This library supports full W3C XML Schema regular expressions inclusive
all Unicode character sets and blocks.  It is implemented by the
technique of derivations of regular expressions.  The W3C syntax is
extended to support not only union of regular sets, but also
intersection, set difference, exor.  Matching of subexpressions is also
supported.  The library can be used for constricting lightweight
scanners and tokenizers.  It is a standalone library, no external regex
libraries are used.

WWW: http://www.haskell.org/haskellwiki/Regular_expressions_for_XML_Schema