check_validity!

# File activemodel/lib/active_model/validations/format.rb, line 20
      def check_validity!
        unless options.include?(:with) ^ options.include?(:without)  # ^ == xor, or "exclusive or"
          raise ArgumentError, "Either :with or :without must be supplied (but not both)"
        end

        check_options_validity :with
        check_options_validity :without
      end