[scroll-animations-2] Define specified/computed/used keyframe sort orders.

Author: fantasai

css-animations-2/Overview.bs

@@ -302,10 +302,6 @@ its associated [=keyframes=] are generated as follows:
         In this case no animation is generated,
         and any existing animation matching |name| is canceled.
 
-    1.  Perform a stable sort on all [=keyframe blocks=] in the ''@keyframes'' rule
-        by their specified <<keyframe-selector>>
-        (treating ''@keyframe/from'' as ''0%'' and ''@keyframe/to'' as ''100%'').
-
     1.  Group together all [=keyframe blocks=]
         that share the same [=specified value|specified=] <<keyframe-selector>>
         (treating ''@keyframe/from'' as ''0%'' and ''@keyframe/to'' as ''100%''),
@@ -356,6 +352,26 @@ its associated [=keyframes=] are generated as follows:
         that is not already assigned to a [=keyframe=] in |keyframes|
         that has a matching |keyframe offset|.
 
+1.  <strong>Sort Frames:</strong>
+
+    *   The <dfn lt="specified keyframe order">specified order</dfn> of |keyframes|
+        is the order resulting from the steps above,
+        i.e. document order with duplicate keyframes collapsed
+        to the earliest position.
+
+    *   The <dfn lt="computed keyframe order">computed order</dfn> of |keyframes|--
+        which is the order returned by {{KeyframeEffect/getKeyframes()}}--
+        is found by performing a stable sort on |keyframes|
+        by each keyframe’s |keyframe offset|.
+
+    *   The <dfn lt="used keyframe order">used order</dfn> of |keyframes|--
+        which is the order used to interpolate and compute the actual animation frames--
+        is found by attaching the |keyframes|
+        onto the animation effect’s timeline
+        assuming an [=iteration count=] of 1
+        and ordering them from earliest to latest,
+        breaking ties by using the [=computed keyframe order=].
+
 <h2 id="animation-definition">
 Declaring Animations</h2>