[xsl] sum() over attributes is 0

[Andreas Kemkes <a5sk4s@xxxxxxxxx>]

I'm not having much success using the sum() function over a node set.

The
following two expressions

<xsl:comment>
  <xsl:text>sum: </xsl:text>
<xsl:value-of select="sum(//lc:container[lc:item]/@select)"/>
</xsl:comment>
<xsl:comment>
  <xsl:text>list of select attributes: </xsl:text>
<xsl:for-each select="//lc:container[lc:item]">
    <xsl:value-of
select="@select"/>
    <xsl:text> </xsl:text>
  </xsl:for-each>
</xsl:comment>
result in the following output:

    <!--sum: 0-->
    <!--list of select
attributes: 2 3 1 -->

I'm not clear why the result of sum() is 0.  Are there
any other prerequisites that I'm missing?

Thanks again.
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