Metadata Munging with XQuery (and freelib-marc4j-exist) by Kevin S. Clarke.
I searched and didn’t find a video to go along with these slides. If you know of one, please ping me.
Slides 5 through 20 are all XQueries that you can run with a XQuery 3.1 processor.
Slide 21 is a list of suggested resources on XQuery.
I would add Saxon to any list of XQuery tools. There is a commercial and home (free) version of Saxon.
Suffice it to say that Michael Kay, the primary author of Saxon, has played a major role in XSLT, XPath and XQuery for a number of years.
Nothing against other products but Saxon is the baseline against which XSLT, XPath and XQuery feature sets are measured.