Bug 203364 – Pointer Events aren't properly captured when event target is nested

• Component: UI Events
• Status: NEW

I found that capturing a pointer id doesn't work properly if the source element of the pointer down event is nested inside the node bound to the event listener.
Here is a repro sandbox:

https://codesandbox.io/s/twilight-dew-76ii9

Using an iPhone with iOS 13.2 beta, I noticed that the green square stops registering events when you start dragging inside the inner node as soon as your finger moves out of the green square.

Reproduction steps:

1. Touch the green square inside the `drag me` node
2. Move your finger outside of the green square
3. You should notice that the log element stops updating as soon as your finger moves out of the green square.
4. If you do the same starting from outside the `drag me` inner node (but still inside green square), you should see the log updating even when your finger moves out of the green square.
5. If you do the same on the pink square, you should see the log updating even when your finger moves out of the pink square.

[Radar WebKit Bug Importer]

<rdar://problem/56597271>