docs: public static PeriodType millis() {
          PeriodType type = cMillis;
          if (type == null) {
              type = new PeriodType(
                  "Millis",
                  new DurationFieldType[] { DurationFieldType.millis() },
                  new int[] { -1, -1, -1, -1, -1, -1, -1, 0, }
              );
              cMillis = type;
          }
          return type;
      }