docs: def generate_timestamp(fmt=None):
      """
      Generate a timestamp to mark when this file was last modified.
  
      :param str fmt: Special format instructions
      :return str: YYYY-MM-DD format, or specified format
      """
      if fmt:
          time = dt.datetime.now().strftime(fmt)
      else:
          time = dt.date.today()
      return str(time)