If only there was one good library. libxml2 is the leading one, and it has been beleaguered by problems internal and external. It has had ABI instability and been besieged by CVE reports.

I agree it shouldn’t be hard. On the evidence, though, it is. I suspect the root problem is lack of tools. Lex and yacc tools for Unicode are relatively scarce. At least that’s what’s set me back from rolling my own.