I guess what I'm trying to say is that the logic in the merge node is where the magic happens. So you have parallel branches, A and B. A orders boxes while B orders shapes. Somewhere in A and B we created Box and Shape instances and those are outputs of A and B, respectively. The merge node, C, waits until A and B are completed and takes their outputs as input. The merge node needs to know how to match up the Box and Shape instances to say shape 2 can fix in box 1.
