function addMilliseconds($milliseconds) {
        if (!is_int($milliseconds)) return false;
        if ($milliseconds == 0) return true;
        $millisecond = $this->millisecond + $milliseconds;
        $milliseconds = $millisecond % 1000;
        if ($milliseconds < 0) {
            $milliseconds += 1000;
        }
        $seconds = (int)(($millisecond - $milliseconds) / 1000);
        $millisecond = (int)$milliseconds;
        if ($this->addSeconds($seconds)) {
            $this->millisecond = (int)$milliseconds;
            return true;
        }
        else {
            return false;
        }
    }