[webappsec] Handling custom elements in CSP

I recently noticed the following proposal for custom elements in HTML:

https://www.w3.org/Bugs/Public/show_bug.cgi?id=18669#c48

We should think about how to handle these in CSP.  To my knowledge (please correct me) this is the first time there has been a notion of extension/inheritance in HTML tags.  This may be the easiest way to deal with these elements - policies apply to the described elements and any custom elements that descend from them.

For elements that are declared de-novo but have "active" or script-equivalent semantics, the case is a little more tricky.

Ideas?

-Brad Hill