XSLT, 2nd Edition

Defining a Parameter in a Template

To define a parameter in a template, use the <xsl:param> element. Here’s an example of a template that defines two parameters:

<xsl:template name="calcuateArea">
  <xsl:param name="width"/>
  <xsl:param name="height"/>

  <xsl:value-of select="$width * $height"/>
</xsl:template>

Conceptually, this is a lot like writing code in a traditional programming language, isn’t it? Our template here defines two parameters, width and height, and outputs their product.

If you want, you can define a default value for a parameter. There are two ways to define a default value; the simplest is to use a select attribute on the <xsl:param> element:

<template name="addTableCell">
  <xsl:param name="bgColor" select="'blue'"/>
  <xsl:param name="width" select="150"/>
  <xsl:param name="content"/>
  <td width="{$width}" bgcolor="{$bgColor}">
    <xsl:apply-templates select="$content"/>
  </td>
</template>

In this example, the default values of the parameters bgColor and width are 'blue' and 150, respectively. If we invoke this template without specifying values for these parameters, the default values are used. Also notice that we generated the values of the width and bgcolor attributes of the HTML <td> tag with attribute value templates, the values in curly braces. For more information, see the section Attribute Value Templates” in Chapter 3.

One thing to note about this example is that the content parameter doesn’t have a default value here; we’re assuming that content contains the nodes ...