constraints

# File actionpack/lib/action_dispatch/routing/mapper.rb, line 331
          def constraints(options, path_params)
            constraints = {}
            required_defaults = []
            options.each_pair do |key, option|
              if Regexp === option
                constraints[key] = option
              else
                required_defaults << key unless path_params.include?(key)
              end
            end
            @conditions[:required_defaults] = required_defaults
            constraints
          end