A row group is a <tbody>. The idea is therefore to have a border-bottom on
<td> elements in the last <tr> in each <tbody>. I tried this:

  <!-- Table cell -->
  <xsl:template match="td">
    <fo:table-cell>
      <xsl:if test="parent::tr[position()=last()]">

        <xsl:attribute name="border-bottom">0.5pt solid black</xsl:attribute>
      </xsl:if>
      <fo:block><xsl:apply-templates/></fo:block>
    </fo:table-cell>
  </xsl:template>

The result is that I get border-bottom on every row, and I don't understand
why.

Gustaf