some of the scripts i am seeing use self.session.props... whereas others just use session.props... what is the differentiator and where do i find it in the manual? i tried looking for self.session but got no results. is it similar to the JS this? i vaguely remember something about self in the IU courses, but do not recall which lesson it's in. 
Every Perspective element (available at self in component level event scripts and custom methods) has an automatic reference to the parent session, because a component can't exist without a session.
Self is just the Python convention for the instance that holds the method. JS, Java, various others call it "this".
'session', by itself, would only work in certain session event scripts. It should be pretty clear what's being delivered to you explicitly in whatever Perspective script you're authoring by the extension function UI.