Creating and validating XML documents is usually only half the battle. After you’ve composed your document, you’ll want to publish it. Publishing, for our purposes, means either print or web publishing. For XML documents, this is usually accomplished with some kind of stylesheet. In some environments, it is now possible to publish an XML document on the Web simply by putting it online with a stylesheet.
1. A Survey of Stylesheet Languages
Over the years, a number of attempts have been made to produce a standard stylesheet language and, failing that, a large number of proprietary languages have been developed. Since this book was first written, three standards have emerged as the clear frontrunners:
The W3C CSS Working Group created CSS as a style attachment language for HTML. It has also been advanced as a stylesheet language for XML. Some browsers will style arbitrary XML with CSS and some commercial products exist that will render XML+CSS either online or in print.
XSLT 1.0 is well established and is probably the most common styling technology for DocBook. XSLT 2.0 offers a number of important new features (at the expense of some complexity, naturally) and is growing in popularity.
It’s worth observing that there are two, related technologies in play here. XSLT 1.0 and 2.0, the transformation languages, and XSL Formatting Objects (XSL-FO). XSL-FO is an XML vocabulary for describing constraints on page layout.
1.1. Stylesheet Examples
1 <para>This is an example paragraph. It should be presented in a 2 reasonable body font. <emphasis>Emphasized</emphasis> words should be printed in italics. A single level of 4 <emphasis>Nested <emphasis>emphasis</emphasis> should also be supported.</emphasis> 6 </para>
1.1.1. CSS stylesheet
CSS stylesheets consist of selectors and formatting properties, as shown in Example 4.1, “A fragment of a CSS stylesheet”.
As this edition is being written, namespace selection in CSS, while widely supported, is still a Candidate Recommendation at W3C.
1.1.2. XSL stylesheet
XSL stylesheets are XML documents, as shown in Example 4.2, “A fragment of an XSL stylesheet”. The element in the XSL stylesheet that controls the presentation of specific elements is the xsl:template element.
A complete stylesheet for generating an entire XSL-FO document would require additional boilerplate text not shown.
XQuery is expressed in a mixture of text and XML fragments, as shown in Example 4.3, “A fragment of XQuery”.
A complete query for generating an XSL-FO document would require additional boilerplate text not shown.
2. Using XSL to Publish DocBook Documents
The community of people using DocBook has created a set of open source XSL stylesheets that are maintained at Sourceforge.net. These stylesheets can be used to transform DocBook XML into a wide variety of formats, including HTML, Javahelp, XSL-FO (for processing into print), ePub, and HTML help.
For a detailed discussion of using XSL to publish DocBook documents, see DocBook XSL: The Complete Guide [Stayton07].