I checked into Hartzell’s stuff awhile back but never bought the book. If you go to the website you can watch the videos and find a bit of information.
From what gathered his premise is the ankle tightens up and immobilizes to protect ligaments while they heal from overstretching and tears. His technique is to mobilize the ankle right away and by doing so the protective mechanism will relax and pain and tightness will lessen. The protective mechanism is strong so you can’t just start moving the ankle so he uses joint distraction using jump stretch bands to open space in the joint which allows more movement.