Addition to BibReferences
Oleg Kiselyov, On parent pointers in SXML trees, Version is 1.1 Feb 12, 2003, 
http://okmij.org/ftp/Scheme/xml.html#parent-ptr. Discussion: 1, 2, 3, 4, 5.
Dan Olteanu, Holger Meuss, Tim Furche, Fran_E7_ois Bry, XPath: Looking Forward