Great to see that somebody else creates a true open source XSLT 3 and XPATH 3 implementation! I worked on projects which refused to use anything more modern than XSLT & XPATH 1.0 because of lack of support in the non Java/Net World (1.0 = tech from 1999). Kudos to Saxon though, it was and is great but I wished there were more implementations of XSLT 2.0 & XPATH 2.0 and beyond in the open source World... both are so m…
For some things that may just be down to how uses are specified. For YANG, the spec calls out XPath 1.0 as the form in which constrains (must and when statements) must be expressed.
So one is forced to learn and use XPath 1.0.