is there parameter to limit the depth of section numbering in the xsl stylesheets to a certain section level (using docbook-xsl-1.41, saxon 6.4.3, fop-0.19)?

To limit the section depth listed in the toc I included <xsl:param name="toc.section.depth" select="3"/> to my param.xsl customization stylesheet which has no affect at all? I'm not that familiar yet with xsl and the stylesheets - is there another attribute I could set?