How would I make R15 skinned avatars?

I’ve been messing around with skinned meshes and came across the new skinned avatar model. It’s R15, but the joints animate smoothly, without cracks.

Classic R15:


Skinned R15:

When looking at the parts, I noticed every body part had a WrapTarget, I’m not sure what that does but it has something to do with it.

I’d like to make a custom skinned R15 character, as these are ugly & I’d like my R15 animations to work with it. How would I make a skinned R15 avatar model? Any information/resources would be extremely helpful!