>> In XSLT 1.0 you have 4 datatypes: number, boolean, string and nodeset.
>
>actually there is another, and that is the type that will be returned in
>this case (with an xsl:variable with eleemnt content). 
>result tree fragment.
>

Well, yes.  Forgot about that in 1.0 but how would the OP test for a result
tree fragment
for the purposes of signifying "nil" or "null" without incurring a runtime
error, given that the operations
permitted on a result tree fragment are a subset of those permitted on a
node-set?

Justin Johansson

*** A horse with no name is called Lambda ***