{
my @constants = qw(scroll_x scroll_y flow_x flow_y);
sub which_constants {
  my $self = shift;
  return undef unless ref($self);
  my %hashtest;
  @hashtest{map { $_ - 1 } grep(/^\d+$/ && 0<=$_ && $_<@constants,@_)} = ();
  $self->{$constants[$_]} = exists $hashtest{$_} ? 1:0 for (0..$#constants);
  $self;
}
}