method_missing

# File actionpack/lib/abstract_controller/collector.rb, line 25
    def method_missing(symbol, &block)
      const_name = symbol.upcase

      unless Mime.const_defined?(const_name)
        raise NoMethodError, "To respond to a custom format, register it as a MIME type first: "            "http://guides.rubyonrails.org/action_controller_overview.html#restful-downloads. "            "If you meant to respond to a variant like :tablet or :phone, not a custom format, "            "be sure to nest your variant response within a format response: "            "format.html { |html| html.tablet { ... } }"
      end

      mime_constant = Mime.const_get(const_name)

      if Mime::SET.include?(mime_constant)
        AbstractController::Collector.generate_method_for_mime(mime_constant)
        send(symbol, &block)
      else
        super
      end
    end