use XML::LibXML::XPathContext qw( );

my $xpc = XML::LibXML::XPathContext->new();
$xpc->registerNs('nc', 'urn:ietf:params:xml:ns:netconf:base:1.0');
$xpc->registerNs('j', 'http://xml.juniper.net/junos/12.3R9/junos');

##</code><code>##

$xpc->findnodes(
   "/nc:rpc-reply/nc:vlan-information/nc:vlan", $doc)

$xpc->findnodes(
   "nc:vlan-name|nc:vlan-tag|.//nc:vlan-member-interface", $vlan)