IntervalCalendar class and example is based on the iCalendarGroup class, graciously contributed to YUI by John Peloquin, of W. Hardy Interactive, Inc..
The Calendar widget is commonly used to select pairs of dates, representing the start and end dates of an interval, for example flight departure and return dates, or hotel check-in and check-out dates.
This example defines a custom IntervalCalendar class, based on CalendarGroup, which is designed specifically for this use case.