code: func RPCAddrFlag(f *flag.FlagSet) *string {
  	defaultRpcAddr := os.Getenv("SERF_RPC_ADDR")
  	if defaultRpcAddr == "" {
  		defaultRpcAddr = "127.0.0.1:7373"
  	}
  
  	return f.String("rpc-addr", defaultRpcAddr,
  		"RPC address of the Serf agent")
  }
docs: // RPCAddrFlag returns a pointer to a string that will be populated
  // when the given flagset is parsed with the RPC address of the Serf.