How to constrain camera pitch?

CesiumJS
1

I would like to constrain the pitch of the camera, I have been playing around with the camera constrainedAxis:

2

Maybe you can find some info in this topic: https://groups.google.com/forum/#!searchin/cesium-dev/tilt/cesium-dev/Pjrjw9asXns/rhgLXXSahrgJ

Willem