Templates à la Mode Invoking Templates by Name

page 62 xsl:template match=h1 mode=process-text -- Template to process the h1 element along with the rest -- -- of the document -- xsl:template We can then start applying templates with the mode attribute: xsl:template match= html body h1Table of Contentsh1 ul xsl:apply-templates select=h1 mode=build-toc ul xsl:apply-templates select= mode=process-text body html xsl:template This style of coding makes maintenance much easier; if the table of contents isnt generated correctly, the templates with mode=build-toc are the obvious place to start debugging. See Chapter 9 for a more detailed discussion of the mode attribute.

4.4 Parameters

The XSLT xsl:param and xsl:with-param elements allow you to pass parameters to a template. You can pass templates with either the call-template element or the apply- templates element; well discuss the details in this section.

4.4.1 Defining a Parameter in a Template

To define a parameter in a template, use the xsl:param element. Heres 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, isnt 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 Section 3.3 in Chapter 3 . page 63 Notice that in the previous sample, we put single quotes around the value blue , but we didnt do it around the value 150 . Without the single quotes around blue , the XSLT processor assumes we want to select all the blue elements in the current context, which is probably not what we want. The XSLT processor is clever enough to realize that the value 150 cant be an XML element name the XML 1.0 Specification says element names cant begin with numbers, so we dont need the single quotes around a numeric value. Try to keep this in mind when youre using parameters. Youll probably forget it at some point, and youll probably go nuts trying to figure out the strange behavior youre getting from the XSLT processor. The second way to define a default value for a parameter is to include content inside the xsl:param element: template name=addTableCell xsl:param name=bgColor xsl:textbluexsl:text xsl:param xsl:param name=width xsl:value-of select=7+8xsl:text0xsl:text xsl:param xsl:param name=content td width={width} bgcolor={bgColor} xsl:apply-templates select=content td template In this example, we used xsl:text and xsl:value-of elements to define the default values of the parameters. Out of sheer perverseness, we defined the value of width as the concatenation of the numeric expression 7+8 , followed by the string 0. This example produces the same results as the previous one.

4.4.2 Passing Parameters