Sorting alpha numeric values

I have a data set:
<Root>
<Elem val = "A1"/>
<Elem val = "A2"/>
<Elem val = "A21"/>
<Elem val = "A3"/>
</Root>

And a template:

<xsl:template match="/">
  <xsl:for-each select="./Root/Elem">
    <xsl:sort select="@val"/>
    <xsl:value-of select="./@val"/>
  </xsl:for-each>
</xsl:template>

I was hoping to sort the Elems into
A1
A2
A3
A21

But I cannot get a hybrid alpha/numeric sort happening.  Is there some
setting I'm missing, or could someone suggest how I can do this.  The
ability to create a custom routine on which to compare the values would
be handy, although I suspect the performance could be an issue.

Thanks in Advance!!

Hugh Dixon


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