Bob,
Currently jetty doesn't have any particular support for content negotiation.
However, this could potentially be done as a RewriteHandler rule, which would be pretty simple in some respects as such a handler would have access to the code that already exists in Jetty to evaluate quality based header values to give an iteration of acceptable content types. However, if the RewriteHandler is installed before a context, then it would not be able to easily ask if a resource exists or not (which may not be able to be asked if the resource is dynamic).
You could also do it as a Servlet Filter, which would have access to the context resource base, but would have to copy the code to evaluate the quality values.
While we have never really had any demand for Content-Negotiation, if somebody was to contribute either a Rule or a Filter, then we be happy to include it in future releases. Also very happy to answer questions if you want to have a shot at writing such a rule and/or filter.
This is the quality list method.... which is actually ancient code using Enumeration (because of Servlet spec).... hmmm really should be updated and moved to HttpField class.... I'll do that in the next week or so.
cheers