#!/usr/bin/perl
use XML::LibXML;
my $parser = XML::LibXML->new();
$parser->validation(1);
my $doc = $parser->parse_string(<<'EOT');
<?xml version="1.0"?>
<!DOCTYPE airg SYSTEM "thedtd.dtd">
<xml/>
EOT

print $doc->is_valid eq 1?"is cool\n":"error\n";