Ludwig's Fingers - Attaching the Mesh


In terms of the fingers of the Ludwig RIG, I think I’m beginning to understand the use of Action Constraints. But I can’t seem to figure out how the finger portions of the MESH are being controlled by the finger bones. I notice that the “Deform Options” include “Vertex Group” and “B-Bone Rest”, but I can’t find any vertex groups except face related ones. And I still don’t understand the B-Bone option. Can anyone give me a helpful note on where to look for the answer?

Thanks so much!