Use the IN array operator to determine if a field value is in a list of other values.
Example: x in [y]
   This checks tosee if x is in array y.
Example: {customer.Region} in ["CA", "HI", "AK"]
   Is the value of {customer.Region} field in the array of state abbreviations.

How to use the NOT IN logic.
Example:  NOT({customer.Region} in ["CA", "HI", "AK"])
   Is the value of {customer.Region} field NOT IN the array of state abbreviations.