https://github.com/ncoghlan/python-userref/blob/master/ODF/Chapter01_EssentialConcepts.odt is the Chapter 1 userref link now that the PSF SVN server has shut down.

Depending on what you mean by "Pursuing this...":

1. I'd definitely still love to see the content from the user reference converted into a collaborative documentation project and brought up to speed with modern Python - it's just a large enough task that I've shied away from doing it myself.

2. For this ticket itself, I'm thinking this kind of explanatory material might find a better home in the Developer's Guide these days, as there it could also provide pointers to the different parts of CPython that implement each phase.