GET /models/SomeModel.xml HTTP/1.1 Host: www.example.org Accept: application/cellml-1.0+xml; q=0.5, application/cellml-1.1+xml; q=1
HTTP content negotiation was one of those "nice in theory" protocol additions that, in practice, didn't work out. The original theory of content negotiation was worked out when the idea of the web was that browsers would support a handful of media types (text, html, a couple of image types), and so it might be reasonable to send an 'accept:' header listing all of the types supported. But in practice as the web evolved, browsers would support hundreds of types of all varieties, and even automatically locate readers for content-types, so it wasn't practical to send an 'accept:' header for all of the types. So content negotiation in practice doesn't use accept: headers except in limited circumstances; for the most part, the sites send some kind of 'active content' or content that autoselects for itself what else to download; e.g., a HTML page which contains Javascript code to detect the client's capabilities and figure out which other URLs to load. The most common kind of content negotiation uses the 'user agent' identification header, or some other 'x-...' extension headers to detect browser versions, among other things, to identify buggy implementations or proprietary extensions. I think we should deprecate HTTP content negotiation, if only to make it clear to people reading the spec that it doesn't really work that way in practice. Many people seem to use HTTP content negotiation as a motivation for adding 'version' parameters to MIME types or registering new MIME types, with the hopes that the MIME types or parameters would be useful in HTTP content negotiation, and we should warn them that it isn't really productive to do so. That's why it might be useful advice to add to the guidelines for registering MIME types, should those ever be updated. (I think this situation is mainly my fault, fwiw, so: I'm sorry). Larry