from-webmachine.erl

decision(v3c3) ->
    PTypes = [Type || {Type,_Fun} <- resource_call(content_types_provided)],
    case get_header_val("accept") of
	undefined ->
	    wrcall({set_metadata, 'content-type', hd(PTypes)}),
	    d(v3d4);
	_ ->
	    d(v3c4)
    end;

states.clj

  (defstate b4
    :test s/valid-entity-length?
    :yes :b3
    :no (stop-response 413))

  (defstate b3
    :body (fn [{:keys [handler request] :as args}]
            (if (= :options (:requestmethod request))
              (let [options-headers (or (s/options handler request) {})]
                {:status 200
                 :body ""
                 :headers options-headers})
              (c3 args))))

  (defstate c3
    :test (fn [handler request]
            (if-let [acceptv ((:headers request) "accept")]
              )))