CSER rule example between parent and child. If segment 10 on parent = y, then segment 25 on child

I am trying to find an example of a CSER rule that works between a parent segment and an assembly of that parent with another segment.   If parent segment 10 = "Y", then populate segment 25 on child with '01'    How do I move between parent and assembly in cross segment editing rules?  I can find no example in JDE documentation.