code: public function regenerate($delete_old = false) {
          if ($this->is_active()) {
              // Regenerate the session id
              @session_regenerate_id($delete_old);
          } else {
              $this->open();
          }
  
          return session_id();
      }
docs: Generates a new session id and returns it.
  
  $id = $session->regenerate();
  
  @return  string