I mean, I am by no means an expert in PHP, and in fact most of my knowledge of it comes from hating on it (or having been thrust into the unfortunate position of being the system administrator for a popular MediaWiki instance), but even in my limited experience with it from a couple lifetimes ago I know that most of the documentation for PHP is crowdsourced in the documentation comments section. That might be depressing, but that isn't what that comment was defending: it does feel likely to be true that there aren't many "unknown unknowns" waiting for you in PHP.