docs: def append_vobject(self, ical, filename=None):
          """Append a Remind command generated from the iCalendar to the file"""
          if not filename:
              filename = self._filename
          elif filename not in self._reminders:
              return
  
          with self._lock:
              outdat = self.to_reminders(ical)
              open(filename, 'a').write(outdat)
  
          return Remind._get_uid(outdat)