DataValidationCollection.Add(CellRange, DataValidationType, ValueObject) Method
Creates a new data validation entry and adds it to the document's collection.
A CellRange object that is the worksheet range to which the data validation rule is applied.
A DataValidationType enumeration member that specifies the validation type.
A ValueObject that is the value used in the criterion.
A DataValidation object that specifies a validation rule for a worksheet range.
For the DataValidationType.Custom type, the criteria is a string which can be recognized as a worksheet formula. Therefore, it must begin with an equal sign and evaluate to either true or false.
An individual worksheet cell can have only one data validation rule associated with it. If subsequent Add method calls affect the same cell, only the data validation rule created in the last call is applied.