    # File lib/action_controller/mime_responds.rb, line 102
          def respond_to(*types, &block)
            raise ArgumentError, "respond_to takes either types or a block, never both" unless types.any? ^ block
            block ||= lambda { |responder| types.each { |type| responder.send(type) } }
            responder = Responder.new(self)
            block.call(responder)
            responder.respond
          end