Thank you for your reply. What I'm looking for is C# API documentation. Are you suggesting to refer to the source codes (C# scripts) in the Unity Modules because the documentation doesn't exist? If so, any idea about when it'd be available?
Also, as you showed the link to a forum thread, I see one of the message there says "Orion has all things gestures, tools and pointables removed. other than that it is pretty much the same as before." Does it mean this old API documentation is still useable?