To use a namespace in an XPath expression, you have to register it first. The following works for me: 
#!/usr/bin/perl
use warnings;
use strict;

use XML::LibXML;

my $file_dati = '/path/to/file.xml';
my $parser    = 'XML::LibXML'->new();
my $doc       = $parser->parse_file($file_dati) || die('dead1');
my $xc        = 'XML::LibXML::XPathContext'->new($doc);

$xc->registerNs('mw', 'http://myweb.com');

my $nodetobefound = '//mw:comment[@timestamp="20130903225513"]';

print "To be found: $nodetobefound\n";

my $commento = $xc->findnodes($nodetobefound) || die('dead3');

print $commento->get_node(0)->toString();

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As Corion suggested, I changed the name of the element and added // for recursive search.

لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re: How to write an xpath query including attributes for an XML with namespace by choroba
in thread How to write an xpath query including attributes for an XML with namespace by topola1882

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