Plack::Middleware::Negotiate applies HTTP content negotiation to a the PSGI
manpage request. The PSGI environment key 'negotiate.format' is set to the
chosen format name. In addition to normal content negotiation one may
enable explicit format selection with a path extension or query parameter.
The middleware takes care for rewriting and restoring PATH_INFO if it is
configured to detect and strip a format extension. The PSGI response is
enriched with corresponding HTTP headers Content-Type and Content-Language
unless these headers already exist.

If used as pure application, this middleware returns a HTTP status code 406
if no format could be negotiated.