Transparent Content Negotiation in HTTP
HTTP allows web site authors to put multiple versions of the
same information under a single URL. Transparent content
negotiation (TCN) is an extensible negotiation mechanism, layered on
top of HTTP, for automatically selecting the best version when
the URL is accessed. This enables the smooth deployment of
new web data formats and markup tags.
- The transparent content negotiation specifications have been
frozen as experimental RFCs.
- There are currently three (known) server-side implementations.
- Feature tag registration procedures have been defined in an RFC.
The feature tags from the transparent content negotiation RFCs are
now officially called 'media feature tags'. A tag registry has been
set up, though at this time the 'global tree' registration mechanism
is not yet in place.
- The IETF has formed a Content Negotiation Working Group (conneg)
to cover content negotiation inside and outside of HTTP.
(Last updated 5 Jul 1999)
- Apache (starting version 1.3.4)
has server-side support for transparent content negotiation and remote
variant selection. Feature tags are not supported.
- The EmWeb embedded web server
architecture includes support for transparent content negotiation and
remote variant selection. Feature tags are not supported.
- SRE-http, a free HTTP/1.1
compliant web server for OS/2, implements transparent content
negotiation, and can do remote variant selection with its own custom
algorithm. Currently the implementation is in 'stable beta'. RFC2295
is supported from version 1.3g on, some earlier versions supported
pre-RFC2295 semantics. Feature tags are not supported.
Feature tag registry
IETF Content Negotiation Working Group