code: func argInfo(cb Handler) (reflect.Type, int) {
  	cbType := reflect.TypeOf(cb)
  	if cbType.Kind() != reflect.Func {
  		panic("nats: Handler needs to be a func")
  	}
  	numArgs := cbType.NumIn()
  	if numArgs == 0 {
  		return nil, numArgs
  	}
  	return cbType.In(numArgs - 1), numArgs
  }
docs: // Dissect the cb Handler's signature