code: public ZonedDateTime parse() {
                  if (isSimpleNumber()) {
                      return ZonedDateTime.now(ZoneOffset.UTC).plusSeconds(Long.parseLong(getValue()));
                  } else {
                      return parse(RFC_1123_DATE_TIME);
                  }
              }
docs: Always returns {@link ZonedDateTime}
  
  @return the parsed header type