best way to divide selected elements?

I currently have an xsl that takes a directory file list, then based on tags
within each file, contructs an xml file in which the file names are grouped
by category, like this:

<category>
	<file>file_x.html</file>
	<file>file_x.html</file>
	....
	<file>file_x.html</file>
	<file>file_x.html</file>
</category>

I'd like to change it so that if category element is going to include more
than 20 file elements another category element is created:

<category>
	<file>file_x.html</file>
	... 19 more times
</category>

<category>
	<file>file_x.html</file>
	... 5 more times, for example
</category>

Any advice on the best way to do this?

______________________________________________________

Marc Elliott, HNW Digital, Inc.
Digital Solutions for High-Net-Worth Marketers



 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list