#!/usr/bin/perl
use strict;
use XML::Twig;

my %elem_att = qw(cat meow dog bark);
my $reg = join '|', keys %elem_att;

while (<DATA>) {
	next unless (m/<(?:$reg)/);
	my $line = $_;
	my $line_num = $.;
	my $elt = parse XML::Twig::Elt($line);
	my $element = $elt->name;
	my $att = $elem_att{$element};
	unless ($elt->att_exists($att)) {
		print "Attribute $att is not found at line number $line_num\n";
		next;
	}
}


__DATA__
<root>
<a/>
<b/>
<cat tail='text' meow='text'/>
<cat tail='text'/>
<cat tail='text'/>
<dog tail='text' bark='text'/>
<dog tail='text'/>
</root>