The file says this,

------
; If you find a chord that BB won't accept like Csus2, when it expects C2 instead
; you can enter this on a single line (without the quotes) "Csus2@C2"
; Then BB will enter the chord C2 if you type in Csus 2.
; these allow someone to type in Csus2 and the program will accept it.
------

Why do they give an example that has absolutely no effect? The file says "Then BB will enter the chord C2 if you type in Csus 2." but BIAB does this regardless of whether or not you enter that into the file! A useful example would make this easier to understand!