- strftime: documentation ( source)
- date: documentation ( source)
- strtotime: documentation ( source)
- gmdate: documentation ( source)
<?php
echo strftime("%Y %W", strtotime("-1 week", strtotime("2013W01"))) . "\n";
echo strftime("%Y %W", strtotime("+1 week", strtotime("2012W52"))) . "\n";
echo gmdate("Y W", strtotime("2012W53")) . "\n";
echo strftime("%Y %W", strtotime("2012W53")) . "\n";
echo date("Y W", strtotime("2012W53")) . "\n";
?>