The xsl:apply-templates Element

The template I used in the previous section applied only to one node, the root node, and it performed a trivial action, replacing the entire XML document with an HTML document. However, you can also apply templates to the children of a node that you've matched, and you do that with the <xsl:apply-templates> element.

For example, say that I want to convert ch13_01.xml to HTML. The document node in that document is <PLANETS> , so I can match that element with a template, setting the match attribute to the name of the element I want to match. Then I can replace the <PLANETS> element with an <HTML> element, like this:

 <?xml version="1.0"?>  <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">  <xsl:template match="PLANETS">   <HTML>   .   .   .   </HTML>   </xsl:template>  .     .     . </xsl:stylesheet>

But what about the children of the <PLANETS> element? To make sure they are transformed correctly, you use the <xsl:apply-templates> element this way:

 <?xml version="1.0"?>  <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">     <xsl:template match="PLANETS">         <HTML>  <xsl:apply-templates/>  </HTML>     </xsl:template>     .     .     . </xsl:stylesheet>

Now you can provide templates for the child nodes. In this case, I'll just replace each of the three <PLANET> elements with some text that I place directly into the template for the <PLANET> element:

Listing ch13_06.xsl

 <?xml version="1.0"?> <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">     <xsl:template match="PLANETS">         <HTML>             <xsl:apply-templates/>         </HTML>   </xsl:template>  <xsl:template match="PLANET">   <P>   Planet data will go here....   </P>   </xsl:template>  </xsl:stylesheet>

And that's it. Now the <PLANETS> element is replaced by an <HTML> element, and the <PLANET> elements are also replaced:

 <HTML>      <P>         Planet data will go here....     </P>     <P>         Planet data will go here....     </P>     <P>         Planet data will go here....     </P> </HTML>

You can see that this transformation works, but it's still less than useful; all we've done is replace the <PLANET> elements with some text. What if we want to access some of the data in the <PLANET> element? For example, say that we want to place the text from the <NAME> element in each <PLANET> element in the output document:

 <PLANET>  <NAME>Mercury</NAME>  <MASS UNITS="(Earth = 1)">.0553</MASS>     <DAY UNITS="days">58.65</DAY>     <RADIUS UNITS="miles">1516</RADIUS>     <DENSITY UNITS="(Earth = 1)">.983</DENSITY>     <DISTANCE UNITS="million miles">43.4</DISTANCE><!--At perihelion--> </PLANET>

To gain access to this kind of data, you can use the select attribute of the <xsl:value-of> element.