How does the Mazda rear disk brake handbrake auto adjust mechanism, inside the brake piston, work?

I have taken a piston apart, as for as I can, but I still cannot fully understand how it works.

I can understand that the piston is not simply screwed onto the handbrake push-rod, because if it were, then every time the footbrake was applied, this would push the piston out to press the pads against the rotor, and the handbrake push-rod would be pushed back against the handbrake cam. Then when the footbrake was released, the brake pads would still be pushed against the rotor, and the brakes would still be applied, by the screw thread. There is actually a torsion spring inside the piston, which, I think, backs off the screw thread by about ten degrees every time the footbrake is released, to release the brake In addition, when the footbrake is applied, the piston cannot rotate to take up the handbrake backlash, because it is pressed against the back of the brake pad. Instead, there is a separate nut inside the piston, which rotates instead of the piston rotating.

Can anyone explain how this mechanism is put together, and how it works?