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Gets or sets the ValidationAlertStyle value that specifies the data validation alert style.
This property specifies which icon is shown in the validation error message box when invalid data is entered for the range.
ValidationAlertStyle AlertStyle { get; set; }
Property AlertStyle As ValidationAlertStyle
IValidation validation = worksheet.Range["A1"].Validation;
validation.Add(ValidationType.Whole, ValidationAlertStyle.Stop, ValidationOperator.Between, 1, 10);
ValidationAlertStyle alertStyle = validation.AlertStyle;