tablecolumns.extension

Hi ,

  I discover today that I cannot use libxml2 anymore because
tablecolumns.extension is not supported for this XSL engine.

  I am reading the documentation for the option at:

http://docbook.sourceforge.net/release/xsl/current/doc/fo/tablecolumns.extension.html

  I do not really understand what this refer to ? Does anyone knows
what this extension is supposed to do (it is on by default).

Thanks !
-- 
Mathieu