code: public static boolean isValid(
          String variant,
          int yearOfEra,
          int month,
          int dayOfMonth
      ) {
  
          EraYearMonthDaySystem<HijriCalendar> calsys = CALSYS.get(variant);
          return ((calsys != null) && calsys.isValid(HijriEra.ANNO_HEGIRAE, yearOfEra, month, dayOfMonth));
  
      }
docs: /*[deutsch]
  <p>Pr&uuml;ft, ob die angegebenen Parameter ein wohldefiniertes Kalenderdatum beschreiben. </p>
  
  @param   variant     the variant of the underlying calendar system
  @param   yearOfEra   the year of era to be checked
  @param   month       the month to be checked
  @param   dayOfMonth  the day of month to be checked
  @return  {@code true} if valid else  {@code false}
  @see     #of(String, int, int, int)
  @since   3.34/4.29