code: func (f *FlagSet) IP(name string, value net.IP, usage string) *net.IP {
  	p := new(net.IP)
  	f.IPVarP(p, name, "", value, usage)
  	return p
  }
docs: // IP defines an net.IP flag with specified name, default value, and usage string.
  // The return value is the address of an net.IP variable that stores the value of the flag.