Schulz was interested in very wide ratio designs, even providing for the, very modern, ability to handle a 40 tooth rear sprocket. His derailleur used a pulley cage that, like the 1970s Huret Duopar, had two independent pivot points. This allowed the guide pulley the freedom to more closely track the profile of the freewheel, maintaining an even chain gap. Very cunning.
This design also appears to incorporate a latch mechanism that can catch the derailleur and restrict its movement (part 80 in the diagram above). Frank Berto claims that this latch was used, when the bike was parked unattended, to stop curious onlookers from being able to damage the gears by fiddling with the lever. We have all been there.