How are the function code handles in Flow Logic?
When the User selects a function in a transaction, the system copies the function code into a specially designated work field known as 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 similar way, regardless of Whether it comes from a screen's pushbutton, a menu Option, function key or other GUI element.