[css-contain-2] non-local filters, and relevance to the user

Closes w3c#7711

Author: frivoal

css-contain-2/Overview.bs

@@ -1603,6 +1603,12 @@ Suppressing An Element's Contents Entirely: the 'content-visibility' property {#
 			to begin preparing for an element to be in the viewport soon.
 			A margin of 50% is suggested as a reasonable default.
 
+			If a filter (see [[FILTER-EFFECTS-1]]) with non local effects includes the element as part of its input,
+			the user agent should also treat the element as relevant to the user
+			when the filter's output can affect the rendering within the viewport
+			(or within the user-agent defined margin around the viewport),
+			even if the element itself is still off-screen.
+
 		* Either the element or its [=contents=]
 			are focused,
 			as described in the <a href="https://html.spec.whatwg.org/multipage/interaction.html#focus">focus</a> section of the HTML spec.