[xsl] Problem with passing argument to external registered function

[Jesper Noehr <jesper@xxxxxxxxx>]

List,

I'm experiencing a problem, and I'm hoping someone might shed some
light on a solution.

Setup: Using gnome libxslt via python bindings.

I'm trying to pass data to an externally registered function. For
example, this function returns the uppercase version of what was
passed to it.

This works:
<xsl:value-of select="foo:bar('test')"/>

This doesn't:
<xsl:value-of select="foo:bar(element/.)"/>

Is it not possible to give XPath expressions as argument? I've tried
storing the content in both a param and a variable before sending it
on to the function. E.g.
<xsl:variable name="foo">
  This is a string.
</xsl:variable>
<xsl:value-of select="foo:bar($foo)"/>

...which also fails. The error I'm getting from libxslt is:
xmlXPathCompiledEval: evaluation failed
runtime error: file xsl/function.xsl element value-of
xsltValueOf: text copy failed

What am I doing wrong? Am I trying to go beyond the capabilities of
XSLT?

--
Jesper Nxhr, Information Systems Developer, Opera Software
tel: +47-24164348 / cell: +47-93460263 / jespern@xxxxxxxxx