Being given correct information but making mistakes, and then learning from those mistakes in your efforts to recreate the good advice, is a useful learning technique.

Being given incorrect information, and making mistakes, and not knowing you've made mistakes, is not a useful learning technique.

And while these people are making mistakes and learning from them their customers are suffering buggy code and everything that goes with that - data loss and insecurity at the extreme end and unexpected behaviour at the mild end.

> "Being given incorrect information, and making mistakes, and not knowing you've made mistakes, is not a useful learning technique."

W3Schools has pointed out that users take a risk with its content, and it made no claim over the quality of its code. The only element they have authority over is its clarity, and that is what's important. The information may be lacking, but I stick by my guns when I say that crap code can still make some concept that a tutorial revolves around clearer. If other elements are not relevant to the tutorial, I do not believe it is fair to blame the author for excluding them.