Does not polyfill invokers in declarative shadow DOM

[sntran]

Steps to reproduce

Add an element with declarative shadow DOM with an invoker in it:

<header>
  <template shadowrootmode="open">
    <button command="toggle-popover" commandfor="menu">Menu</button>
    
    <menu id="menu" popover="">
      Menu
    </menu>
  </template>
<header>

Include the polyfill script.

View the page in Safari 18.x.

Here is a codepen for the above: https://codepen.io/sntran/full/LENaVoN

Expected result

• Clicking Menu button should popover the menu element.

Actual result

• Nothing happen.

Observations

The polyfill does handle shadow DOM, but it seems that the browser does not call either attachShadow nor attachInternals when declarative shadow DOM is used.

[keithamus]

Unfortunately there's no way to efficiently access such shadowroots, as far as I know.

PRs welcome if someone discovers such a technique.

[sntran]

Would it be feasible to let apply take a root element and default to document? End user can call apply(elementOfInterest.shadowRoot) if needed.

[keithamus]

Yes certainly.