Port priority (also known as controller slot priority) is a set of rules that determine the outcome of certain situations between characters, during matches. These rules are based on the numbered player ports (slots) in which each player plugs in, or occupies with his or her controller, and these are represented by P1, P2, P3 and P4 with respect to the first, second, third and fourth ports. CPU players may also occupy these ports, and are affected by port priority in the same ways as human players.