constraints

# File actionpack/lib/action_dispatch/routing/mapper.rb, line 369
          def constraints(options, path_params)
            options.group_by do |key, option|
              if Regexp === option
                :constraints
              else
                if path_params.include?(key)
                  :path_params
                else
                  :required_defaults
                end
              end
            end
          end