Use strings as arguments of boolean() function. : Boolean Functions  « XSLT stylesheet « XML Tutorial

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3. Boolean Functions

A string is true if and only if its length is non-zero. 


File: Data.xml
<?xml version="1.0" encoding="utf-8"?>
<data>
    <text>999</text>
    <text>A123</text>
    <text>-16</text>
    <text>0</text>
    <text/>
    <text>false</text>
</data>
File: Transform.xslt

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet
      version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

    <xsl:template match="/">
      <TABLE border="1">
        <TR>
          <td>text</TH>
          <td>boolean</TH>
        </TR>
        <xsl:for-each select="//text">
          <TR>
            <TD>
              <xsl:value-of select="."/>
              <xsl:text/>
            </TD>
            <TD>
              <xsl:value-of select="boolean(text())"/>
            </TD>
          </TR>
        </xsl:for-each>
      </TABLE>
    </xsl:template>
</xsl:stylesheet>

<?xml version="1.0" encoding="UTF-8"?><TABLE border="1"><TR>
<td>text</TH><td>boolean</TH></TR><TR><TD>999</TD><TD>true</TD>
</TR><TR><TD>A123</TD><TD>true</TD></TR><TR><TD>-16</TD><TD>true
</TD></TR><TR><TD>0</TD><TD>true</TD></TR><TR><TD/><TD>false</TD>
</TR><TR><TD>false</TD><TD>true</TD></TR></TABLE>