code: func (c *Cluster) AddVIPSubnet(subnet *net.IPNet) error {
  	key := subnet.String()
  	if _, ok := c.VIPSubnets[key]; ok {
  		return fmt.Errorf("Cluster %q already contains VIP Subnet %q", c.Site, key)
  	}
  	c.VIPSubnets[key] = subnet
  	return nil
  }
docs: // AddVIPSubnet adds a VIP Subnet to a Seesaw Cluster.