Re: [csswg-drafts] [css-shadow-parts-1] vendor prefixed pseudo elements support (#4530)

Undefined, basically by definition - they're vendor-prefixed because they're not standardized, so the CSSWG doesn't define how they act. This should be raised against the browser vendor to decide.

I can see arguments either way, fwiw:

* On the pro side, this seems self-evidently useful.
* On the con side, this exposes internal details of how the part is implemented. This is precisely why sub-parts have to be explicitly forwarded by the component for them to be visible in the outer page. (::before/etc are present on *all* elements, so it doesn't expose anything, beyond just whether or not the component is also using the pseudo.)
* Back on the pro side, components *can* forward sub-parts into their own exposed parts, surfacing useful bits when needed. But there's no syntax for forwarding built-in pseudos, so forbidding it *by default* would also forbid it *at all times*.

Overall, I *suspect* the morally correct answer is to lean towards not exposing them, but I suspect the practically correct answer is to expose them.

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Received on Wednesday, 14 April 2021 16:15:47 UTC