boolean() Function  
Converts its argument to a boolean value.
 
Inputs

An object. The object is converted to a boolean value. This conversion is described in the following subsection.

 
Output

The boolean value corresponding to the input object. Objects are converted to boolean values as follows:

    A number is true if and only if it is not zero, negative zero, or NaN (not a number).

    A node-set is true if and only if it is not empty.

    A string is true if and only if its length is greater than zero.

    All other datatypes are converted in a way specific to those datatypes.
 
Defined in

XPath section 4.3, Boolean Functions.
 
Example

The following example demonstrates the results of invoking the boolean() function against a variety of argument types. Here's our XML document:

<?xml version="1.0"?>
<test>
<p>This is a test XML document used by several 
of our sample stylesheets.</p>
<question>
<text>When completed, the Eiffel Tower was the 
tallest building in the world.</text>
<true>Yes!  The Eiffel Tower was the world's 
tallest building until 1932, when
New York's Empire State Building opened. </true>
<false>No, the Eiffel Tower was the world's tallest 
building for over 30 years.</false>
</question>
</test>

We'll process this document with the following stylesheet:

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

  <xsl:output method="text"/>

  <xsl:variable name="newline">
<xsl:text>
</xsl:text>
  </xsl:variable>

  <xsl:template match="/">
    <xsl:value-of select="$newline"/>
    <xsl:text>Tests of the boolean() function:</xsl:text>

    <xsl:value-of select="$newline"/>
    <xsl:value-of select="$newline"/>
    <xsl:choose>
      <xsl:when test="boolean(true())">
        <xsl:text>   "boolean(true())"   returned true!</xsl:text>
      </xsl:when>
      <xsl:otherwise>
        <xsl:text>   "boolean(true())"   returned false!</xsl:text>
      </xsl:otherwise>
    </xsl:choose>

    <xsl:value-of select="$newline"/>
    <xsl:choose>
      <xsl:when test="boolean(true)">

        <xsl:text>   "boolean(true)"     returned true!</xsl:text>
      </xsl:when>
      <xsl:otherwise>
        <xsl:text>   "boolean(true)"     returned false!</xsl:text>
      </xsl:otherwise>
    </xsl:choose>

    <xsl:value-of select="$newline"/>
    <xsl:choose>
      <xsl:when test="boolean('false')">
        <xsl:text>   "boolean('false')"  returned true!</xsl:text>
      </xsl:when>
      <xsl:otherwise>
        <xsl:text>   "boolean('false')"  returned false!</xsl:text>
      </xsl:otherwise>
    </xsl:choose>

    <xsl:value-of select="$newline"/>
    <xsl:choose>
      <xsl:when test="boolean('7')">
        <xsl:text>   "boolean('7')"      returned true!</xsl:text>
      </xsl:when>
      <xsl:otherwise>
        <xsl:text>   "boolean('7')"      returned false!</xsl:text>
      </xsl:otherwise>
    </xsl:choose>

    <xsl:value-of select="$newline"/>
    <xsl:choose>
      <xsl:when test="boolean(/true)">
        <xsl:text>   "boolean(/true)"    returned true!</xsl:text>
      </xsl:when>
      <xsl:otherwise>
        <xsl:text>   "boolean(/true)"    returned false!</xsl:text>
      </xsl:otherwise>
    </xsl:choose>

    <xsl:value-of select="$newline"/>
    <xsl:choose>
      <xsl:when test="boolean(//true)">
        <xsl:text>   "boolean(//true)"   returned true!</xsl:text>
      </xsl:when>
      <xsl:otherwise>
        <xsl:text>   "boolean(//true)"   returned false!</xsl:text>
      </xsl:otherwise>
    </xsl:choose>
  </xsl:template>

</xsl:stylesheet>

Here are the results:


Tests of the boolean() function:

   "boolean(true())"   returned true!
   "boolean(true)"     returned false!
   "boolean('false')"  returned true!
   "boolean('7')"      returned true!
   "boolean(/true)"    returned false!
   "boolean(//true)"   returned true!

See Section 4.2.1.2 in Chapter 4 for more examples and information.