public static function register($prepend = false)
    {
        if (self::isRegistered()) {
            return false;
        }
        if (!is_bool($prepend)) {
            $prepend = (bool) $prepend;
        }

        if (version_compare(PHP_VERSION, '5.3.0', '<')) {
            self::$_isRegistered = spl_autoload_register(self::$_callback);
        } else {
            self::$_isRegistered = spl_autoload_register(
                self::$_callback,
                true,
                $prepend
            );
        }
        return self::$_isRegistered;
    }