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Gets whether all the validation criteria are met (that is, if the range contains valid data).
This property returns true when the current value in the validated range satisfies
the configured validation settings. If no data validation is applied to the
range, this property returns true.
bool Value { get; }
ReadOnly Property Value As Boolean
IValidation validation = worksheet.Range["A1"].Validation;
validation.Add(ValidationType.Whole, ValidationAlertStyle.Stop, ValidationOperator.Between, 1, 10);
worksheet.Range["A1"].Value = 5;
bool isValid = validation.Value;