Hi All, AnimationTiming interface definition is the following (https://w3c.github.io/web-animations/#the-animationtiming-interface):
The AnimationTiming interface is a mutable subclass of AnimationTimingReadonly returned for the timing attribute of a mutable animation node such as Animation. But Animation interface doesn't contain any mutable timing properties. It has only readonly attribute AnimationTimingReadonly timing; inherited from AnimationNodeReadonly. Mutable override should be added -- Thank you, Sergey G. Grekhov
