[XQuery] limitations

[Michalmas]

Hi gents,

I was wondering what are the limitations of XQuery? For instance,
there are some limitations of regular exp (you can't parse what is not
defined by a regular language). Since XQuery uses XPath which uses reg
exp - does it bring any limitations to XQuery search engine?

I tried to google some examples, but mostly someone was able to
prepare interesting query.

I mean here typical XQuery and reg exp (there are some extensions to
reg exp that diminish such limitations somehow, but here i am
interested in pure definitions)

Thanks,
Michal