I'll need to do some surgery on the rendering of the navigation to make this look sensible.
Currently, the User Handbook part of the Jenkins User Documentation only supports 1 level of depth (as you can see from this link).
It would be great if we could implement 2 levels of depth (i.e. a hierarchy of 3 levels).
The FreeBSD Handbook, which is loosely how we're aiming to structure the Jenkins User Handbook documentation on, is based on a hierarchy of 3 levels.