Lösung: Overloaded Templates
<xsl:template match="cd">
<tr style="background: lightgrey">
<td><xsl:value-of
select="titel"/></td>
</tr>
</xsl:template>
<xsl:template match="cd[preis]">
<tr style="background: orange">
<td>
<xsl:value-of select="titel"/>
<input type="button"
value="bestellen"/>
</td>
</tr>
</xsl:template>