Currently, the Sequential and Parallel transitions accept any Animation as their child. The problem is that Animations doesn't have any common interface that could be used to observe what the animation will do.

This is problem in e.g. RT-25776, where SequentialTransition doesn't know what properties need to be set to the starting value at the beginning of the Transition. Having some common interface that describes Animations (like KeyFrames ? ) would allow this.