StephenA, this is a great idea!
"XX" in most other technical areas is used as a representative for any other number or letter. For example, If GM sent out a recall for all trucks with a VIN (Vehicle Identification Number) of 1K50087506UV56-xxx, it would mean ALL vehicles whose VIN started with 1K50087506UV56, no matter what the last 3 letters or numbers were. Usually the X's are in the opposite case and/or italics, and can replace ANY letter or number.... & that's my 2 cents worth.
\'99 GMC K3500 CrewCab Dually, mostly stock \"But Honey, it\'s SUPPOSED to smoke & rattle!\"