Testing for presence of alphabetical characters

Using Saxon 851... can someone tell me why the
following expression returns false?

<?xml version="1.0"?>
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<xsl:for-each select="//entry">
<xsl:variable name="cont" select="."/>
<xsl:variable name="alpha"
select="'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'"/>
<xsl:if test="contains($alpha, $cont)">
<!-- do something -->
</xsl:if>
</xsl:for-each>
</xsl:template>

<?xml version="1.0"?>
<document>
<entry>1a</entry>
</document>


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