package dir_browse::dir_browse;
use Apache2::Module;
...
Apache2::Module::add(__PACKAGE__, [{name => 'START_DIR'}]);
...
sub handler : method {
  my ($self, $r) = @_;
...
  my $cfg = Apache2::Module::get_config(__PACKAGE__, $r->server, $r->per_dir_config) or throw Error;
  $self->{START_DIR} = $cfg->{ST_DIR};
...
}

sub START_DIR {
  my ($cfg, $parms, $arg1) = @_;
  $cfg->{ST_DIR} = $arg1;
}