[9fans] Different representations of the same file/resource in a synthetic FS

[Roman V Shaposhnik <rvs@sun.com>]

Working on a RESTful API lately (which is as close to working on a 9P
filesystem as I can get these days) I've been puzzling over this issue:
is content negotiation a good thing or a bad thing? Or to justify
posting to this list: what would be the proper 9P way of not only
representing different "renditions" of the same information in
a synthetic filesystem but also give consumer a chance to declare
*a set* of preferred ones.

Lets assume a classical example (modified slightly to fit 9P):
a synthetic filesystem that serves images from a web cam.
The very same frame can be asked for in different formats
(.gif, .png, .pdf, etc.). Is serving
   /<date>/<time>/<camera-id>/gif/frame
   /<date>/<time>/<camera-id>/png/frame
   ...
   /<date>/<time>/<camera-id>/pdf/frame
and relying on reading
   /<date>/<time>/<camera-id>
for the list of "supported" representations really better
than what HTTP content negotiation offers?

Thanks,
Roman.