sub handler($) {
  my $r = shift;   # Apache2::RequestRec
 
  my $templ = select_template($r);
  my $vars  = fetch_data_for_output($r);
  my $tt    = Template->new(...);
  
  $r->content_type('text/html');
  $tt->process($templ,$vars,$r);
  
  return Apache2::Const::OK;
}