Most languages support concatenation of strings using the + operator. The only mainstream languages I can think of that don't are PHP (which uses ".") and low-level languages like C & C++.
My brain is too mushy to do it myself right now, but I wonder what the result would be if we were to consider the alphabet a base-26 number system and added the numbers that correspond to those letters.
Honestly dodged a bullet there when they can’t even get their errors straight. Obviously an undefined variable you and me would be more appropriate. Duh. 👯♀️