my $x = new Tinia_CanExtender() ;
  my $y = new Tinia_CanPwm($x) ;

package Tinia_CanPwm ;

@ISA = qw(Tinia_CanExtender);

sub new {
  my $class = shift ;
  my $this = bless({} , $class) ;
  
  my ( $parent ) = @_ ;
  
  $this->{PARENT} = $parent ;
  
  return $this ;
}

package Tinia_CanExtender ;

sub new {
  my $class = shift ;
  my $this = bless({} , $class) ;
  return $this ;
}

sub set {
  my $self = shift ;
  my ($state,$set_by) = @_;
  ...
}