package MyDoc;
@ISA = qw(XML::LibXML::Document);

my %instance_hashes;

sub new {
  my $class = shift;
  my $self = $class->SUPER::new('1.0', 'UTF8');

  my @listeners = ();

  # initialize private hash data
  $instance_hashes{$self} = {};

  $self->listener(\@listeners);
  bless $self, $class;
}

# accessor / mutator
sub listener {
  my $self = shift;

  if (@_) {
    $instance_hashes{$self}{Listeners} = shift;
  }

  return $instance_hashes{$self}{Listeners};
}