Why the max_effort value equal to stiffness?

In omniverse, I import a robot, when I get the DofProperties, I see the max_effort value equal to stiffness, is this right?
another question is I can’t find the max_effort setting in IsaacSim UI Property, , is this right?
print the DofProperties I got follow infos:
image
we can see the fifth column is zero, but I get the stiffness value wthen I use self._articulation_controller.get_max_efforts()