Download REAPER Plus! The Power of SWS Extensions (7MB PDF) for extension version v1.7.1. The new version of SWS, v2.1, has a few features that are not included in this version of the manual, but the manual is still mostly accurate.
Geoffrey Francis, of the REAPER user manual fame, (and user "nicholas" on the forums) has been so kind as to write a manual for the SWS extension. The manual is available from the link above in electronic-only PDF format. If you want to print the PDF, or would like a copy of the manual shipped to your door, please support Geoff and purchase a copy at his Lulu store. While you're there, make sure you check out his other books, Up and Running, A REAPER User Guide, and ReaMix: Breaking the Barriers with REAPER.