Webmaster in a Nutshell, Third Edition

Templates and Patterns

An XSLT style sheet transforms an XML document by applying templates for a given type of node. A template element looks like this:

<xsl:template match="pattern"> 
   ...
</xsl:template>

where pattern selects the type of node to be processed.

For example, say you want to write a template to transform a <para> node (for paragraph) into HTML. This template will be applied to all <para> elements. The tag at the beginning of the template will be:

<xsl:template match="para">

The body of the template often contains a mix of template instructions and text that should appear literally in the result, although neither are required. In the previous example, we want to wrap the contents of the <para> element in <p> and </p> HTML tags. Thus, the template would look like this:

<xsl:template match="para">
   <p><xsl:apply-templates/></p>
</xsl:template>

The <xsl:apply-templates/> element recursively applies all other templates from the style sheet against the <para> element (the current node) while this template is processing. Every style sheet has at least two templates that apply by default. The first default template processes text and attribute nodes and writes them literally in the document. The second default template is applied to elements and root nodes that have no associated namespace. In this case, no output is generated, but templates are applied recursively from the node in question.

Now that we have seen the principle of templates, we can look at a more complete example. ...