public static function on($class, $name, $handler, $data = null, $append = true)
    {
        $class = ltrim($class, '\\');
        if ($append || empty(self::$_events[$name][$class])) {
            self::$_events[$name][$class][] = [$handler, $data];
        } else {
            array_unshift(self::$_events[$name][$class], [$handler, $data]);
        }
    }