That is the index of you text you are comparing. codecombination is your text. The number after that tells tokenat where to look inside the text to compare that character.
So codeCimbination is a variable that equals "201"
The first character in that text is at index 0. So index 0 of the text "201" is eaul to "2", Index 1 would equal "0"
So what the code is doing is checking to make sure the frame of group A is the same as index 0 in this case "2", the frame in group B is the same as index 1 which is "0", and frame of group C is the same as index 2 which is "1"
You can read back on a post I wrote before in this thread that explains how tokenat works.