Seeking Equality
http://www.xml.com/pub/a/2005/06/08/tr.html

DuCharme, Bob
XML.com
2005

Abstract:

XPath 1.0 (and hence your XSLT style sheets) considers two elements to be equal if their string values are the same. The string value is essentially all of the PCDATA between the element's start and end tags, even if the element has descendant elements. For example, an XSLT processor considers the w and z elements in the following to be equal, because they both have a string value of "abcdefghi".