fragments' border boxes is used instead.
@@ -1175,7 +1176,9 @@ or the [=writing mode=] of the element's [=containing block=]
 (for ''anchor-size()/block'' and ''anchor-size()/inline'').
 
 An ''anchor-size()'' function representing a [=valid anchor-size function=]
-resolves to the <<length>> separating the relevant border edges
+resolves at [=computed value=] time
+(via [=style & layout interleaving=])
+to the <<length>> separating the relevant border edges
 (either left and right, or top and bottom,
 whichever is in the specified axis)
 of the [=target anchor element=].