Thanks for those two links. They hilghlight some of the quirks. One of my biggest WTF moments of UE4 is covered in that FAQ:
Y axis up.
X - left, right
Y - up, down
Z - forwards, backwards
Z axis up.
X - forwards, backwards
Y - left, right
Z - up, down
Everywhere else in the entire computing world Z is depth. UI windows have a z-order, or depth. 3D z-buffers are depth.
I've wondered what kind of shrooms they were on when they decided those. It isn't the traditional orientation. They cannot even use the excuse of a top-down view since Y and X are transformed for that viewpoint as well.
Quake had Z as up. Blender has Z as up. 3DS Max used to be Z up.
I think the 3DS MAX being up is the culprit that caused the historical Z up used by IDTech and Unreal and also Blender. The reason 3DS Max used up is because it used the same interface as early CAD packages which always had X/Y along the ground plane because this is the way it is done in architectural plans and maps.