Returns the full name of the day of the week of a date. If no argument is given, then the current local date/time, as returned by date:date-time is used as the default argument. The result is an English day name: one of 'Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday' or 'Friday'.
day-name($date-time as string?) ➔ string
The input date/time