How to use xsl:result-document to create HTML and XML output docs?

Hi,

How can I use xsl:result-document to split a single XML input stream into two 
separate output files, ie one HTML and one XML (or rather SVG)?

Have this working for HTML output files only.  When I try to generate the svg 
file, I get the following error ...
"The system identifier of the principal output file is unknown".  Using Saxon 
7.1

Have the following specified in the stylesheet.

<xsl:output method="html"/>
<xsl:output name="svg-format" method="xml"/>

<xsl:result-document href="test.html">...</xsl:result-document>
<xsl:result-document href="test.svg" 
format="svg-format">...</xsl:result-document>


Thanks,
Anita