http://spywareitdaiuyfo2sqb5vsg7mek5cjabdr73luhnda57t2hyuzg7yyd.onion/articles/http.html
Even though this is a good section, it shows a very naive viewpoint from the W3C, the expectation that this feature would not be abused, and the expectation that implementers of this standard would respect the privacy of their users and would not use these features of the protocol to datamine users.