code: public static CronConstraint ensureEitherDayOfYearOrMonth() {
          return new CronConstraint("Both, a day-of-year AND a day-of-month or day-of-week, are not supported.") {
              private static final long serialVersionUID = 520379111876897579L;
  
              @Override
              public boolean validate(Cron cron) {
                  CronField dayOfYearField = cron.retrieve(CronFieldName.DAY_OF_YEAR);
                  if (dayOfYearField != null && !(dayOfYearField.getExpression() instanceof QuestionMark)) {
                      return cron.retrieve(CronFieldName.DAY_OF_WEEK).getExpression() instanceof QuestionMark
                              && cron.retrieve(CronFieldName.DAY_OF_MONTH).getExpression() instanceof QuestionMark;
                  }
  
                  return true;
              }
          };
      }
docs: Creates CronConstraint to ensure that either day-of-year or month is assigned a specific value.
  
  @return newly created CronConstraint instance, never {@code null};