ABAP Rule: how to read data fields of other Autom.structures?

Hi!

I would like to implement an ABAP Rule for a certain field where I want to use the value of the migration field in the same migration object but in the other aut. structure.

With the use of $C$ placeholder like this: "$C$-MUSTER_KUN" ...I can only access data fields in the same autmated structure.

Thanks for your help!

Best regards,

Peter