Specs: Some notes on combining simultaneous animations of the same property

sky/specs/animation.md

 Animation API
 =============
 
+(This is very incomplete, because it's all expected to be in the
+framework, not the platform.)
+
 ```javascript
 
 dictionary EasingFunctionSettings {
   Float duration; // required
   Callback? completionCallback = null;
 }
 
 abstract class EasingFunction {
   abstract constructor (EasingFunctionSettings settings);
   abstract Float getFactor(Float time);
     // calls completionCallback if time >= duration
     // then returns a number ostensibly in the range 0.0 to 1.0
     // (but it could in practice go outside this range, e.g. for
     // animation styles that overreach then come back)
 }
+```
 
 
-```
+If you want to have two animations simultaneously, e.g. two
+transforms, then you can add to the RenderNode's overrideStyles a
+StyleValue that combines other StyleValues, e.g. a
+"TransformStyleValueCombinerStyleValue", and then add to it the
+regular animated StyleValues, e.g. multiple
+"AnimatedTransformStyleValue" objects. A framework API could make
+setting all that up easy, given the right underlying StyleValue
+classes.