Workaholic | 🤸🏻 | Learning library

The function fn:sort(...) exists in three versions, with up to three arguments:

1. $input as item()*: the input sequence,
2. $collation as xs:string?: the collation for string comparison (or an empty sequence),
3. $key as function(item()) as xs:anyAtomicType*) as item()*: a function item that extracts the sort key (i.e. the part that should be compared) from the items to sort.

Since you don't want to sort strings, the second argument should be ().

The sort key in your case is the starting date and time of each appointment. So you need to supply a function item that, given an Appointment node, returns the xs:dateTime of its start date: function($app) { fn:dateTime($app/Start/@date, $app/Start/@time) }

Putting everything together: