constraints

# File actionpack/lib/action_dispatch/routing/mapper.rb, line 267
          def constraints
            @constraints ||= {}.tap do |constraints|
              constraints.merge!(scope[:constraints]) if scope[:constraints]

              options.except(*IGNORE_OPTIONS).each do |key, option|
                constraints[key] = option if Regexp === option
              end

              constraints.merge!(options[:constraints]) if options[:constraints].is_a?(Hash)
            end
          end