Earlier quoted context omitted.
Wow, what a really mean-spirited comment, and it's the top one (at the time of writing.) -- did you consider what you said here before writing it? Let me propose a rewrite:- 'If you can't afford to buy this, the official emacs GNU documentation is great - [link]' Instead you first admit you haven't read it, then imply, but in somewhat weasel words, that it doesn't offer anything beyond what the official documentation…
Actually, good technical writing is among the most reliably lucrative genre of writing. That might not be saying much, but how many people make money writing poetry or genre fiction?
Ha that's a good point ;) but once you factor in opportunity cost for developers, especially ones experienced enough to write a book, it's definitely not a great choice (likely negative.)