public function format($format = self::FORMAT_COMPLETE)
    {
        if (!$this->hasValidFormat()) {
            return false;
        }
        switch ($format) {
            case static::FORMAT_COMPLETE:
                return $this->join(
                    number_format($this->number, 0, null, "."),
                    $this->vn
                );
                break;

            case static::FORMAT_WITH_DASH:
                return $this->join($this->number, $this->vn);
                break;
        }
        return $this->number . $this->vn;
    }