docs: public static PeriodType yearMonthDay() {
          PeriodType type = cYMD;
          if (type == null) {
              type = new PeriodType(
                  "YearMonthDay",
                  new DurationFieldType[] {
                      DurationFieldType.years(), DurationFieldType.months(),
                      DurationFieldType.days(),
                  },
                  new int[] { 0, 1, -1, 2, -1, -1, -1, -1, }
              );
              cYMD = type;
          }
          return type;
      }