# 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