MicroXML is a delightful tiny subset of XML, removing everything
  that makes XML a nightmare to deal with in practice.
  nxml-uxml-mode is a major mode for Emacs that slightly modifies
  the XML parser of nxml-mode to forbid most (though, at present,
  not quite all) constructs which are allowed in XML 1.0 but
  disallowed in MicroXML.