concerns

# File actionpack/lib/action_dispatch/routing/mapper.rb, line 2025
        def concerns(*args)
          options = args.extract_options!
          args.flatten.each do |name|
            if concern = @concerns[name]
              concern.call(self, options)
            else
              raise ArgumentError, "No concern named #{name} was found!"
            end
          end
        end