In the last times I have been hacking in eXist-db, and writing XQuery. I noticed a website with a lot of interesting functions with the functx prefix. The eXist-db website help reference returns hits for this module. But it is not installed by default (or at least, it can happen on not being installed by default).
To install it, just run this XQuery command:
After installation the functx module can be loaded with
import module namespace functx = "http://www.functx.com" at "/db/system/repo/functx-1.0/functx/functx.xql";
Also, for reference, I found the list of eXist packages here.