code: def ids
        if parse_ids?
          return @ids if @ids
          id_list = parsed_response['eSearchResult']['IdList']
          if id_list
            id_content = id_list['Id']
            id_content = [id_content].flatten
            @ids = id_content.map(&:to_i)
          else
            @ids = []
          end
        end
      end
docs: For ESearch, add convenience method that parses ids and converts to array of integers.
   Only works if either no retern mode specified or if it is :xml.