Perhaps I might be blind, but if this was some sort of flag, I can't find it on Polygon.

Specifically, I want something like this: https://mirror.codeforces.com/gym/373765/problem/B where the only allowed "language" is ZIP.

I also have other concerns like how to write the checker/do scoring for it. Does anyone have a guide for how to go about this?

Many thanks in advance.