A Normative References

RFC 2119
Scott Bradner, RFC 2119: Key words for use in RFCs to Indicate Requirement Levels. Internet Engineering Task Force, 1997.
XML
Tim Bray, Jean Paoli, C.M. Sperberg-McQueen, and Eve Maler, editors. Extensible Markup Language (XML) 1.0 (Second Edition). World Wide Web Consortium, 2000.
XPtrFrame
Paul Grosso, Eve Maler, Jonathan Marsh, and Norman Walsh, editors. XPointer Framework. World Wide Web Consortium, 2002.
XML-Names
Tim Bray, Dave Hollander, and Andrew Layman, editors. Namespaces in XML. World Wide Web Consortium, 1999.