Now that I can finally build the docs locally I've started making some notes of things that seem like they could use clarification so I can submit some PRs to improve them. 

I'm hoping someone can help me find information on a couple of things:

CameraUi

• What do all the various mouse buttons control? As best I can tell: 
• Left button causes horizontal motion to rotate about the y-axis, vertical motion pitches in a polar orbit (not sure how best to describe that)
• Right moves the pushes in or out on the lookAt point
• On OS X Option clicking lets you pan around moving the lookAt point
• Is there a way to limit camera moves? Say keep the camera above the xy-plane? Or prevent them from pushing back beyond a certain point?
• Is it restricted to just using those axes? Is it possible to orbit a different axis? Yes it is, it uses the camera's initial world up vector as a basis for rotation. So you can just assign an alternate value to that before connecting the camera.
• How do you get let the app handle mouse event ahead of CameraUi? Rich points out that you can use a signal of -1 in this comment.

Geom::Plane

• Could we explain what axes()'s parameters mean? I wasn't familiar with the term axis-u and axis-v so had to do some experimentation