Re: [pointerevents] Add OS image dragging to non-normative reasons for pointercancel

> pointercancel will be dispatched immediately before dragstart.

What about mouse event compatibility?  Is `mouseup` delivered reliably at the end of a drag sequence today?  If we `pointercancel` then presumably we won't send `pointerup` at the end (which could be confusing for existing code looking for `pointerdown` and `pointerup` pairs).  But would we still send a `mouseup`?

> If there was a pointer capture in place drag operation never starts (i.e. dragstart is never dispatched)

This conceptually makes sense to me but I wonder about the web compat implications.  Would this apply to the implict capture that occurs via touch also?  Edge (and Chrome on ChromeOS) supports HTML DnD for touch, so there's some potential compat implications there.

That doesn't mean we shouldn't change though, but it means we'll want to make some attempt to quantify the compat risk.  I need to read this thread in more detail and think through the implications.  Other than being confusing, how urgent/important is this?  A developer can always listen for `dragstart` to know they won't receive `move` events, and presumably developers who care about such things have long needed to do this for mouse events, right?

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Received on Wednesday, 14 June 2017 21:36:47 UTC