use strict;
use warnings;

use XML::XPath;

my $xml = q|<?xml version="1.0" ?>
<xml><!-- A single line comment -->

<class_list>
	<student>
		<name>Robert</name>
        <!-- A comment deeply inside the file -->
		<grade>A+</grade>
	</student>
<!-- Here starts a multi line comment
	<student>
		<name>Lenard</name>
		<grade>A-</grade>
	</student>
-->
</class_list>
</xml>
|;

my $xp = XML::XPath->new(xml => $xml);

my $nodeset = $xp->find('/descendant-or-self::comment()');

foreach my $node ($nodeset->get_nodelist) {
    print "FOUND\n",
        $node->getValue,
        "\n";
}

##</code><code>##

FOUND
 A single line comment 
FOUND
 A comment deeply inside the file 
FOUND
 Here starts a multi line comment
	<student>
		<name>Lenard</name>
		<grade>A-</grade>
	</student>