use strict;
use warnings;

use XML::LibXML;

my $xpc = XML::LibXML::XPathContext->new;
$xpc->registerNs('h', 'http://www.w3.org/1999/xhtml');

my $doc1 = XML::LibXML->new->parse_file('wiki.html');
my $doc2 = XML::LibXML->new->parse_file('timeline.html');

my ($node1) = $xpc->findnodes('//h:div[@id="metanav"]', $doc1);
my ($node2) = $xpc->findnodes('//h:div[@id="metanav"]', $doc2);

$node1->replaceNode($node2);

print $doc1->toString(0);