text/html
  text/html;version=2.0
  text/plain
  image/gif
  image/jpg

=item content-encoding

This is one or more content encodings that has been applied to the
variant.  The content encoding is generally used as a modifier to the
content media type.  The most common content encodings are:

  gzip
  compress

=item content-charset

This is the character set used when the variant contains text.
The charset value should generally be C<undef> or one of these:

  us-ascii
  iso-8859-1 ... iso-8859-9
  iso-2022-jp
  iso-2022-jp-2
  iso-2022-kr
  unicode-1-1
  unicode-1-1-utf-7
  unicode-1-1-utf-8

=item content-language

This describes one or more languages that are used in the variant.
Language is described like this in F<draft-ietf-http-v11-spec-00.ps>: A
language is in this context a natural language spoken, written, or
otherwise conveyed by human beings for communication of information to
other human beings.  Computer languages are explicitly excluded.

The language tags are defined by RFC 3066.  Examples
are:

  no               Norwegian
  en               International English
  en-US            US English
  en-cockney

=item content-length

This is the number of bytes used to represent the content.

=back

=head1 ACCEPT HEADERS

The following Accept* headers can be used for describing content
preferences in a request (This description is an edited extract from
F<draft-ietf-http-v11-spec-00.ps>):

=over 3

=item Accept

This header can be used to indicate a list of media ranges which are
acceptable as a response to the request.  The "*" character is used to
group media types into ranges, with "*/*" indicating all media types
and "type/*" indicating all subtypes of that type.

The parameter q is used to indicate the quality factor, which
represents the user's preference for that range of media types.  The
parameter mbx gives the maximum acceptable size of the response
content. The default values are: q=1 and mbx=infinity. If no Accept
header is present, then the client accepts all media types with q=1.

For example:

  Accept: audio/*;q=0.2;mbx=200000, audio/basic

would mean: "I prefer audio/basic (of any size), but send me any audio
type if it is the best available after an 80% mark-down in quality and
its size is less than 200000 bytes"


=item Accept-Charset

Used to indicate what character sets are acceptable for the response.
The "us-ascii" character set is assumed to be acceptable for all user
agents.  If no Accept-Charset field is given, the default is that any
charset is acceptable.  Example:

  Accept-Charset: iso-8859-1, unicode-1-1


=item Accept-Encoding

Restricts the Content-Encoding values which are acceptable in the
response.  If no Accept-Encoding field is present, the server may
assume that the client will accept any content encoding.  An empty
Accept-Encoding means that no content encoding is acceptable.  Example:

  Accept-Encoding: compress, gzip