How to add leading zeroes in xslt mapping

Hello All,

We have a requirement of  adding leading zeroes to a number in xslt mapping.

We tried like this but it's not working

<ns0:when test="$kunnr-length &gt;0">

<ns0:value-of-select="substring(../../KUNNR,1,4)"/>

<ns0:value-of-select="formatnumber(12345678,'00000000')"/>

Any ideas how to do this.

Thanks,

Sateesh