The video below actually details it all quite well, but i’ll also add a few pictures and a description below.
So, the idea is to move the X motor off the carriage. One immediate benefit is that the size of the entire X axis is no longer constrained by the size of the motor, perhaps leading to more compact designs? It would be interesting to try out a vertical X axis design with this setup.
Anyway, the X motion is transferred to the belt via a square extrusion rod which drives a cog which sits directly on it. This rod slides through the mount and cog during Z motion. The belt in this design is within the two X smooth rods, but other layouts could be adapted to move the belt to the outside (as with the original Huxley I believe). In this design the hot-end would either have to fit through the belts, or hang over the edge of the rods. Again, here the vertical layout would be interesting.