code: public void setPeriod(long startInstant, long endInstant, Chronology chrono) {
          chrono = DateTimeUtils.getChronology(chrono);
          setValues(chrono.get(this, startInstant, endInstant));
      }
docs: Sets all the fields in one go from a millisecond interval.
  
  @param startInstant  interval start, in milliseconds
  @param endInstant  interval end, in milliseconds
  @param chrono  the chronology to use, null means ISO chronology
  @throws ArithmeticException if the set exceeds the capacity of the period