I don't get it why some many developers WON'T use the real documentation. Heck, many of them WON'T even download from official sources, instead relying on third-party collections with obsolete versions, or, worse (at least potentially) intentionally hacked/poisoned mods.
WHY do so many use W3Fools? I once had a Google filter set-up to keep them out of search results. But W3Fools gamed Google with dozens or hundreds of of different domains, until the technique became widespread and Google threw in the towel and removed the filter feature. W3Fools is the WORST possible place to get accurate information. I half-suspect it is actually a Russian or Chinese initiative to spread absolute crap all over the Internet. Find out where W3Fools is blocked. That will tell you who is behind it!
MDN is a GREAT site for learning HTML/CSS/JS. The jQuery Learning Center is a GREAT site for learning jQuery. Why do so many flock to tutorial sites with horrible quality and WRONG information?
I don't use PHP, so don't know if the official documentation is GREAT. I have to guess, though, that after all these years, it can't be totally awful.
(Last time I used PHP was like a year after it first appeared. I think I had it emailed to me by the author. I feel for the author, who is probably blamed by many for it's failings. It was just a simple script to help him with his blog site, and he was an amateur. I do not mean "amateur" in a disparaging way, I mean it in a descriptive, literal sense. Others took it up and built crap on top of a simple script with a simple purpose. Along the way, there's been a corrective course that turned it into a language with a not-completely-awful syntax, but the developers haven't had the will to remove the awful parts. It seems impossible to get PHP developers to stop cutting-and-pasting, and to stop using the awful parts.)
CODE DOES NOT BELONG IN HTML TEMPLATES. CODE DOES NOT BELONG IN HTML TEMPLATES! CODE DOES NOT...
Unfortunately, that's how MOST PHP sites are written.