How to generate an Identifer in XQuery

I'm looking for a solution to generate an identifier in a XQuery query. But
it seems that we cannot use XSLT functions in XQuery ( generate-id() ). Then
another solution would have to generate a ID with XQuery, for example by
using the Relations between the nodes: Parent, Children, Siblings,
Ancestors, Descendants; kind of : "count (preceding:: noeudx) +1" , but I
don't know how to write it properly.
I specify that the identifiers I want to generate should be affected in a variable so that I can use them in the query.

Thanks for help !!