EXSLT, how to use its functions

Hello all, 
I need to use the node-set function of the EXSLT extention, I'm currently testing my 
stylesheets with XMLSpy 5 and it seems it doesn't support EXSLT. I downloaded the 
package exslt.zip from the EXSLT site
http://exslt.org/exsl/exsl.html
but I still have the node-set.xsl stylesheet missing (and many more) and it is not 
provided with the package, what can I do in order to use these extension functions?,
tia, 
lizet

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