After that little aside to understand a couple of important areas of XSLT, we can get back to what XSLT can do for us. Now that we have covered the most important elements, we can cover the most important functions.

Have you ever accidentally (or deliberately) applied an empty stylesheet to a document?

The following five elements allow us to control execution within a template in a manner analogous to procedural languages. These are <xsl:if>, <xsl:choose>, <xsl:when>, <xsl:otherwise>, and <xsl:for-each>.

In this section, we will recap all the elements we have used so far, and meet several others. With these you will be able to create the vast majority of the XSLT stylesheets you might want.

You can get a long way with XML without any knowledge of namespaces, but you won't get far with XSL!

In this chapter we will provide you with enough information to start building useful XSLT stylesheets. I will introduce a number of the elements that make up the language, providing examples of their use.

In this final section of this chapter I shall try and identify what tasks XSLT is good at, and by implication, tasks for which a different tool would be more suitable. I shall also look at alternative ways of using XSLT within the overall architecture of your application.

What are the most significant characteristics of XSLT as a language, which distinguish it from other languages? In this section I shall pick three of the most striking features: the fact that it is written in XML syntax, the fact that it is a language free of side-effects, and the fact that processing is described as a set of independent pattern-matching rules.

Like most of the XML family of standards, XSLT was developed by the World Wide Web Consortium (W3C), a coalition of companies orchestrated by Tim Berners-Lee, the inventor of the web. There is an interesting page on the history of XSL, and styling proposals generally, at http://www.w3.org/Style/History/.

XSLT is published by the World Wide Web Consortium (W3C) and fits into the XML family of standards, most of which are also developed by W3C. In this section I will try to explain the sometimes-confusing relationship of XSLT to other related standards and specifications.

By now you are probably wondering exactly how XSLT goes about processing an XML document in order to convert it into the required output.

XSLT, which stands for eXtensible Stylesheet Language: Transformations, is a language which, according to the very first sentence in the specification (found at http://www.w3.org/TR/xslt), is primarily designed for transforming one XML document into another.