multiple files and signed nodes?

I have two issues I am interested in:

Can I specify an XPath that matches nodes across multiple files, perhaps 
specifying a pattern to match the filenames, or a directory to get them 
from?

Is there any way to specify with XPath that a node be signed with a 
specific public encryption key? perhaps, also, giving an XPath to the 
key, instead of giving it literally? If not, are there any plans for 
such a functionality and/or does anyone else see a need for such?