code: func compareListValuesAtIndex(list1Inbounds, list2Inbounds bool, list1Value, list2Value string) (interface{}, interface{}) {
  	bothInBounds := list1Inbounds && list2Inbounds
  	switch {
  	// scalars are identical
  	case bothInBounds && list1Value == list2Value:
  		return nil, nil
  	// only list2 is in bound
  	case !list1Inbounds:
  		fallthrough
  	// list2 has additional scalar
  	case bothInBounds && list1Value > list2Value:
  		return nil, list2Value
  	// only original is in bound
  	case !list2Inbounds:
  		fallthrough
  	// original has additional scalar
  	case bothInBounds && list1Value < list2Value:
  		return list1Value, nil
  	default:
  		return nil, nil
  	}
  }
docs: // If first return value is non-nil, list1 contains an element not present in list2
  // If second return value is non-nil, list2 contains an element not present in list1