<xsl:when>

The XSLT <xsl:when> element provides a conditional test to use against the contents of an XML file within the scope a larger <xsl:choose> conditional evaluation.

<xsl:when> supports one attribute – test – which must return a Boolean value (true or false) through the application of a XPATH expression, or evaluation of a variable.

The <xsl:when> element cannot be used on its own; it must always be used together with the <xsl:choose> element. When used inside an <xsl:choose> then only the first <xsl:when> whose test evaluates to true will be processed.

If your intention is to evaluate a simple Boolean expression (and not a sequence of alternatives) and nothing else, then look into using the <xsl:if> element instead.

Syntax

<xsl:choose>
    <xsl:when test="expression_1">
        <!-- evaluated when expression_1 is true. -->
    </xsl:when>
    <xsl:when test="expression_2">
        <!-- evaluated when expression_2 is true. -->
    </xsl:when>
    <!-- ... -->
    <xsl:when test="expression_n">
        <!-- evaluated when expression_n is true. -->
    </xsl:when>
    <xsl:otherwise>
        <!-- evaluated when none of the preceding expressions are true.-->
    </xsl:otherwise>
</xsl:choose>

<xsl:choose> contains one or more nested <xsl:when> elements and one optional <xsl:otherwise> element. Only the contents one <xsl:when> element is evaluated when its corresponding expression returns true; otherwise the <xsl:otherwise> content is evaluated if defined.

   1:  

   2: <xsl:when select="expression">

   3:     <!-- Do something when evaluating to true. -->

   4: </xsl:when>

   5:  

   6:  

Attributes

Examples

The <xsl:when> element must be used inside a <xsl:choose> element. Refer to the examples presented under <xsl:choose> for a better overview on how to use this function in an XSLT transform.