Invalid Usage of Element

Just ran into something annoying the past 10 minutes when working on a BPEL process (related to XSLT).

My transformation included the following (which I had manually entered in JDeveloper):

<ns0:QualificationDate> <xsl:if test="number(ns1:Highest/ns1:QualificationDate) > 0"> <xsl:value-of select="number(ns1:Highest/ns1:QualificationDate) + 190000"/> </xsl:if> </ns0:QualificationDate>

However, when I clicked on the "Design" tab of the mapper tool to switch from Source to Design mode, I received the following error:

Transformation_2.xsl
Error: Invalid Usage of <if> Element

Turns out, the correct usage of the <if> element is the following:

<xsl:if test="number(ns1:Highest/ns1:QualificationDate) > 0">
 <ns0:QualificationDate>
   <xsl:value-of select="number(ns1:Highest/ns1:QualificationDate) + 190000"/>
 </ns0:QualificationDate>
</xsl:if>

It's the little things that get you sometimes.