There is always the good old trick of adding print statements around in the code, which is xslt translates to <xsl:message>
. Here is a snippet from my frontmatter transformation:
<!--
<xsl:message>createFrontMatter_1.0</xsl:message>
<xsl:message>artworkPrefix=<xsl:copy-of select="$artworkPrefix"/></xsl:message>
<xsl:message>customizationDir.url=<xsl:value-of select="$customizationDir.url"/></xsl:message>
<xsl:message>imageLogoPath=<xsl:value-of select="$imageLogoPath"/></xsl:message>
<xsl:message>imageNotePath=<xsl:value-of select="$imageNotePath"/></xsl:message>
<xsl:message>imageWatermarkPath=<xsl:value-of select="$imageWatermarkPath"/></xsl:message>
<xsl:message>page-width=<xsl:value-of select="$page-width"/></xsl:message>
<xsl:message>page-height=<xsl:value-of select="$page-height"/></xsl:message>
-->
If I uncomment this, I get a nice debugging block of text in the output log, showing the various values for the settings I use.