A positive integer from 1 through 13 that indicates the leap month in the specified year and era.
-or-
Zero if this calendar does not support a leap month, or if the year and era parameters do not specify a leap year.
In a calendar that supports a leap month, the leap month can occur either after a particular month or after any month in a year. For example, the EastAsianLunisolarCalendar.GetMonth(DateTime) method returns a number from 1 through 13 that indicates the month associated with a specified date. If there is a leap month between the eighth and ninth months of the year, the EastAsianLunisolarCalendar.GetMonth(DateTime) method returns 8 for the eighth month, 9 for the leap eighth month, and 10 for the ninth month.