[whatwg] Fallback behavior

[Martin Atkins]

Maciej Stachowiak wrote:
> 
> As far as I can tell, the current spec does not adequately define how 
> fallback behavior works. Specifically, what should be done with fallback 
> content when not falling back?
> 
> Presumably it should be parsed into the DOM, but should not render - 
> that's the de facto behavior.
[snip]

Also,

<object id="movie" data="movie.ogg">
    <object id="movie" data="movie.mov">
       <object id="movie" data="movie.asf">
          <p>Blah blah movie alternative text...</p>
       </object>
    </object>
</object>

If these things remain in the DOM, authors will presumably need to give 
them all distinct "id" values.

Now if I want to access these things from script, such as to provide an 
alternative player UI, I need to somehow determine which one is actually 
being used in order to target it. If they're all in the DOM, I can't 
just rely on getElementById returning null for the unused cases.

What's the solution in this case?