The FAA "writes" a master MEL for each aircraft which then gets tweaked and approved by the FAA for each particular airplane based on what's actually equipped.

So things on the list should be relatively uniform across aircraft types and companies. A carrier can go more strict than the FAA, but never more leniant.

I stress againt I haven't looked it up, because I don't have a MEL book at home, but for example;
The FAA MEL might say that an aircraft being dispatched with an inoperative lav is restricted to legs no longer than 60 min.

The carrier can then restrict that further to something like 45 min, but never go beyond 60 min.

Just simplified, because there would be a whole bunch of other things to do as well, but that doesn't really need to be addressed for the purposes of this discussion. (Placarding, Maintenance paperwork, etc...)