public function callback_before_delete($callback = null, $override_all = 0) { if (!$override_all) { $this->callback_before_delete_ext[] = $callback; if ($this->callback_before_delete == null) { $this->callback_before_delete = array($this, 'extended_callback_before_delete'); } } else { parent::callback_before_delete($callback); } return $this; }