def data=(data)
      raise ArgumentError, 'No document data specified' if data.nil?

      @data = Nokogiri::XML.parse(data.to_s)
    end
def data=(data)
      raise ArgumentError, 'No document data specified' if data.nil?

      @data = Nokogiri::XML.parse(data.to_s)
    end
Sets the raw XML data for the {Document}.

 @param [String] data A string representing the document.
 @raise [ArgumentError] Raised if the specified data was nil.