Where is the DTD for XSL

When we write an xsl, we get some error if the XSL is not proper. How the
validation actually happens? Where is the DTD for XSL?
Can any one tell me the logic behind the process.
http://www.w3.org/TR/xslt#dtd"; This link has the DTD.
But in the namespace we use this <xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform";  version="1.0">




Thanks in Advance
-Sanghamitra



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