I read Bob's chapter on indexes, particularly the bottom of page 321 (Fourth Ed). There is an XEP extension to mark the page numbers in bold for preferred indexterms. If I understand correctly, this doesn't work for Antenna House Formatter (my chosen processor) or FOP (at least it didn't for me).
So I customized the template that I think is responsible for putting out the page numbers: <xsl:template match="indexterm" mode="reference"> ... <!-- begin customization --> <xsl:choose> <xsl:when test="@significance='preferred'"> <fo:basic-link internal-destination="{$id}" xsl:use-attribute-sets="index.preferred.page.properties"> <fo:page-number-citation ref-id="{$id}"/> </fo:basic-link> </xsl:when> <xsl:otherwise> <fo:basic-link internal-destination="{$id}" xsl:use-attribute-sets="index.page.number.properties"> <fo:page-number-citation ref-id="{$id}"/> </fo:basic-link> </xsl:otherwise> </xsl:choose> <!-- end customization --> ... What I have does the expected thing using fop or ahf, and is apparently ignored by xep. With all three processors, I get bold page numbers for preferred indexterms. What I'm not sure about is whether this is the only template that needs changing. It works for all the indexterms in my test book. Bob, I can send you a file if you'd like to include it in the distribution at some point. It is a small change that adds functionality.