When exactly does the determination of default action happen?

Hi,
The PE spec says "When a user touches an element, the effect of that touch
is determined by the value of the touch-action property and the default
touch behaviors on the element and its ancestors.".  But _when_ exactly is
meant by "when a user touches an element"?  Does it mean as soon as the
user first touches before anything has processed that touch?  Or might it,
for example, mean "just before the pointerdown event is dispatched"?

Here's a concrete class of issues causing us trouble in Chrome, that I'm
wondering if pointer events should fix: sites that set overflow: scroll
only when the mouse cursor is over the element (for example, the chat
roster in gmail).  If touch-action is truly applied as soon as the user
starts touching, then we'll see overflow: none and no touch scrolling will
be possible (as with touch events).  If instead touch-action is checked
just before pointerdown is dispatched, then we will (according to the mouse
event compat rules) have already dispatched the mousemove event which will
trigger overflow: scroll, and you should be able to scroll it fine.

I'm travelling this week so don't have access to a Win8 touch device to
test IE10's behavior - sorry.

Thanks,
   Rick