[css-contain-2] More refined approach, I think.

Author: emilio

css-contain-2/Overview.bs

@@ -1999,11 +1999,30 @@ Suppressing An Element's Contents Entirely: the 'content-visibility' property {#
 	</div>
 
 	<div algorithm="update content relevancy for a document">
-		To <dfn export>update content relevancy for a document</dfn> <var>doc</var>:
+		To <dfn export>update content relevancy for a document</dfn> given a document <var>doc</var>, and a boolean <var>isFirstIteration</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>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.
+			1. Determine proximity to the viewport for <var>element</var>.
+			1. If <var>element</var> is not [=currently relevant to the user=] and <var>element</var> is [=relevant to the user=], then:
+				2. Set <var>changed</var> to true.
+				2. Set <var>element</var>'s [=currently relevant to the user=] flag to true.
+			1. If <var>isFirstIteration</var> is false, then [=continue=].
+			1. If <var>element</var> is [=relevant to the user=], then:
+				1. If <var>element</var>'s [=currently relevant to the user=] flag is false, set <var>changed</var> to true.
+				1. Set <var>element</var>'s [=currently relevant to the user=] flag to true.
+			1. Otherwise:
+				1. If <var>element</var>'s [=currently relevant to the user=] flag is true, set <var>changed</var> to true.
+				1. Set <var>element</var>'s [=currently relevant to the user=] flag to false.
+		1. return <var>changed</var>.
+
+		<div class=note>
+		The intent of the <var>changed</var> variable is for the initial viewport
+		proximity determination, which takes effect immediately, to be reflected in
+		the style and layout calculation which is carried out in a previous step of
+		this loop. Proximity determinations other than the initial one take effect
+		at the next rendering opportunity.
+		</div>
 	</div>
 
 	<div algorithm>