note 8141 added to Date and Time functions

Please note that the calendar week algorithm to apply is country-specific. The first week of a year is usually just a partial week (e.g. Wed-Sun), and the ideas whether this partial week is week 0, week 52 of the previous year, or week 1 depend on social (and business) conventions which can vary across countries; sometimes the definition varies according to whether that partial week has at least 4 days. These conventions may even vary with time; for example, Germany had its weeks from Sunday to Saturday and went to a Monday-to-Sunday cycle some time between ten and twenty years ago. http://www.php.net/manual/ref.datetime.php