Questions for a few conflicting infos I would like put to rest about root motion.

Before I start out with my new rig and animations from max to UE4 I would like to know a few things about root motion from anyone out there who is willing to help.

1- The root bone at 0,0,0 cannot move Z up or down they say, later while asking about climbing or jumping, someone wrote that they could allow the root bone to move up Z but not Z below floor level and that this was successful for climbing animations, is this correct?

2 - What if the character jumps down from a small cliff, or goes down stairs how’s that going to be possible with root motion if the root cannot be animated going below floor level?