public function call_hook($sWhich = '')
    {
        if (!isset($this->aCustomHooks[$sWhich])) {
            return parent::call_hook($sWhich);
        }

        if (isset($this->aCustomHooks[$sWhich][0]) && is_array($this->aCustomHooks[$sWhich][0])) {
            foreach ($this->aCustomHooks[$sWhich] as $aCustomHook) {
                $this->runCustomHook($aCustomHook);
            }
            return true;
        } else {
            $this->runCustomHook($this->aCustomHooks[$sWhich]);
            return true;
        }

        return parent::call_hook($sWhich);
    }