Returns the day of the week given in a date 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. The numbering of days of the week starts at 1 for Sunday, 2 for Monday and so on up to 7 for Saturday.
day-in-week($date-time as string?) ➔ number
The input date/time