extension elements inside link elements?

[Eric Scheid]

> 4.2.9 The "atom:link" Element
> 
> The "atom:link" element is an empty element that defines a reference from an
> entry or feed to a Web resource.

did we want to prevent expressions like this:

    <link href=".." type=".." rel=".." title="..">
        <ext:foo .../>
    </link>

e.