xsl:sort does not work when select="some expression"

["Roytman, Alex" <ro...@peacetech.com>]

Hello,

I was trying to find in xsl specs whether it allowed to use expression in
SORT clause but could not find any info. since the syntax is <xsl:sort
select="..."/> has *select* I assume it is an expression and should be
evaluated before executing sort.

However

<xsl:sort select="$sortcol"/>

does not work, while

<xsl:sort select="stitle"/> works just fine


Thank you in advance

Alex