code: func ValidateRowPrintHandlerFunc(printFunc reflect.Value) error {
  	if printFunc.Kind() != reflect.Func {
  		return fmt.Errorf("invalid print handler. %#v is not a function", printFunc)
  	}
  	funcType := printFunc.Type()
  	if funcType.NumIn() != 2 || funcType.NumOut() != 2 {
  		return fmt.Errorf("invalid print handler." +
  			"Must accept 2 parameters and return 2 value.")
  	}
  	if funcType.In(1) != reflect.TypeOf((*PrintOptions)(nil)).Elem() ||
  		funcType.Out(0) != reflect.TypeOf((*[]metav1beta1.TableRow)(nil)).Elem() ||
  		funcType.Out(1) != reflect.TypeOf((*error)(nil)).Elem() {
  		return fmt.Errorf("invalid print handler. The expected signature is: "+
  			"func handler(obj %v, options PrintOptions) ([]metav1beta1.TableRow, error)", funcType.In(0))
  	}
  	return nil
  }
docs: // ValidateRowPrintHandlerFunc validates print handler signature.
  // printFunc is the function that will be called to print an object.
  // It must be of the following type:
  //  func printFunc(object ObjectType, options PrintOptions) ([]metav1beta1.TableRow, error)
  // where ObjectType is the type of the object that will be printed, and the first
  // return value is an array of rows, with each row containing a number of cells that
  // match the number of columns defined for that printer function.