docs: def getDocNumber(xml):
      """
      Parse <doc_number> tag from `xml`.
  
      Args:
          xml (str): XML string returned from :func:`aleph.aleph.downloadRecords`
  
      Returns:
          str: Doc ID as string or "-1" if not found.
      """
      dom = dhtmlparser.parseString(xml)
  
      doc_number_tag = dom.find("doc_number")
  
      if not doc_number_tag:
          return "-1"
  
      return doc_number_tag[0].getContent().strip()