Basic question: what should the base URI be for a node that's part of a
shadow tree that comes from some URI that's not the document URI?
Making it be the base URI of the resulting ownerDocument is nice and
simple and involves no spec changes and means that relative URIs to
things like stylesheets or images are totally unusable in the shadow DOM
if it's meant to be included in documents that have different base
URIs... and so are absolute ones, really. This is the behavior
Mozilla's XBL has right now, but it's pretty busted, in my opinion.
So what do we actually want here?
-Boris
