My swiss-army-knife for XML is XML::Twig, which I used for this:

#!/usr/bin/perl
use strict;
use warnings;

use XML::Twig;

my $t = XML::Twig->new();
$t->parsefile('x.xml');

my @errors = map {
    my %d = map {
        (my $tag = $_->tag()) =~ s/^m://;
        $tag => $_->text()
    } $_->children();
    \%d
} $t->get_xpath('//m:error');

use Data::Dumper; print Dumper \@errors;
[download]

The output is:

$VAR1 = [
          {
            'col' => '66',
            'message' => 'document type does not allow element "LINK" 
+here',
            'line' => '11'
          },
          {
            'col' => '41',
            'message' => 'document type does not allow element "LINK" 
+here',
            'line' => '14'
          },
          {
            'col' => '4',
            'message' => 'document type does not allow element "META" 
+here',
            'line' => '21'
          }
        ];
[download]

You can do the same for warnings and whatever else you have. With some practice with the xpath, you can ensure that you're getting just what you want.