This presentation: http://www.ibiblio.org/xml/slides/xmlonesanjose2001/xinclude
XML Base Specification: http://www.w3.org/TR/xmlbase
XInclude Specification: http://www.w3.org/TR/xinclude
XPath Specification: http://www.w3.org/TR/xpath
XPointer Specification: http://www.w3.org/TR/xptr
XML Bible, Gold edition
Elliotte Rusty Harold
Hungry Minds, 2001
ISBN 0-7645-4819-0