use strict;
use XML::Twig;
local $/;
XML::Twig->new(
  TwigHandlers => {
    '/root/msg' => sub { $_[1]->set_text('Twig is easy') }
  }
)->parse(<DATA>)->print;
__DATA__
<?xml version="1.0" encoding="iso-8859-1"?>
<root><msg>As a last resort XML::LibXML is also useful.</msg></root>