slides.titlepage.subtitle.properties — Specifies properties for slides titlepage title
<xsl:attribute-set name="slides.titlepage.subtitle.properties">
<xsl:attribute name="text-align">center</xsl:attribute>
<xsl:attribute name="space-after">1em</xsl:attribute>
<xsl:attribute name="font-family">
<xsl:value-of select="$slide.title.font.family"></xsl:value-of>
</xsl:attribute>
</xsl:attribute-set>