You can define a function module as processing method for a symbol by choosing one of the following options:
The entry in WWI has priority.
The function module must meet the requirements of a specific interface. The system checks both in Customizing as well as when you use a method in layout, whether the function module is active in the system and whether it meets the requirements of the interface.
Before creating new function modules, check the documentation of sample function module
Choose transaction
se37 and enter the name of function module C128_DUMMY_CONVERSION_METHOD .You can now display the documentation and the source text for the interface of the function module.