Embedding javascript with xsl for converting xml to pd

I am trying to use Javascript with xsl. I have done
this before but for displaying something in the
browser. 
This time I am trying to conver xml file into a PDF
using FOP. So wondering if anyone has used javascript
embedded in xsl to create pdf files. I tried but it
gave me the following error

[ERROR] java.lang.NoSuchMethodException: For extension
function, could not find method
org.apache.xpath.objects.XNodeSet.getlength([ExpressionContext,]
).

I want to do some string manipulations which cannot
all be done using xsl string functions.
If anyone has done this before then could please
provide me a snippet.
Any help is appreciated.
Thanks,
Abhi


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