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

css-contain-2/Overview.bs

@@ -1994,6 +1994,45 @@ 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 currently relevant to the user">
+		To <dfn>update currently relevant to the user</dfn> given an element <var>element</var>:
+
+		1. Let <var>currentlyRelevant</var> be true if <var>element</var> is [=relevant to the user=], otherwise false.
+		1. If <var>element</var>'s [=currently relevant to the user=] flag is equal to <var>currentlyRelevant</var>, then return false.
+		1. Set <var>element</var>'s [=currently relevant to the user=] flag to <var>currentlyRelevant</var>.
+		1. return true.
+	</div>
+
+	<div algorithm="update content relevancy for a document">
+		To <dfn export>update content relevancy for a document</dfn> given a document <var>doc</var>, and a boolean <var>updateNonInitial</var>:
+
+		1. Let <var>changed</var> be false.
+		1. For each <var>element</var> [=connected=] to doc with ''auto'' used value of ''content-visibility'':
+			1. If <var>updateNonInitial</var> is true:
+				1. If [=update currently relevant to the user=] for <var>element</var> returns true.
+					1. Set <var>changed</var> to true.
+			1. Let <var>isInitialDetermination</var> be true if <var>element</var>'s [=proximity to the viewport=] is [=not determined=], otherwise false.
+			1. Determine [=proximity to the viewport=] for <var>element</var>.
+			1. If <var>isInitialDetermination</var> is false, then [=continue=].
+			1. If [=update currently relevant to the user=] for <var>element</var> returns true.
+				1. Set <var>changed</var> to true.
+		1. return <var>changed</var>.
+
+		<div class=note>
+		The intent of the <var>changed</var> and <var>updateNonInitial</var>
+		variables is for the initial viewport proximity determination, which takes
+		effect immediately, to be reflected in the style and layout calculation
+		this frame.
+
+		Proximity determinations other than the initial one take effect
+		at the next rendering opportunity.
+		</div>
+	</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 +2347,7 @@ 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