[scroll-animations-1] Scroll timelines are inactive in paged media. w3c#8226

Author: fantasai

scroll-animations-1/Overview.bs

@@ -153,6 +153,10 @@ spec: cssom-view-1; type: dfn;
 	(i.e. the denominator in the [=timeline/current time=] formula is zero),
 	the timeline is [=inactive timeline|inactive=].
 
+	In [=paged media=],
+	[=scroll progress timelines=] that would otherwise reference the document viewport
+	are also [=inactive timeline|inactive=].
+
 ## Anonymous Scroll Progress Timelines ## {#scroll-timelines-anonymous}
 
 ### The ''scroll()'' notation ### {#scroll-notation}
@@ -210,6 +214,9 @@ spec: cssom-view-1; type: dfn;
 			then the [=scroll progress timeline=] is [=inactive timeline|inactive=].
 	</dl>
 
+	References to the [=root element=] propagate to the document viewport
+	(which functions as its [=scroll container=]).
+
 	Each use of ''scroll()'' corresponds to its own instance of {{ScrollTimeline}}
 	in the Web Animations API,
 	even if multiple elements use ''scroll()'' to refer
@@ -500,6 +507,10 @@ spec: cssom-view-1; type: dfn;
 	(i.e. the denominator in the [=timeline/current time=] formula is zero),
 	the timeline is [=inactive timeline|inactive=].
 
+	In [=paged media=],
+	[=view progress timelines=] that would otherwise reference the document viewport
+	are also [=inactive timeline|inactive=].
+
 ## Anonymous View Progress Timelines ## {#view-timelines-anonymous}
 
 ### The ''view()'' notation ### {#view-notation}
@@ -626,7 +637,8 @@ spec: cssom-view-1; type: dfn;
 
 	If the {{ScrollTimeline/source}} or {{ViewTimeline/subject}} of a {{ViewTimeline}}
 	is an element whose [=principal box=] does not exist,
-	or if its nearest ancestor [=scroll container=] has no [=scrollable overflow=],
+	or if its nearest ancestor [=scroll container=] has no [=scrollable overflow=]
+	(or if there is no such ancestor, e.g. in print media),
 	then the {{ViewTimeline}} is [=inactive timeline|inactive=].
 
 	The values of {{ViewTimeline/subject}}, {{ScrollTimeline/source}}, and {{AnimationTimeline/currentTime}}