For anyone who doesn't understand, in the VARIABLES section, a "buttonpress" variable is made with a default value of 0, which makes the variable be 0 at the start of a level.
In the RULES section, if Button and Player are on top of each other, then the "buttonpress" variable is set to a value of 1.
The 2 rules below act if the "buttonpress" variable is a set value (so if buttonpress is 1, then every Door becomes an OpenDoor, and if buttonpress is 0, then every OpenDoor becomes a Door.)