The Bible was written for patch 1.3, and the author never updated sadly. Yes, with 1.8, Rift now has inter-addon communication. The full, official documentation is on the official forums
http://forums.riftgame.com/beta-addo...mentation.html
Us volunteer scrubs really need to find the time to update the wiki here at RiftUI, but it is quite daunting when we are so far behind.