Enclosing fieldset's disabled attr does not disable polyfilled elements

[bennypowers]

Please consider https://codepen.io/bennyp/pen/KKemLEG?editors=1010

<form id="form">
  <fieldset id="set" disabled>
    <legend>This fieldset controls <code>x-checkbox</code></legend>
    <label for="xcheck">Check?</label>
    <x-checkbox id="xcheck" name="checkit"></x-checkbox>
  </fieldset>
</form>

In this case, using GNOME Web 43.0-66-g2cd7f8ec4+ (WebKitGTK 2.38.2), with the polyfill loaded, I observed that toggling disabled on the fieldset had no effect on x-checkbox.

Expected: :disabled or known-limitations equivalent should be applied to the FACE, mouse clicks should be prevented.

[calebdwilliams]

I'll try to work on this a bit unless you'd like to tackle it.

[bennypowers]

I can grab this one:

the MutationObserver will toggle the string value of aria-disabled on each associated child when fieldset parent's disabled changes