HTTP for HTML Authors, Part II
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Software version info
Another two very useful HTTP headers that are used very often are Server and User-Agent. These two are used in the reponse and request, to specify the product name and version of the Web server and the user agent respectively. Neither of these fields is mandatory, and in fact they are often omitted, but they do sometimes give useful information.
As you might imagine, having experienced the chaos that is the Web today, a lot of people have thought of using the User-Agent header to dispense different documents depending on the browser in order to satisfy the numerous bugs and incompatibilities in popular browsers. Of course, before you know it, browser makers detested this attempt at setting right their wrongs and started imitating each other's User-Agent headers in order to convince Web servers that they where, in fact a different browser, so as to show that they are compatible with the latest and greatest. Unfortunately the browser makers forgot to make their browsers compatible with anything, and hence this nice and reliable way of working around browser bugs went the way of the Dodo. Although most modern browsers have stopped this despicable masquerading, looking at the User-Agent field is still a poor way of judging what a user agent is capable of.
The Server field is of less direct practical importance, and is mostly used by people like NetCraft to gather statistical information about software usage on the Web. Again, this is an optional header and many Web servers refuse to let the world know what version of which software they're running.
