It is not depending on settings of clients nor is it magic. The HTTP headers are as much part of the input of a request as the url itself. The only difference i

It is not depending on settings of clients nor is it magic. The HTTP headers are as much part of the input of a request as the url itself. The only difference is that most people aren't aware of the http headers and they aren't shown by default in the browser. But not displaying information that isn't relevant to this context is not the same as magic. This isn't a problem either - if you are a regular internet user, then stuff just works and you don't need to know about http headers at all. If you are a (web) developer, you really should have a general idea about http headers and what kinds of things they are useful for - and then its not magic anymore.