code: func (h *HumanReadablePrinter) Handler(columns []string, printFunc interface{}) error {
  	printFuncValue := reflect.ValueOf(printFunc)
  	if err := h.validatePrintHandlerFunc(printFuncValue); err != nil {
  		glog.Errorf("Unable to add print handler: %v", err)
  		return err
  	}
  	objType := printFuncValue.Type().In(0)
  	h.handlerMap[objType] = &handlerEntry{
  		columns:   columns,
  		printFunc: printFuncValue,
  	}
  	return nil
  }
docs: // Handler adds a print handler with a given set of columns to HumanReadablePrinter instance.
  // See validatePrintHandlerFunc for required method signature.