[web-animations] AnimationPlayer.source

[Jonathan Watt]

Can the AnimationPlayer.source property *please* be renamed? The word "source" 
doesn't seem to make any sense, and would seem to imply it points to the element 
or something. It pointing to the Animation object was completely 
counterintuitive to me, since I'd think of the relationship being reversed. I.e. 
the AnimationPlayer controls the Animation, and in that way its actions "target" 
the Animation, which is the inverse direction of a source<->target relationship.

I'm not sure "target" is a good name though, since to the uninitiated on anyone 
not frequently dealing with animations scanning through code that again would 
likely look like it refers to the element. I'd suggest calling it "animation".