What is the difference between CONTROL_MODE_PD and CONTROL_MODE_POSITION_VELOCITY_PD ?

[ManifoldFR]

In PyBullet, the implementation of the setJointMotorControl2/MultiDof functions seem to be implemented the same whether CONTROL_MODE_PD or CONTROL_MODE_POSITION_VELOCITY_PD are set, as the case statements inside of the switch cover both modes (see here):

case CONTROL_MODE_POSITION_VELOCITY_PD:
case CONTROL_MODE_PD:

There's the exception for setJointMotorControlMultiDof (not the array version) where CONTROL_MODE_PD triggers an error.

I don't see any difference in SharedMemory/b3RobotSimulatorClientAPI_NoDirect.cpp either. However, it seems the behaviour of the joints is not the same. What is the actual difference?