use XML::LibXML;
use XML::LibXML::XPathContext;
                                                                                
my $xml = q{<?xml version="1.0" encoding="iso-8859-1"?>
<Tag1 xmlns="urn:wow">
  <Foo>content</Foo>
</Tag1>
};
                                                                                                                                                               
                                                                                
my $doc = XML::LibXML->new->parse_string($xml);
my $xc = XML::LibXML::XPathContext->new($doc);
$xc->registerNs('foo', 'urn:wow');
                                                                                
my ($foo) = $xc->findnodes('//foo:Tag1/foo:Foo');
                                                                                
print "Foo in xml: ".$foo->textContent()."\n";