Re: [csswg-drafts] [cssom-view] elementFromPoint, elementsFromPoint, and caretPositionFromPoint should not return an element inside a shadow tree (#556)

I recently found myself needing to write an engine-independent `DocumentOrShadowRoot.elementsFromPoint()` method. See https://github.com/semolina-solutions/layer-aware-pointer-events/blob/211c8c1c983f641e45e374f0d56040670ccd869e/lib/index.ts#L223.

While I'm naive to the internal implementation details in each engine, I found that Gecko's `elementsFromPoint()` output differs in two ways at the time of writing:

1. Gecko will return elements only within that DOM, rather from the `html` element.
2. When an element with `pointer-events: none` styling is queried from its Shadow DOM in Gecko, it will always be included in the resulting list, despite itself not being a potential event target.

Whether or not elements in open shadow DOMs should be included in higher-level `elementsFromPoint()` calls is somewhat arbitrary IMO, although including them would avoid needing to repeatedly and expensively query from each shadow root to build up the full picture. It'd be advantageous to have a `deep = true` setting to pierce through all open shadow DOMs below.

It'd be nice however to address difference no. 2, i.e. the inconsistency of a shadow root host element being included in the `ShadowRoot.elementsFromPoint()` when it's styled to ignore pointer events. It's good that it's included queries of higher-level DOMs, because it indicates that "there's _something_ in this shadow DOM that is reactive to pointer events".

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Received on Wednesday, 21 August 2024 10:21:14 UTC