RE: [ACTION 189] Split special requirements into several data categories

Hi Jirka, all,

> I think that regular expressions are good enough for this,
> but instead of reinventing our own subset I would prefer 
> to use syntax defined by XML Schema 1.0 or by XPath
> 2.0/XSLT 2.0 (which is slightly extended XML Schema syntax).

I think the idea is to have a very small subset of regex that is supported by all (or at least a very large number) of engines.

Note that very often the expression won't be directly used in a XPath/XSLT environment as the checks are done somewhere after the document is read, in validation tools written in Java, C#, etc.

Cheers,
-yves