<xsl:when test="number('12')=number('12')">
is true, because the string '12' casts to a number.

<xsl:when test="number('xy')=number('xy')">
is false as the string 'xy' casts to the special value NaN which is not 
equal to anything, even itself.


Thanks David, learned something today, which I never tried earlier. Though 
I still need to test it.
Hope it works in 1.0. :-)
cheers
Pankaj