# AA and AB Rules

When the numerical value exceeds 26, a combination of letters is produced. The letterStyle specifies how letters are combined. If AA is specified, then the letters are repeated. If AB is specified, then the letters accumulate in a fashion similar to that of an odometer. Specifically, the revision number is first converted to a base-0 index, and then converted to a base-26 number.

When AA is specified, then the lowest base-26 digit is used as a 0–based index to select a letter, and that letter is repeated as many times as the number is a multiple of 26, plus 1.

When AB is specified, then the highest base-26 digit is decremented, and each base-26 digit is used as a 0–based index to select a letter. (If letters are omitted, then the base will not be 26, but the number of letters that remain in the alphabet.)

See the table for examples.