XML in a Nutshell, 3rd Edition

The Default Template Rule for Element and Root Nodes

The most important template rule is the one that guarantees that children are processed. Here is that rule:

<xsl:template match="*|/">
  <xsl:apply-templates/>
</xsl:template>

The asterisk * is an XPath wildcard that matches all element nodes, regardless of what name they have or what namespace they’re in. The forward slash / is an XPath expression that matches the root node. This is the first node the processor selects for processing, and, therefore, this is the first template rule the processor executes (unless a nondefault template rule also matches the root node). Again, the vertical bar combines these two expressions so that the rule matches both the root node and element nodes. In isolation, this rule means that the XSLT processor eventually finds and applies templates to all nodes except attribute and namespace nodes because every nonattribute, non-namespace node is either the root node, a child of the root node, or a child of an element. Only attribute and namespace nodes are not children of their parents. (You can think of them as disinherited nodes.)

Of course, templates may override the default behavior. For example, when you include a template rule matching person elements in your stylesheet, then children of the matched person elements are not necessarily processed, unless one of your own template rules says to process them.