My only complaint with the guide so far was that it was historically presented as a single huge DokuWiki page with ambiguous heading structures (probably because the page was made of several other pages, each having top-level headings by its own). The current version looks much cleaner!

100% agree. I think what stood out to me the most was that it did explain a lot of the decision making. I feel like often other docs don't explain the decisions that did go into their software at all

This is also what sets good code comments and code level API documentation apart - explaining the reasoning and intention for both implementation and for intended use. Essentially the why and how, not that what...

Even more impressive is that Pieter put the same attention into documenting the 0mq community's social architecture, as well: https://hintjens.gitbooks.io/social-architecture/content/