[cssom-view] which elements' pointer-events to look at when performing scroll gestures

[heycam]

When using the mouse wheel or trackpad to scroll, and there are ancestors that can also start scrolling when we reach the end of the element on top, which elements' pointer-events values do we look at to determine which elements are allowed to scroll?

[flackr]

My understanding is that scroll effectively bubbles up the DOM tree in the same way as a bubbling event. I.e. we should determine the element that was hit (considering pointer-events) and then the element which is scrolled is the nearest ancestor which can scroll in the given direction respecting the touch-action restrictions if using touch or stylus and overscroll-behavior when bubbling (or chaining) past a scrolling box.