# cgi.pl

use strict;
use warnings;

@One::ISA = @Two::ISA = 'Zero';

{
  package Zero;
  use base 'CGI::' . shift;

  sub dispatch { shift->param ? 'Two' : 'One'; }

  sub render {
    print my $self = shift, "\n";
    print "$_: " . $self->param( $_ ) . "\n" for $self->param;
  }
}

@MY_Zero::ISA = 'Zero';

shift->activate;

__END__

##</code><code>##

# CGI/Classic.pm

use strict;
use warnings;

{
  package CGI::Classic;

  use CGI;

  my $CGI;

  sub activate {
    $CGI = CGI->new;
    shift->dispatch->render;
  }

  sub param { shift; $CGI->param( @_ ) };

  sub dispatch { die 'subclass responsibility' }
  sub render   { die 'subclass responsibility' }
}

1;
__END__

##</code><code>##

shift;   # discard script's second argument
Zero->new( 'parent*' => 'Zero' )->activate;