Masks are just containers that store painted values, they can be enabled and disabled so changes can be tested non-destructively. The mask target determines what those values will be applied to. “Backstop Distance” is a target. Right clicking on a mask allows you to set the desired target. If you look earlier on in thread I illustrated what backstops are and how they work.
For cloth on cloth we have no solution currently, layered clothing is complex and we don’t have a good solution for that at time. For a belt you could however just have a number of bones inside the belt that are simulated, and attach clothing collision objects to the bones. That will move the cloth away from the belt at runtime, but the cloth will never be able to apply force to the belt so you’ll need to tweak the constraints on the belt bones to not allow it to push too far.
Hopefully helps.
Benn.