how to use heuristic SAP_PP_012?

Hi,

We have a requirement to propagate the priority from finished good planned orders to semi-finished good orders. Can sombedy please explain how heuristic SAP_PP_012 can be used for this purpose? Is it executed as a heuristic run step or should it be called from an MRP heuristic like SAP_MRP_001? We are in a make-to-stock environment.

Any suggestion is highly appreciated!

Regards,

Peter