code: public static CalendarQuarter from(GregorianDate date) {
  
          PlainDate iso = PlainDate.from(date); // includes validation
          return CalendarQuarter.of(iso.getYear(), iso.get(PlainDate.QUARTER_OF_YEAR));
  
      }
docs: /*[deutsch]
  <p>Konvertiert das angegebene gregorianische Datum zu einem Kalenderquartal. </p>
  
  @param   date    gregorian calendar date (for example {@code PlainDate}
  @return  CalendarQuarter
  @throws  IllegalArgumentException if given date is invalid
  @since   3.28/4.24