w3fools is one of those stupid sites that exists sorely as a protest against the existence of another site.
It's written by the kind of people who used to recommend "validating" your HTML because then it would be valid. Yay!
The pedantry against w3schools is unhelpful, misguided and at times down-right wrong.
For example:
w3schools: "URLs cannot contain spaces. URL encoding normally replaces a space with a + sign."
w3fools: "That's not true. An URL can use spaces. Nothing defines that a space is replaced with a + sign"
Actually: "The encoding used by default is based on a very early version of the general URI percent-encoding rules, with a number of modifications such as newline normalization and replacing spaces with "+" instead of "%20". The MIME type of data encoded this way is application/x-www-form-urlencoded, and it is currently defined (still in a very outdated manner) in the HTML and XForms specifications. In addition, the CGI specification contains rules for how web servers decode data of this type and make it available to applications."
http://en.wikipedia.org/wiki/Percent-encoding#The_applicatio...
Many (most) of these things are judgement calls and/or historical anomalies. W3Fools is wrong to say w3schools is a problem - it is merely insufficient on its own. They would be better off generating a better version rather than complaining.