Kite,
You are right. Documentation was definitely a weak point at one time. Many functions you just had to ask around for help. Very frustrating. This is one of the things that has changed for the better, and Reaper is about the best documented DAW out there currently. Big change from several years ago, and probably born out of necessity to understand anything under the hood.
The internal manual is well over 400 pages and updated almost as fast as the program. The site now also references a comprehensive library of support videos, tutorials, PDF documents. Sections for supporting extensions, themes, scripting tools.
http://www.reaper.fm/userguide.phpCheck out especially the Reaper 5 Explained video series. Free now. I paid $50 for the ver 4 series. Had used the program for almost 10 years and a few minutes thru the first video, realized that I’d only scratched the surface.
http://www.reaper.fm/videos.phpOf interest to Sonar users, look at this. Gives some comparative info as to what is missing in either and how common tasks are done.
http://www.reaper.fm/guides/SONARtoREAPER.pdfThen of course the tons of YouTube videos and several commercial publications.
John