code: def is_subdomain_missing_zonefiles_record(rec):
      
      if rec['name'] != SUBDOMAIN_TXT_RR_MISSING:
          return False
  
      txt_entry = rec['txt']
      if isinstance(txt_entry, list):
          return False
  
      missing = txt_entry.split(',')
      try:
          for m in missing:
              m = int(m)
      except ValueError:
          return False
  
      return True
docs: Does a given parsed zone file TXT record encode a missing-zonefile vector?
      Return True if so
      Return False if not