XML::XPath doesn't really have have a mechanism for getting the whole document as a string so you have to do something like:

my $document = ($foo->findnodes('/'))[0]->toString();
[download]

and then you can print that to a file in the usual way.

Update: derby, is of course correct. The (unfortunately undocumented) getNodesAsXML() does  return $self->findnodes_as_string('/'); if no path is provided, however findnodes_as_string() comes with the caveat: "The result is not guaranteed to be valid XML though.", which may or may not also be true of my version.

/J\