The book series (6 of them) is drafted, and to some extent edited, on GitHub. What you see is what you get.

There are some edits and refinements that happen to the content during the publishing/production phase at O'Reilly that aren't necessarily appropriate to back-port to the repo. But I do try to get most of the main substance stuff sync'd.

The free GitHub repo versions of this content represents the drafts of the books in the mostly complete stage, whereas the published books (digital or print) are the final, final versions.