Documentation and examples for ThreeJS.org are complete. There are a lot of contributors who are always adding material. In the world of simple-VR, there is the StereoEffects for rendering. This is an effects that renders the scene into left/right eye split-screen.
This set of examples will use the first scene. It is real simple (in terms of elements), but it is sufficient to illustrate the projection issues. For the purposes of this discussion assume that the display screen is sufficiently large to show everything that is desired to be displayed. Also assume that the rendering software does not enlarge the displayed scene to fit the screen.
For the last nine months I have been working on a declarative language for VR/AR/MR to display 3D content in a browser. I have called the language XSeen.
The importance of examples in learning a new language cannot be overstated. This section contains illustrative examples of using XSeen. As has been discussed there are a number of similarities between XSeen and A-Frame and X3D. These will be obvious in the examples. It is possible to intermix tags from each language in a manner that makes sense.