std.datetime.date.DateTimeException if a non-positive value is given.
auto dt = DateTime(Date(2010, 1, 1), TimeOfDay(7, 30, 0)); dt.yearBC = 1; assert(dt == DateTime(Date(0, 1, 1), TimeOfDay(7, 30, 0))); dt.yearBC = 10; assert(dt == DateTime(Date(-9, 1, 1), TimeOfDay(7, 30, 0)));
Year B.C. of the Gregorian Calendar counting year 0 as 1 B.C.