code: func (nc *Conn) createRespMux(respSub string) error {
  	s, err := nc.Subscribe(respSub, nc.respHandler)
  	if err != nil {
  		return err
  	}
  	nc.mu.Lock()
  	nc.respMux = s
  	nc.mu.Unlock()
  	return nil
  }
docs: // Create the response subscription we will use for all
  // new style responses. This will be on an _INBOX with an
  // additional terminal token. The subscription will be on
  // a wildcard. Caller is responsible for ensuring this is
  // only called once.