Some games need more buttons than a gamepad can handle, or some games need a button that is used only once in the game. You can add “extra buttons” that will be displayed on the screen. When pressed, they can send a key press or a gamepad button press.
For example, the game Rescue on Fractalus for Atari needs many buttons; it’s a game designed to be used with a keyboard. Although there is a gamepad mapping for this game, it’s easier to play using extra buttons containing the real action names.
This is the extra button definition for Rescue on Fractalus:
Land = BTN_A Fire = BTN_B Sys = BTN_X Ship = BTN_Y TH- = BTN_TL TH+ = BTN_TR Door = BTN_TL2