Add a flag for elements which cannot have shadow trees about html HOT 8 CLOSED

"Private shadow tree content"? Bit long.

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What do you think of flag vs. kind of content? I kind of like the latter now that I look at it.

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I wonder why element groups such as "form-associated elements" or "Submittable elements" are not part of that. It seems "kind of content" is perhaps mostly about document conformance?

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I think you are right. Looking at https://html.spec.whatwg.org/#content-models in more detail it's largely about that.

Hmm. Do you have any idea besides adding a sentence like "xxx elements have private shadow tree content" to all the relevant elements? A centralized list seems nicer, like the ones you mention, but I am not sure what section it would belong in.

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Probably either a new section nested in "Common DOM interfaces" (2.7) or "Elements" (3.2).

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FWIW, the flag (virtual function actually) is called areAuthorShadowsAllowed() in Blink. So I guess the "allow shadow root flag" or similar?

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Media elements (<audio> and <video>) should also be excluded.

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Closing this per the PR. For now the relevant method in Shadow DOM will simply have a safelist.

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