rest("/things")
.get("/").outType(Thing[].class)
.param().name("param1").type(RestParamType.query).required(FALSE)
  .description("param 1").endParam()

.responseMessage().code(200).message("Some things..")
  .header("number-of-things").dataType("integer").endHeader()
  .endResponseMessage()

.responseMessage().code(400)
  .message("Bad request.")
  .responseModel(Error.class).endResponseMessage()

400:
  description: "Bad request."
  schema:
    $ref: "#/definitions/Error"
  responseSchema:
    $ref: "#/definitions/Error"