The year to set this Date's year to.
std.datetime.date.DateTimeException if the new year is not a leap year and the resulting date would be on February 29th.
assert(Date(1999, 7, 6).year == 1999); assert(Date(2010, 10, 4).year == 2010); assert(Date(-7, 4, 5).year == -7);
Year of the Gregorian Calendar. Positive numbers are A.D. Non-positive are B.C.