formats

# File actionpack/lib/action_dispatch/http/mime_negotiation.rb, line 56
      def formats
        @env["action_dispatch.request.formats"] ||= begin
          params_readable = begin
                              parameters[:format]
                            rescue ActionController::BadRequest
                              false
                            end

          if params_readable
            Array(Mime[parameters[:format]])
          elsif use_accept_header && valid_accept_header
            accepts
          elsif xhr?
            [Mime::JS]
          else
            [Mime::HTML]
          end
        end
      end