I just have a look at the XPathNSResolver interface.
In the Selectors spec, the selector "elm" is equivalent to "*|elm" in
the case of a missing default namespace, but "ns|elm" where "ns" is
the default namespace if a default namespace is declared.
The XPathNSResolver interface specifically states that it must never
be called with a null or empty argument. I imagine the Selectors API
would want to be able to send a null argument as a way to ask for the
default namespace, or be given some equivalent functionality.
David "liorean" Andersson