Amphtml: Can't bind aria attributes

[jcayzac]

What's the issue?

Unless I'm doing things wrong, ARIA attributes cannot be bound to a state. This hinders implementing proper accessibility.

How do we reproduce the issue?

<amp-state>
  <script type='application/json'>
    {
      "navOpen": false
    }
  </script>
</amp-state>
<button [aria-expanded]='(navOpen ? "true" : "false")' on='tap:AMP.setState({navOpen: !navOpen})'>Menu</button>

The state gets updated, and so do other attributes I've bound in my page (mostly just [class]).

What browsers are affected?

Chrome 62.0.3202.29 for macOS.

Which AMP version is affected?

AMP version 1506043780363

[aghassemi]

/to @choumx Hopefully low-effort, will high-impact for a11y

[choumx]

Thanks for reporting this. The fix has been merged, but it'll take a couple weeks for validator changes to rollout.