appendig to multiple output files

Is there a way to append output data for multiple output files using the
XSLT 1.1 approach with <xsl:document> ?

I want to generate two separate files (method="text") in one transformation 
process and think I understand the suggested approach of XSLT 1.1 
"16.5 Multiple Output Documents", the processor I use is 'xsltproc'
compiled against libxml2 2.4.13 and libxslt 1.0.9.

But how do I append data to the "other" document in my various templates 
without overwriting the output file?

Michael
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