code: func validatePortRange(portRange string) bool {
  	strs := strings.Split(portRange, "-")
  	if len(strs) != 2 {
  		klog.Errorf("port range should be in the format of `a-b`")
  		return false
  	}
  	for i := range strs {
  		num, err := strconv.Atoi(strs[i])
  		if err != nil {
  			klog.Errorf("Failed to parse %s, error: %v", strs[i], err)
  			return false
  		}
  		if num < 0 {
  			klog.Errorf("port number %d should be >=0", num)
  			return false
  		}
  	}
  	return true
  }
docs: // checks if port range is valid. The begin port number is not necessarily less than
  // end port number - ipset util can accept it.  It means both 1-100 and 100-1 are valid.