[css-contain-2] Stop monkey-patching the HTML spec.

Author: emilio

css-contain-2/Overview.bs

@@ -1994,6 +1994,18 @@ Suppressing An Element's Contents Entirely: the 'content-visibility' property {#
 		When the element becomes disconnected, the element's [=proximity to the viewport=] becomes [=not determined=].
 	</div>
 
+	<div>
+		All elements have a <dfn>currently relevant to the user</dfn> flag, initially false.
+	</div>
+
+	<div algorithm="update content relevancy for a document">
+		To <dfn export>update content relevancy for a document</dfn> <var>doc</var>:
+
+		1. For each <var>element</var> [=connected=] to doc with ''auto'' used value of ''content-visibility''
+			1. If <var>element</var> is [=relevant to the user=], then set <var>element</var>'s [=currently relevant to the user=] flag to true.
+			1. Otherwise, set <var>element</var>'s [=currently relevant to the user=] flag to false.
+	</div>
+
 	<div algorithm>
 		An element is <dfn export>relevant to the user</dfn>
 		if <strong>any</strong> of the following conditions are true:
@@ -2308,14 +2320,7 @@ Restrictions and Clarifications {#cv-notes}
 	</wpt>
 
 3. If an element starts or stops [=skipped contents|skipping its contents=],
-	this change happens
-	after the requestAnimationFrame callbacks
-	of the frame that renders the effects of the change
-	have run.
-	Specifically, such changes will take effect between steps 13 and 14
-	of [=update the rendering=] step of the Processing Model
-	(between “run the animation frame callbacks”
-	and “run the update intersection observations steps”).
+	this change happens when [=update content relevancy for a document=] runs.
 
 	<div class=note>
 		Determining the viewport intersection of the element