use XML::Twig;

$str ='<chap>
  <ch>
    <sec>
      <p>
        <anchor>THE ILIAD</anchor>
        <author>HOMER</author>
      </p>
    </sec>
    <sec>
      <p>
      <anchor>BOOK I</anchor>
        <para>
          Sing, O goddess, the anger of Achilles son of Peleus, that
          brought countless ills upon the Achaeans.
        </para>
       </p>
    </sec>
  </ch>
</chap>
';

$epath = '<chap/<ch/<sec//<anchor';
$relt = 'anchors';

$epath =~ s/<//g;
my $twig = XML::Twig->new(
		twig_handlers => { $epath => sub { normal (@_, $relt)},
		 pretty_print => 'indented'
												);
$twig->parse("$str");
#$twig->print;

sub normal
{
	my ($twig, $elt, $relt) = @_;
	$elt->set_gi( "$relt"	);
	#$elt->print;
}

##</code><code>##

Error:
unrecognized expression in handler: 'chap/ch/sec//anchor' at D:\ver\conversion.pl line 132