For Python 2.2.1 or the CVS head, as of this posting, 
with Python configured for 4-byte unicode
(--enable-unicode=ucs4)
searches against unicode regular expressions that use 
characters above \xff don't seem to work.

Here's an example:

  invalid_xml_char = re.compile(u'[\ud800-\udfff]')
  invalid_xml_char.search(u'\ud800')

returns None, rather than a match.