protected function _validateLoaderType($type)
    {
        $type = strtolower($type);
        if (!in_array($type, $this->_loaderTypes)) {
            $types = implode(', ', $this->_loaderTypes);

            throw new Zend_Http_UserAgent_Exception(sprintf(
                'Expected one of "%s" for plugin loader type; received "%s"',
                $types,
                (string) $type
            ));
        }
        return $type;
    }