FO: gap between cells in a table

  Hi

  I have to design a table in XSL FO, and the client would like
to have the overall layout like in the following image:

    http://www.fgeorges.org/tmp/table-headers.png

  My question is about the gap between some of those cells (in
this image between "sub-tables" A, B, C and D, and the cell "Type
of activity".)  While in the "sub-tables" the borders should be
collapsed.

  What is the best approach for this problem?

  I thought to use a table with a gap between its cells and
without borders collapsing, its cells being sub-tabels which have
border-collapse="collapse".  Do you think it is a good idea?  Is
there something easier?  What is the easiest way to set the gap
width between the sub-tables?

  Thank you, best regards,

-- 
Florent Georges
http://www.fgeorges.org/