Getting started?

I'm trying to learn my way around the pubsub protocol, and having some 
difficulty. I'm interested in the protocol itself, and in using it in 
an application, i.e. not in a web browser. The main protocol document
	http://www.mod-pubsub.org/kn_docs/pubsub_protocol.html
seems to assume the reader already knows how the architecture works, 
and launches directly into the minutae of syntax and schema. Other 
documents seem to be aimed only at using the JavaScript library from a 
web application.

Is there some kind of document that describes the overall design of the 
protocol, that I could peruse first?

--Jens