while  (my $token = $stream->get_token) {
  if (($token->[0] eq 'C' and 
       $token->[1] eq '<!-- InstanceBeginEditable name="article" -->')
      ..
       ($token->[0] eq 'C' and $token->[1] eq '<!-- InstanceEnd -->')){
    print $token->[1];
  }
}