XML in a Nutshell, 3rd Edition

Selecting the Context Node with .

Finally, the single period (.) indicates the context node. In XSLT this is most commonly used when you need to take the value of the currently matched node. For example, this template rule copies the content of each comment in the input document to a span element in the output document:

<xsl:template match="comment( )">
  <span class="comment"><xsl:value-of select="."></span>
</xsl:template>

The . given as the value of the select attribute of xsl:value-of stands for the matched node. This works equally well for element nodes, attribute nodes, and all the other kinds of nodes. For example, this template rule matches name elements from the input document and copies their value into strongly emphasized text in the output document:

<xsl:template match="name">
  <strong><xsl:value-of select="."></strong>
</xsl:template>