default namespace in constructed element

Consider, we have the document a.xml: <?xml version="1.0"?><a/>

and the following expression:

<b xmlns="www.xyz.com">{doc("a.xml")//a}</b>

I'm puzzled about the result of the expression: i.e should the default
namespace declaration change the URI of  the insereted element from document
"a.xml" or not?

Regards, Leonid Novak
www.modis.ispras.ru