[css-anchor-1] Use term to solve CB ambiguity problem w3c#12830

Author: fantasai

css-anchor-position-1/Overview.bs

@@ -425,7 +425,7 @@ in anchor positioning.
 
 	* |possible anchor| is laid out strictly before |positioned el|,
 		aka one of the following is true:
-		* |possible anchor| and |positioned el| share a [=containing block=]
+		* |possible anchor| and |positioned el| have the same [=original containing block=]
 			and either
 			* |possible anchor| is [=in a lower top layer=] than |positioned el|, or
 			* they both exist in the same [=top layer=],
@@ -435,17 +435,6 @@ in anchor positioning.
 			(if one exists)
 			is an [=acceptable anchor element=] for |positioned el|
 
-		Issue: “Share a containing block” isn't strictly correct;
-		for example, two [=absolutely positioned boxes=]
-		contained by the same [=grid container=] but with different 'grid-area' values
-		get different [=containing blocks=],
-		but should treat them as equivalent for this case.
-		On the other hand, a scroller's [=fixed containing block=]
-		and that same scroller's [=local containing block=]
-		are using different [=containing blocks=] for this purpose
-		(for example the [=initial fixed containing block=] contains the [=initial containing block=]).
-		Need a better notion of “equivalent” [=containing blocks=] here.
-
 	* If |possible anchor| is in the [=skipped contents=] of another element,
 		then |positioned el| is in the [=skipped contents=] of that same element.