my $parser = XML::LibXML->new();
my $doc = $parser->parse_string($xml_sitemap);
print $doc->getDocumentElement->getNamespaces->getValue, "\n";
my $xpc = XML::LibXML::XPathContext->new();
$xpc->registerNs('x', $doc->getDocumentElement->getNamespaces->getValue);

foreach my $u ($xpc->findnodes('//x:loc/child::text()',$doc)) {
        my $url = $u->toString;
        .......
}