code: func ValidateStartEndOptions(start uint64, end *uint64) Validatable {
  	return func() error {
  		if end == nil {
  			return nil
  		}
  		e := *end
  		if start > e || e > start+MaxIndexDiff {
  			return ErrInvalidStartEndOptions
  		}
  		return nil
  	}
  }
docs: // ValidateStartEndOptions validates the given start and optional end option.