appending output to file using saxon

I want to cut a document into many smaller file fragments using XSL.  For this 
I use Saxon and <saxon:output>.

At the same time/during the same pass I want to create another file which
contains in XML form the ancestors for each block element (Sort of an
associative map that allows to navigate a dhtml Table of Contents later on).

While the first task is not a problem as I open and close a new document for
each fragment, the second task seems to be trickier.  I actually want to keep
this file open and append content to it.

I guess (haven't actually tested it, but it seems natural), that <saxon:output> 
creates a new file, or opens an existing file, but erases any content.

Is there a way to append content to an existing file using Saxon?  Or any other 
way?

Thank you,
---------
Jakob Fix.

PS: please CC me, I am on digest.

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