code: public void validate(VTimeZone target) throws ValidationException {
          for (final Observance observance : target.getObservances()) {
              Arrays.asList(DTSTART, TZOFFSETFROM, TZOFFSETTO).forEach(
                      property -> PropertyValidator.getInstance().assertOne(property, observance.getProperties()));
  
              PropertyValidator.getInstance().assertOneOrLess(TZNAME, observance.getProperties());
          }
      }
docs: {@inheritDoc}