Re: [csswg-drafts] [css-contain-2] If element is in the top layer, are its contents necessarily relevant to the user (#8514)

@tabatkins The contents are not directly "in the top layer" or these would apply:

https://fullscreen.spec.whatwg.org/#new-stacking-layer

> Each element and [::backdrop](https://fullscreen.spec.whatwg.org/#css-pe-backdrop) pseudo-element in a [top layer](https://fullscreen.spec.whatwg.org/#top-layer) has the following characteristics: [lots of things that don't happen]

https://fullscreen.spec.whatwg.org/#::backdrop-pseudo-element
> Each element in a [top layer](https://fullscreen.spec.whatwg.org/#top-layer) has a ::backdrop pseudo-element.

Basically, the cases are:
 1. Element with `content-visibility: auto` has contents in the top layer. These contents would be reparented and escape containment, so it can be observable whether they are skipped or not. So we don't want to skip contents.
 2. Element with `content-visibility: auto` is itself in the top layer. Such thing has a `::backdrop` content in the top layer, so this actually fits into the previous case.
 3. Element with `content-visibility: auto` has ancestors in the top layer. I see no need to prevent skipping its contents.

The spec covers cases 1 and 2. The test is for case 3.

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Received on Wednesday, 1 March 2023 23:36:22 UTC