docs: public DateTime toDateTimeAtStartOfDay(DateTimeZone zone) {
          zone = DateTimeUtils.getZone(zone);
          Chronology chrono = getChronology().withZone(zone);
          long localMillis = getLocalMillis() + 6L * DateTimeConstants.MILLIS_PER_HOUR;
          long instant = zone.convertLocalToUTC(localMillis, false);
          instant = chrono.dayOfMonth().roundFloor(instant);
          return new DateTime(instant, chrono).withEarlierOffsetAtOverlap();
      }