    # File lib/active_support/vendor/xml-simple-1.0.11/xmlsimple.rb, line 128
      def initialize(defaults = nil)
        unless defaults.nil? || defaults.instance_of?(Hash)
          raise ArgumentError, "Options have to be a Hash."
        end
        @default_options = normalize_option_names(defaults, (KNOWN_OPTIONS['in'] + KNOWN_OPTIONS['out']).uniq)
        @options = Hash.new
        @_var_values = nil
      end