:read-only and :read-write selectors: Consistency and cross-UA behavior

[js-choi]

This is a cross-post of w3c/csswg-drafts#127 by @cvrebert, because its issues are more relevant to HTML than to CSS.

Copying this over from http://lists.w3.org/Archives/Public/www-style/2016Apr/0294.html
(Disclaimer: My opinions are my own, not my employer's.)

:read-only is currently spec'd as (basically) :not(:read-write), and :read-write is currently spec'd as matching:

• <input> elements to which the readonly attribute applies, and that are mutable (i.e. that do not have the readonly attribute specified and that are not disabled)
• <textarea> elements that do not have a readonly attribute, and that are not disabled
• elements that are editing hosts or editable and are neither <input> elements nor <textarea> elements (i.e. contentEditable / designMode)

(A) This leads to an anomaly: Some inputs that the user can interact with to alter their "value" (which most folks would thus casually deem "writable") match :read-only instead of :read-write.
Namely, <input>s of type range, color, checkbox, radio, and file are :read-only since the readonly attribute doesn't apply to them.
(One can argue that this is a bug in HTML and that HTML should just allow the readonly attribute on these input types.)

(B) There's a question of whether the buttonish <input>s (types: image, submit, reset, button) should be :read-only or :read-write. Arguably, they should be :read-only since the user cannot normally directly modify their values. They are interactive insofar as they're clickable, but they aren't editable. However, Chrome and Edge currently have them matching :read-write, which doesn't conform with the current spec.

(C) There's a question of whether <input type="hidden"> should match :read-only or :read-write or neither. Per spec, it currently matches :read-only. But in Chrome and Edge, it currently matches :read-write.

(D) I think there's some question as to how useful the contentEditable case is, particularly when it's lumped together with the form input cases.

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Current state of affairs (FWICT):

• WebKit matches the current spec and doesn't want to change their implementation until the spec itself is changed.
• Blink and Edge both suffer from 2 bugs relative to the current spec:
  • :read-only doesn't match <input>s to which the readonly attribute does not apply
    • https://bugs.chromium.org/p/chromium/issues/detail?id=604154
    • https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/7229941/
      • As stated in a comment and on the www-style thread, the Edge folks (understandably) don't think the spec's current behavior here makes sense.
  • :read-write shouldn't match <input disabled> or <textarea disabled>
    • https://bugs.chromium.org/p/chromium/issues/detail?id=604117
    • https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/7226201/
    • (Gecko's prefixed implementation also suffers from this bug)
      Gecko currently only has a prefixed implementation. Relative to the current spec, it has the one aforementioned bug.
  • Feature request / unprefixing bug: https://bugzilla.mozilla.org/show_bug.cgi?id=312971

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And in light of the lack of compatibility and questions about the utility of these pseudos as-then-specd, it looks like Hixie asked the spec editors ~3 years ago in https://www.w3.org/Bugs/Public/show_bug.cgi?id=17812#c24 whether :read-only & :read-write could be removed from the spec altogether, but he never got a reply.

[js-choi]

@cvrebert: Done. I think I fixed everything.

[annevk]

In that bug I see @tabatkins arguing for a slightly different definition as well, whereby, e.g., <select> is also matched. Any change at this point though needs implementer buy-in given how close everyone is relative to the standard.

cc @whatwg/css

[emilio]

So Safari is shipping the spec afaict. I'm fixing Gecko to follow the spec and unprefix the pseudo-classes, and I reopened https://bugs.chromium.org/p/chromium/issues/detail?id=255351.

So this can probably be closed for now if there's nobody actively working on changing the spec further?

[rniwa]

Can we close this issue given Gecko is aligning their behavior to WebKit's, and WebKit has no intention of changing it. Or is Google / Blink strongly objecting to the current behavior?