[scroll-animations-1] Define interaction with iteration count. w3c#8233

Author: fantasai

scroll-animations-1/Overview.bs

@@ -34,6 +34,9 @@ spec:web-animations-1;
 		text:active interval
 		text:start delay
 		text:end delay
+		text:active duration
+		text:iteration count
+		text:iteration duration
 spec:html;
 	type:dfn; for:/; text:browsing context
 	type:method; text:requestAnimationFrame()
@@ -672,7 +675,35 @@ spec: cssom-view-1; type: dfn;
 
 	ISSUE: Should it reset 'view-timeline-inset' also?
 
-# Named Timeline Scoping # {#timeline-scope}
+# Attaching Animations to [=Scroll-driven Timelines=] # {#scroll-driven-attachment}
+
+	Animations can be attached to [=scroll-driven timelines=]
+	using the 'scroll-timeline' property (in CSS)
+	or the {{AnimationTimeline}} parameters (in the Web Animations API).
+	The timeline range to which their [=active interval=] is attached
+	can also be further restricted to a particular timeline range
+	(see [[#named-range-animation-declaration]]).
+
+## Finite Timeline Calculations ## {#finite-attachment}
+
+	Unlike time-driven timelines,
+	[=scroll-driven timelines=] are finite,
+	thus [=scroll-driven animations=] are always attached
+	to a finite timeline range.
+	The animation’s delays ('animation-delay')
+	and iterations ('animation-iteration-count')
+	are set within the limits of this finite range.
+	If the specified duration is ''animation-duration/auto'',
+	then once any delays are subtracted,
+	the remaining range is divided by its [=iteration count=] ('animation-iteration-count')
+	to find the [=used value|used=] duration.
+
+	Note: If the animation has an infinite [=iteration count=],
+	each [=iteration duration=]--
+	and the resulting [=active duration=]--
+	will be zero.
+
+## Named Timeline Scoping ## {#timeline-scope}
 
 	A named [=scroll progress timeline=] or [=view progress timeline=]
 	is referenceable in 'animation-timeline' by: