def to_xml_string(str = '')
      return if empty?
      str << '<protectedRanges>'
      each { |range| range.to_xml_string(str) }
      str << '</protectedRanges>'
    end
def to_xml_string(str = '')
      return if empty?
      str << '<protectedRanges>'
      each { |range| range.to_xml_string(str) }
      str << '</protectedRanges>'
    end
Serializes the protected ranges
 @param [String] str
 @return [String]