Returns the week of the year as a number. If no argument is given, then the current local date/time, as returned by date:date-time is used as the default argument.
week-in-year($date-time as string?) ➔ number
The input date/time
Links to specifications
For the purposes of numbering, counting follows ISO 8601: week 1 in a year is the week containing the first Thursday of the year, with new weeks beginning on a Monday.