It's like how they have hamburger restaurants, where you can ask for a hamburger without the pickle, instead of having hamburger without pickle restaurants. C is the burger, bacon, bun, lettuce, tomato, onions and sauces, and ++ is the pickle.
"Oh, you wanted mayo on your burger? We can do that, but you also have to have mustard. Don't worry, you won't have to pay for it.. but it's going to be in there."