trying to reproduce fosi counters in xsl-fo

I can not find any information on how to create a counter in xsl-fo.  For example, I want to assign a label to each section in the document with an incremental value (XX 00) using a variable, but if an attribute is set on the section (insertchg), then I only want to increment the "00" portion of "XX 00".  If I use fo:number, I can't maintain the original value when a change occurs (because its counting the sections).  Any help would be appreciated.

L. Lentz