use strict;
use warnings;
use XML::Twig::XPath;

$/ = undef;
my $data = <DATA>;
 my $twig=XML::Twig::XPath->new(pretty_print => 'nice',
                                keep_encoding=>1,
                                twig_handlers   => {
                                                     'add' => \&_checkAdd,
                                                   }
                               );
$twig->parse($data); # build ito

 my $out =  $twig->sprint;
print $out;

sub _checkAdd
{
  my( $t, $addAttr)= @_;
        my $elt;
        $addAttr->set_tag('check');
        $elt= parse XML::Twig::Elt( qq(<p>test</p>) );
        $elt->paste('last_child',$addAttr);
}

__DATA__
<?xml version="1.0" encoding="ISO-8859-1"?>
<doc><url><irl>with &#xDC; here</irl></url><add></add></doc>