[scroll-animations-1] Define before/after phases of a view timeline.

Author: fantasai

scroll-animations-1/rewrite.bs

@@ -220,15 +220,13 @@ spec: cssom-view-1; type: dfn;
 
 		:   <dfn>startTime</dfn>
 		::  Represents the [=scroll container=]’s startmost (reachable) scroll position
-			as its scroll offset in ''px''
-			when the timeline is [=timeline active phase|active=].
-			Null when it is [=timeline inactive phase|inactive=].
+			as its scroll offset in ''px''.
+			Null when the timeline is [=timeline inactive phase|inactive=].
 
 		:   <dfn>endTime</dfn>
 		::  Represents the [=scroll container=]’s endmost (reachable) scroll position
-			as its scroll offset in ''px''
-			when the timeline is [=timeline active phase|active=].
-			Null when it is [=timeline inactive phase|inactive=].
+			as its scroll offset in ''px''.
+			Null when the timeline is [=timeline inactive phase|inactive=].
 	</dl>
 
 	<dl class="constructors">
@@ -257,15 +255,14 @@ spec: cssom-view-1; type: dfn;
 	<dl>
 		:   {{AnimationTimeline/currentTime}} (inherited from {{AnimationTimeline}}
 		::  Represents the scroll progress of the [=scroll container=]
-			as its scroll offset in ''px''
-			when the timeline is [=timeline active phase|active=].
-			Null when it is [=timeline inactive phase|inactive=].
+			as its scroll offset in ''px''.
+			Null when the timeline is [=timeline inactive phase|inactive=].
 	</dl>
 
 	If the {{ScrollTimeline/source}} of a {{ScrollTimeline}}
 	is an element whose [=principal box=] does not exist
 	or is not a [=scroll container=],
-	then the {{AnimationTimeline/phase}} is the [=timeline inactive phase=].
+	then its {{AnimationTimeline/phase}} is the [=timeline inactive phase=].
 	It is otherwise in the [=timeline active phase|active=] phase.
 
 	Note: The {{ScrollTimeline/startTime}} and {{ScrollTimeline/endTime}} attributes
@@ -423,30 +420,30 @@ spec: cssom-view-1; type: dfn;
 		:   {{ScrollTimeline/startTime}} (inherited {{ScrollTimeline}}
 		::  Represents the starting (0% progress) scroll position
 			of the [=view progress timeline=]
-			as its [=scroll container=]’s scroll offset in ''px''
-			when the timeline is [=timeline active phase|active=].
-			Null when it is [=timeline inactive phase|inactive=].
+			as its [=scroll container=]’s scroll offset in ''px''.
+			Null when the timeline is [=timeline inactive phase|inactive=].
 
 		:   {{ScrollTimeline/endTime}} (inherited from {{ScrollTimeline}}
 		::  Represents the ending (100%) scroll position
 			of the [=view progress timeline=]
-			as its [=scroll container=]’s scroll offset in ''px''
-			when the timeline is [=timeline active phase|active=].
-			Null when it is [=timeline inactive phase|inactive=].
+			as its [=scroll container=]’s scroll offset in ''px''.
+			Null when the timeline is [=timeline inactive phase|inactive=].
 
 		:   {{AnimationTimeline/currentTime}} (inherited from {{AnimationTimeline}}
 		::  Represents the current progress
 			of the [=view progress timeline=]
-			as its [=scroll container=]’s scroll offset in ''px''
-			when the timeline is [=timeline active phase|active=].
-			Null when it is [=timeline inactive phase|inactive=].
+			as its [=scroll container=]’s scroll offset in ''px''.
+			Null when the timeline is [=timeline inactive phase|inactive=].
 	</dl>
 
 	If the {{ScrollTimeline/source}} or {{ViewTimeline/subject}} of a {{ViewTimeline}}
 	is an element whose [=principal box=] does not exist
 	or is not a [=scroll container=],
-	then the {{AnimationTimeline/phase}} is the [=timeline inactive phase=].
-	It is otherwise in the [=timeline active phase|active=] phase.
+	then its {{AnimationTimeline/phase}} is the [=timeline inactive phase=].
+	The timeline is otherwise
+	* in the [=timeline before phase|before=] phase when {{AnimationTimeline/currentTime}} < {{ScrollTimeline/startTime}}
+	* in the [=timeline active phase|active=] phase when {{ScrollTimeline/startTime}} &le; {{AnimationTimeline/currentTime}} &le; {{ScrollTimeline/endTime}}
+	* in the [=timeline after phase|after=] phase when {{ScrollTimeline/endTime}} < {{AnimationTimeline/currentTime}}
 
 	ISSUE: Figure out how to incorporate fit/inset abilities.