Validations and Multi-Valued Fields 

The value of a multi-valued field may consist of one or more lookup values. Similarly, the value of a multi-valued text attribute may consist of one or more attribute text values.

When you define a validation expression, you can test the value of a multi-valued field or text attribute for equality to a constant value by: (1) choosing the “=” operator from the drop-down list of operators; and (2) choosing one or more constant values from the pop-up dialog of legal lookup values or attribute text values.

When you test a multi-valued field or text attribute for equality to a value or values, “=” means “identically equal” (that is, the same set of one or more values in exactly the same sequence).