The following shailo was asked.
A sofer had klaf that had a small tear in the middle. The tear made a sort of square that on 3 sides it was torn and one side still attached. Imagine a sort of "window" that could be opened and closed in the klaf. May such a part of the klaf be written on (without fixing it with a matlis of some type -- if it could be fixed.) As well if it's already written on what's the din?