Binding a variable within a "value-of select"

Hello,


Following problem:

I have a variable called "addorDef". All I need now is to use the value
of this variable within a path for another xsl:value-of.

<xsl:value-of select="WBSLServiceData/$addorDef/PostCode"/>

So a variabel within a variable.

I was thinking to use the { } as a solution.

<xsl:value-of select="WBSLServiceData/{$addorDef}/PostCode"/>
or
<xsl:value-of select="{WBSLServiceData/$addorDef/PostCode}"/>

But none of them works...

What am I missing?

Many Thanks,
Houman