Returns a sequence number based on the latest Sunday of the year before or on the input date, unless there are no more Sundays that year.
This method generally returns the sequence number of the latest Sunday of the year before or on the input date value unless there are no more Sundays that year. The return values for dates near the beginning or end of the year are determined by various details.
Consider the year 2003. The first day of 2003 is a Wednesday. This means an input date of Saturday (day\month\year) 4\1\2003 returns 1, and Sunday 5\1\2003 returns 2.
The last day of 2003 is also a Wednesday. An input of Saturday 27\12\2003 returns 52, and Sunday 28\12\2003 returns 1 because there are no more Sundays that year.
The year 2013 starts on a Sunday. An input of 1\1\2013 returns a 1.