code: func (c *cidrs) Set(value string) error {
  	// On first Set(), clear the original defaults
  	if !c.isSet {
  		c.isSet = true
  		c.ipn = make(utilnet.IPNetSet)
  	} else {
  		return fmt.Errorf("GCE LB CIDRs have already been set")
  	}
  
  	for _, cidr := range strings.Split(value, ",") {
  		_, ipnet, err := net.ParseCIDR(cidr)
  		if err != nil {
  			return err
  		}
  
  		c.ipn.Insert(ipnet)
  	}
  	return nil
  }
docs: // Set supports a value of CSV or the flag repeated multiple times