Is replaced by either the 2-digit ISO week number or the
standard week number with leading zero, or a 4-alphanumeric character
text of the current week of year
(see Calendar option --starting-day=argument, Calendar option --iso-week-number=yes|no, and Aspects in Internationalization, for further details), e.g.:
The text ‘Today is %K of week %k’ will be expanded to
→ ‘Today is Monday of week 24’, in case the actual system date is the 10th June 1996.