[css-animaiton-worklet] Update group effect wording

Author: majido

css-animationworklet/Overview.bs

@@ -930,11 +930,28 @@ To <dfn>set animator instance of worklet animation</dfn> given
 
 </div>
 
+Effect Stack and Composite Order {#effect-stack-composite-order}
+----------------------------------------------------------------
+
+As with other animations, <a>worklet animations</a> participate in the <a>effect stack</a>.  A
+worklet animation does not have a specific <a>animation class</a> which means it has the same
+composite order as other Javascript created web animations.
 
 
 
+
+
+Additional Related Concepts {#related-concepts}
+===============================================
+
+
 Worklet Group Effect {#worklet-group-effect}
-===========================================
+--------------------------------------------
+<em>This section is not normative.</em>
+
+
+<a>Group effect</a> is a type of <a>animation effect</a> that enbales multiple child animation
+effects to be animated together as a group.
 
 {{WorkletGroupEffect}} is a type of <a>group effect</a> that allows its <a>child effect's</a>
 <a>local times</a> to be mutated individually.
@@ -951,11 +968,16 @@ interface WorkletGroupEffect {
 };
 </xmp>
 
+
 Issue(w3c/csswg-drafts#2071): The above interface exposes a conservative subset of GroupEffect
 proposed as part of web-animation-2. We should instead move this into a delta spec against the
 web-animation.
 
 
+Note: Group Effect is currently an experimental feature and not well specified in web animations. So
+the concept of {{WorkletGroupEffect}} may change dramatically as <a>Group Effect</a> get specified.
+See https://github.com/yi-gu/group_effect/blob/master/README.md for more details.
+
 
 ScrollTimeline {#scroll-timeline}
 ---------------------------------
@@ -974,14 +996,6 @@ right abstractions and mechanisms to do this.
 
 
 
-Effect Stack and Composite Order {#effect-stack-composite-order}
-----------------------------------------------------------------
-
-As with other animations, <a>worklet animations</a> participate in the <a>effect stack</a>.  A
-worklet animation does not have a specific <a>animation class</a> which means it has the same
-composite order as other Javascript created web animations.
-
-
 Security Considerations {#security-considerations}
 ==================================================