[css-anchor-position-1] Clarify when last successful position is cleared. #12577

Author: fantasai

css-anchor-position-1/Overview.bs

@@ -2141,12 +2141,15 @@ laying out later boxes cannot change this decision.
 		that it's currently using.
 
 	* Otherwise, if |el| has a [=last successful position option=]
-		and if any of the following are true of it,
-		remove its [=last successful position option=]:
-
-		* |el| is not [=absolutely positioned=]
-		* |el|'s computed value for 'position-try-fallbacks' has changed
-		* Any of the ''@position-try'' rules referenced by |el|'s 'position-try-fallbacks'
+		remove its [=last successful position option=]
+		if any of the following are true:
+
+		* its computed 'position' value has changed,
+			its [=containing block=] has changed,
+			or it no longer generates a box
+		* its computed value for any [=longhand property|longhand=] of 'position-try' has changed
+		* its computed value for any [=@position-try property=] has changed
+		* Any of the ''@position-try'' rules referenced by it
 			have been added, removed, or mutated.
 
 		Then, [=determine position fallback styles=] for |el|