protected function _expandPlugin($file)
    {
        preg_match(self::PLUGIN_PATTERN, $file, $matches);
        if (empty($matches[1]) || empty($matches[2])) {
            throw new RuntimeException('Missing required parameters');
        }
        if (!CorePlugin::isLoaded($matches[1])) {
            throw new RuntimeException($matches[1] . ' is not a loaded plugin.');
        }
        $path = CorePlugin::path($matches[1]);

        return $path . 'webroot' . DS . $matches[2];
    }