Sending of cookies (and other headers) with request

One important piece missing in the HTTP request header section is that the browser has a bit of logic around figuring out which cookies, if any, to send along with the request. There's also a ton of extra logic around the compression, language, mime-types, user-agent and so on which are worth mentioning in the request section, and then calling out in the response section: in general, both HTTP servers and application layer handlers look at bits of the header to modulate the response.