How does the mechanism in a switchable socket wrench work?

Pretty simple, but having a bit of trouble finding more info on it, how does the mechanism on a switchable socket wrench (the kind where you flick a lever, or turn a dial on the back of it) work so that it changes the direction that it ratchets in? I am guessing there are two oppositely toothed rings, but I am curious as to how the lever/dial switches it over.