append_features

# File lib/rss/syndication.rb, line 16
    def self.append_features(klass)
      super

      klass.install_must_call_validator(SY_PREFIX, SY_URI)
      klass.module_eval do
        [
          ["updatePeriod"],
          ["updateFrequency", :positive_integer]
        ].each do |name, type|
          install_text_element(name, SY_URI, "?",
                               "#{SY_PREFIX}_#{name}", type,
                               "#{SY_PREFIX}:#{name}")
        end

        %w(updateBase).each do |name|
          install_date_element(name, SY_URI, "?",
                               "#{SY_PREFIX}_#{name}", 'w3cdtf', name)
        end

        alias_method(:_sy_updatePeriod=, :sy_updatePeriod=)
        def sy_updatePeriod=(new_value)
          new_value = new_value.strip
          validate_sy_updatePeriod(new_value) if @do_validate
          self._sy_updatePeriod = new_value
        end
      end
    end