DITA-OT Customization: Numbered Headings in PDF output

numbered-headings-custom.xsl

<?xml version='1.0' encoding='UTF-8'?>
<xsl:stylesheet version="2.0" xmlns:fo="http://www.w3.org/1999/XSL/Format" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<!-- 
    Numbered Headings in PDF output per <http://tech.groups.yahoo.com/group/dita-users/message/26819>, 26827, 26828 & 26794
    Template created via DITA-OT PDF plug-in generator <http://dita-generator.appspot.com/pdf-plugin> by Jarno Elovirta -->

  <xsl:template match="*" mode="getTitle">
    <xsl:variable name="topic" select="ancestor-or-self::*[contains(@class, &apos; topic/topic &apos;)][1]" />
    <xsl:variable name="id" select="$topic/@id" />
    <xsl:variable name="mapTopics" select="key(&apos;map-id&apos;, $id)" />
    <fo:inline>
      <xsl:for-each select="$mapTopics[1]">
        <xsl:choose>
          <xsl:when test="parent::opentopic:map" />
          <xsl:when test="ancestor-or-self::*[contains(@class, &apos; bookmap/frontmatter &apos;) or                                               contains(@class, &apos; bookmap/backmatter &apos;)]" />
          <xsl:when test="ancestor-or-self::*[contains(@class, &apos; bookmap/appendix &apos;)]">
            <xsl:number count="*[contains(@class, &apos; map/topicref &apos;)]                                 [ancestor-or-self::*[contains(@class, &apos; bookmap/appendix &apos;)]]" format="A.1.1" level="multiple" />
          </xsl:when>
          <xsl:otherwise>
            <xsl:number count="*[contains(@class, &apos; map/topicref &apos;)]                                 [not(ancestor-or-self::*[contains(@class, &apos; bookmap/frontmatter &apos;)])]" format="1.1" level="multiple" />
          </xsl:otherwise>
        </xsl:choose>
      </xsl:for-each>
    </fo:inline>
    <xsl:text> </xsl:text>
    <xsl:apply-templates />
  </xsl:template>
</xsl:stylesheet>

I saw your post on the dita-users yahoo group and am trying to implement this code, so i can get numbered headings. Aside from adding this code to a custom file or the custom.xsl file (as the plugin generator does), what other customizations are required? I added the code to my /fo/xsl/custom.xsl file and got the following error when I attempted run my XEP transform:

[java] Error at xsl:when on line 13 column 62 of custom.xsl:
[java] XPST0081 XPath syntax error at char 21 on line 13 in {parent::opentopic:map}:
[java] Undeclared namespace prefix {opentopic}
[java] Failed to compile stylesheet. 1 error detected.

Do you know what and where I need to make a declaration?

TIA,
Qiana