Unable to extend iframe

[robdodson]

I was just messing around with type extensions and noticed that extending iframe throws the following error.

Uncaught HierarchyRequestError: Failed to execute 'createShadowRoot' on 'Element': Author-created shadow roots are disabled for this element.

ex:

<polymer-element name="x-iframe" extends="iframe">
  <template>
    <h1>Hello from x-iframe</h1>
  </template>
  <script>
    Polymer('x-iframe', {

    });
  </script>
</polymer-element>

<iframe is="x-iframe"></iframe>```

I didn't see any mention of this in the custom elements or shadow DOM specs. Is this behavior explained more elsewhere?

[dfreedm]

There are more than a few elements that you cannot add ShadowDOM to in Chrome: https://code.google.com/p/chromium/issues/detail?id=234020

I'm not sure if adding a shadowdom to iframe ever really makes sense, since it would make the contents from the frame hidden forever.