[css-forms-1] Should new pseudo-elements be restricted to base appearance mode?

[lukewarlow]

There's been recent discussions surrounding ::file-selector-button and the fact it's exposed in appearance: auto and how that's not necessarily desirable.

Should we update CSS forms to restrict all new pseudo-elements to just elements in base appearance mode?

We'd probably have to explicitly allow ::file-selector-button and ::placeholder to break that rule as they're pre-existing.

The spec already limits ::checkmark and ::picker-icon to just base appearance mode.

cc @nt1m @annevk

[lukewarlow]

We'd have to update https://drafts.csswg.org/css-forms-1#vendor-pseudo-element-compatibility and mentions of appearance:textfield restricting certain pseudos (given they'd only be in base appearance anyway)

[nt1m]

appearance: none should get new pseudo-elements ideally as well, so I'm inclined to disagree here.

[kbabbitt]

I haven't gotten around to drafting the spec text for it yet, but we did resolve in #11845 (comment) that the password reveal pseudo-element would be available outside of base appearance.

[lukewarlow]

appearance: none should get new pseudo-elements ideally as well, so I'm inclined to disagree here.

Ah I was mostly thinking of the appearance: auto case. Should we perhaps exclude these from matching in appearance: auto?

Though I agree the password reveal one is a case where that doesn't apply.

One downside to applying the pseudo elements in auto mode is we either have to prescribe limitations to them when in auto mode (such as not being an element backed pseudo element if that's even possible to do conditionally) or we have to specify that browsers implement auto mode in a specific way?