my $t= XML::Twig->new( elt_class => 'my_elt_class',
                       p => sub { $_->cut         # an XML::Twig::Elt method
                                    ->my_process; # a my_elt_class method
                                }
                     );

package my_elt_class;
BEGIN { @my_elt_class::ISA=('XML::Twig::Elt'); } # to inherit from XML::Twig::Elt

sub my_process
  { my $elt= shift;
    # stuff here
  }