In some date calculations, adding months or years can cause the date to fall on a day of the month which is not valid (e.g. February 29th 2001 or June 31st 2000). If overflow is allowed (as is the default), then the month will be incremented accordingly (so, February 29th 2001 would become March 1st 2001, and June 31st 2000 would become July 1st 2000). If overflow is not allowed, then the day will be adjusted to the last valid day in that month (so, February 29th 2001 would become February 28th 2001 and June 31st 2000 would become June 30th 2000).
alias AllowDayOverflow = Flag!("allowDayOverflow");
AllowDayOverflow only applies to calculations involving months or years.
If set to
AllowDayOverflow, then day overflow is not allowed.
Otherwise, if set to
AllowDayOverflow, then day overflow is