Should event timing implications be explicit?

[RByers]

Even though requiresCancelable=false allows scrolling to proceed without blocking on JS, that should not mean that developers will see the touch events at a location/target different from what the user actually touched. Hit testing behavior / observable event ordering must remain the same. This should fall out naturally in chromium due to the design of threaded scrolling and (since hit-testing isn't specified) is probably out of scope for this document. But maybe a note is deserved? It should be easy to create a test page that demonstrates this.

[RByers]

Keeping this open on me for now to build a test page for this once @dtapuska has a working implementation in chromium. I doubt we'll want to add anything to the spec, but it's worth exploring further.