Summing Up The Tutorial - Page 9

So far, this brief tour has only given you a taste of XSL's capabilities—yet we've already covered the features that will let you do four-fifths of your XSLT work! We've shown you how to:

• delete elements
• rename elements
• reorder elements
• delete attributes
• rename attributes
• convert elements to attributes
• convert attributes to elements
• process elements based on an attribute's value

Before moving on, let's review what the XSLT processor is doing now that you've seen it in action a few times. Imagine that an XSLT processor has just started process-ing the children of the chapter element in the following document,

<book><title>Paradise Lost</title>
  <chapter><title>The Whiteness of the Whale</title>
    <para>He lights, if it were Land that ever burned</para>
    <para>With solid, as the Lake with liquid fire</para>
  </chapter>
  <chapter><title>The Castaway</title>
    <para>Nine times the Space that measures Day and Night</para>
    <para>To mortal men, he with his horrid crew</para>
  </chapter>
</book>

and it's using a stylesheet with the following two template rules to process it:

<!-- xq37.xsl -->

  <xsl:template match="title">
    Title: <xsl:apply-templates/>
  </xsl:template>

  <xsl:template match="chapter/title">
    Chapter title: <xsl:apply-templates/>
  </xsl:template>

(The match pattern "chapter/title" in the second template element shows that this template rule is for the title elements that are children of chapter elements. The first is for all the other title elements.) The diagram in figure 1.7 shows the steps that take place. The chapter title's content is the only text node shown in the source tree; the rest are omitted to simplify the diagram.

1. It finds the first child of the chapter element, a title element node.
2. It checks the stylesheet for a matching template rule. It finds two, and picks the most specific one it can find.
3. Once it's found the best template rule for the node, it gets the template rule's template to add to the result tree.
4. It adds the template, which consists of a text node ("Chapter title:") and the result of processing the template's xsl:apply-templates element to the title element's lone text node child: the string "The Whiteness of the Whale."

   Of course, XSLT can do much more than what we've seen so far. If you'd like more background on key XSLT techniques before you dive into stylesheet development, the following sections of part 2, "XSLT user's guide: How do I work with...," on page 21 of this book are good candidates for "Advanced Beginner" topics:

   • chapter 2, "XPath," on page 23
   • chapter 3, "Elements and attributes," on page 47
   • section 3.6, "Copying elements to the result tree," page 57
   • section 5.1, "Control statements," page 110
   • section 6.1, "HTML and XSLT," page 187
   • section 6.5, "Non-XML output," page 202
   • section 6.6, "Numbering, automatic," page 205
   • section 6.9, "Valid XML output: including DOCTYPE declarations," page 225

   If your stylesheet absolutely depends on these potentially unavailable elements, the xsl:message element can do more than just output a message about the problem: it can abort the processing of the source document with its terminate attribute. (See section 5.4.1, "Runtime messages, aborting processor execution," page 134, for more on the use of xsl:message.)

   Attribute Value Templates - Page 8
   XSLT Quickly