[css-anchor-position] Rewrite the ordering conditions on 'acceptable anchor element' to be more explicit and hopefully clearer.

Author: tabatkins

css-anchor-position-1/Overview.bs

@@ -392,25 +392,42 @@ in anchor positioning.
 		per the effects of 'anchor-scope' on |positioned el|
 		or its ancestors.
 
-	* Either |possible anchor| is a descendant of |positioned el|'s [=containing block=],
-		or |positioned el|'s [=containing block=] is the [=initial containing block=].
-
-	* If |possible anchor| has the same [=containing block=] as |positioned el|,
-		then either |possible anchor| is not [=absolutely positioned=],
-		or |possible anchor| precedes |positioned el| in the tree order.
-
-	* If |possible anchor| has a different [=containing block=] from |positioned el|,
-		then the last [=containing block=] in |possible anchor|'s [=containing block chain=]
-		before reaching |positioned el|'s [=containing block=]
-		is either not [=absolutely positioned=]
-		or precedes |positioned el| in the tree order.
+	* |possible anchor| is painted strictly before |positioned el|,
+		aka one of the following is true:
+		* |positioned el| is [=in a higher top layer=] than |possible anchor|
+		* Both elements are [=in the same top layer=]
+			but have different [=containing blocks=], 
+			and |positioned el|'s [=containing block=]
+			is an ancestor of |possible anchor|'s [=containing block=]
+			in the [=containing block chain=],
+			aka one of the following:
+			* |positioned el|'s [=containing block=] is the viewport,
+				and |possible anchor|'s [=containing block=] isn't.
+			* |positioned el|'s [=containing block=] is the [=initial containing block=],
+				and |possible anchor|'s [=containing block=] is generated by an element,
+			* both elements' [=containing blocks=] are generated by elements,
+				and |positioned el|'s containing block
+				is an ancestor in the [=flat tree=]
+				to that of |possible anchor|'s [=containing block=].
+		* Both elements are [=in the same top layer=]
+			and have the same [=containing block=],
+			and are both [=absolutely positioned=],
+			and |possible anchor| is earlier in [=flat tree=] order
+			than |positioned el|.
+		* Both elements are [=in the same top layer=]
+			and have the same [=containing block=],
+			but |possible anchor| isn't [=absolutely positioned=].
 
 	* If |possible anchor| is in the [=skipped contents=] of another element,
 		then |positioned el| is in the [=skipped contents=] of that same element.
 
 		Note: In other words, |positioned el| can anchor to |possible anchor| 
 		if they're both in the same skipped "leaf",
 		but it can't anchor "across" leafs.
+		This means skipping an element that contains both of them
+		won't suddenly cause the |positioned el| to move to another anchor,
+		but still prevents positioned elements <em>elsewhere</em> in the page
+		from anchoring to the skipped element.
 </div>
 
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