> Can anyone please tell me how to test whether a variable has been defined?

There is no such test. Variables in XSLT have scope based on their
appearance in the stylesheet not on runtime behaviour, so there would
be no point to such a test, you always know whetehr the variable is
defined or not.

> And also can you assgin a string to a variable using xsl:variable?
Yes, and XPath type. 

select="'string'"

David

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