I dont know whether i understood the question correctly. As you mentioned that each line in the file is single XML statement, I used XML::Twig to check the element and attributes by processing the file line by line.

This below code will print the line number at which you find the discrepancy. You can tweak this code to accommodate the changes you need.

#!/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>
[download]