[selectors-4] Disallow pseudo-elements inside :has()

[mozilla-apprentice]

A resolution was made for csswg-drafts/#7463.

[selectors-4] Disallow pseudo-elements inside :has()

• RESOLVED: Disallow all current pseudo-elements inside of :has(), allow future pseudo-elements to define that they are valid if useful/possible.

Discussion.

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[dholbert]

We haven't implemented :has yet (beyond some basic parsing); https://bugzilla.mozilla.org/show_bug.cgi?id=418039 is the tracking bug for the feature. So, we probably don't need a dedicated bug for this spec change.

I'll add a note on bug 418039 mentioning this working-group resolution, in case it hasn't made it into the spec yet when we start implementing.