Mate a Component of a Rigid Sub-assembly to a Component of the Top-level assembly

A question came in recently about constraining a moving component of a SOLIDWORKS rigid sub-assembly to a component of the top-level assembly.  The sub-assembly was fully constrained in the top-level assembly, so a mate between sub-assembly component and another component in the top-level assembly would not work.  The sub-assembly was also not suitable as flexible, it had to remain rigid.

SOLIDWORKS Rigid Sub-assembly

I brought up this question as a reminder that top-down or in-context modeling does not end with the placement of sketch planes and in-context relations or equations.  In this case:

1. The sub-assembly was edited within the top-level assembly.
2. A plane was created based off a component of the main assembly.
3. The moving part was then constrained with respect to that plane.
4. The mate was created in the sub-assembly.
5. But the reference plane was defined in context of the top-level assembly.