final public static function register($type, $className, $includeFile = null)
    {
        $type = strtolower($type);
        if (!empty(self::$_types[$type])) {
            throw new HTML_QuickForm2_InvalidArgumentException(
                "Renderer type '$type' is already registered"
            );
        }
        self::$_types[$type] = array($className, $includeFile);
        if (empty(self::$_pluginClasses[$type])) {
            self::$_pluginClasses[$type] = array();
        }
    }