WebIDL: How to define an extended/inherited interface?

[rjksmith]

I'm trying to define a new IDL interface that extends from an existing web interface.

interface MyInterface : WebInterface

The parent interface name does not resolve for HTML/DOM interfaces such as EventTarget or TextTrackCue, though this syntax does work if I substitute an interface defined within my own document.

I've not found an example of an inherited interface in the documentation and can't see how to resolve this issue. Please advise.

Example

In the following example, HTML TextTrackCue remains unresolved and causes an error.

    <section id='mycue-interface' data-dfn-for='MyCue'>
      <h2><dfn>MyCue</dfn> Interface</h2>
      <pre class='idl' title='MyCue Interface'>
        [Exposed=Window]
        interface MyCue : TextTrackCue {
          constructor(double startTime, unrestricted double endTime, any value);
          readonly attribute any value;
        };
      </pre>
      <dl>
        <dt>
          |cue| = new MyCue(startTime, endTime, value);
        </dt>
        <dd>
          Returns a new <a>MyCue</a> object.
        </dd>
        <dt>
          |cue|.<dfn>{{MyCue/value}}</dfn>
        </dt>
        <dd>
          Returns the value of a <a>MyCue</a> cue.
        </dd>
      </dl>
    </section>

Citing the parent interface as {{TextTrackCue}} doesn't fix the problem, and nor does adding pre class='idl no-link-warnings'. I'd welcome your guidance.

[rjksmith]

There has been a recent problem with Specref, but I believe that this is now resolved.