When an ACTION is performed, the SYSTEMTRIGGERS the PROCESS AFTER INPUT event.The data passed includes field screen data entered by the USER and a function code.
A function code is a TECHNICAL name that has been allocated in a screen Painter or Menu Painter to a menu entry, a push button, the ENTER key or a function Key of a screen.
An internal work field (ok-code) in the PAI module evaluates the function code, and the appropriate action is taken.