How are the function code handles in Flow Logic? | ABAP Module Programming

- When the User selects a function in a transaction ,the system copies the function code into a specially designated work field called OK_CODE.This field is Global in ABAP/4 Module Pool.The OK_CODE can then be evaluated in the corresponding PAI module. The function code is always passed in Exactly the same way , regardless of Whether it comes from a screen’s pushbutton,a menu option ,function key or other GUI element.