@ISOWEEK — returns the ISO 8601 week number (1 through 53) for the specified date. The date may be in any input date format supported by this plugin, and it must be a valid date within the supported range.

Syntax:
%@ISOWEEK[date,infmt]

datethe date to examine; if omitted, uses today’s date
infmtthe input date format, used to interpret ambiguous dates

This function can also be used to find the number of ISO weeks in a given year by passing December 28 as the date:

echo There are %@isoweek[%_year-12-28] ISO weeks in %_year.

• Note: This function does not exist in 4NT / Take Command v10 and earlier.