true, if the specified day is a leap day; otherwise, false.
Leap years in the Japanese calendar correspond to the same leap years in the Gregorian calendar. A leap year in the Gregorian calendar is defined as a Gregorian year that is evenly divisible by four, except if it is divisible by 100. However, Gregorian years that are divisible by 400 are leap years. A common year has 365 days and a leap year has 366 days.
A leap day is a day that occurs only in a leap year. For example, the 29th day of Nigatsu (February) is the only leap day.