RE: [xsl] Possible to pass 'empty sequence' to function?

> if you don't use as then an xsl:variable with content and no
> select attribute produces a temporary tree, what we used to
> lovingly call a result tree fragment.
>
> <xsl:variable name="x">hello</xsl:variable>
>
> $x is (a sequence of one) document node that has a single
> text node child that has string value "hello"
>
>
> <xsl:variable name="y" as="string?">hello</xsl:variable>
>
> $x is (a sequence of one) string with value "hello"


Is this really the case?  Does it really mean that the processor doesn't
construct the temporary tree (and then atomise it?) - if so then it's
really useful.