Xalan-Java (named after a rare musical instrument) fully implements XSL Transformations (XSLT) Version 1.0 and the XML Path Language (XPath) Version 1.0. XSLT is the first part of the XSL stylesheet language for XML. It includes the XSL Transformation vocabulary and XPath, a language for addressing parts of XML documents. For links to background materials, discussion groups, frequently asked questions, and tutorials on XSLT, see Getting up to speed with XSLT.

XSL also includes a vocabulary for formatting documents, which is not part of Xalan-Java. For more information, see Extensible Stylesheet Language (XSL) Version 1.0 and the Apache XML FOP (Formatting Objects Project).

You use the XSLT language to compose XSL stylesheets. An XSL stylesheet contains instructions for transforming XML documents from one document type into another document type (XML, HTML, or other). In structural terms, an XSL stylesheet specifies the transformation of one tree of nodes (the XML input) into another tree of nodes (the output or transformation result).

The XSL stylesheet may generate and refer to cascading style sheets (CSS) as part of its output.

In the following example, the foo.xsl stylesheet is used to transform foo.xml into foo.out:

foo.xml:

	<?xml version="1.0"?> <doc>Hello</doc>

foo.xsl:

	<?xml version="1.0"?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"> <xsl:template match="doc"> <out><xsl:value-of select="."/></out> </xsl:template> </xsl:stylesheet>

foo.out:

	<out>Hello</out>

By default, Xalan-Java uses Xerces-Java, and it may be configured with system properties to work with other XML parsers (see Plugging in a Transformer and XML parser). The input may be submitted in the form of a stream of XML markup (from a URI, a character or byte stream, or another transformation), a SAX InputStream, or a DOM Node.

Xalan-Java performs the transformations specified in the XSL stylesheet and packages a sequence of SAX events that may be serialized to an output stream or writer, used to build a DOM tree, or forwarded as input to another transformation.

• Includes an Interpretive processor for use in a tooling and debugging environment and a Compiling processor (XSLTC) for use in a high performance runtime environment.
  
  
• Implements the relevant W3C specifications: XSL Transformations (XSLT) Version 1.0 and XML Path Language (XPath) Version 1.0.
  
  
• Implements TrAX (Transformation API for XML), now part of Java API for XML Processing 1.2, and builds on SAX 2 and DOM level 2.
  
  
• May be configured to work with any XML parser, such Xerces-Java, that implements Java API for XML Processing 1.2 (see Plugging in an XML parser).
  
  
• Can process Stream, SAX or DOM input, and output to a Stream, SAX or DOM.
  
  
• Transformations may be chained (the output of one transformation may be the input for another).
  
  
• May be run from the command line for convenient file-to-file transformations.
  
  
• Includes an applet wrapper.
  
  
• May be used in a servlet to transform XML documents into HTML and serve the results to clients.
  
  
• Supports the creation of Java and scripting language extensions. and provides a growing library of extension elements and functions.

For instructions and some suggestions about how to get started using the XSLT Interpretive processor, see Getting Started with Interpretive Processing.

For instructions and some suggestions about how to get started using the XSLT Compiling processor, see Getting Started with XSLTC.

If you are still working through the details of the XSLT spec (the W3C 1.0 Recommendation), you may want to consult one or more of the following:

• XSLT - XSL Transformations in The XML Revolution: Technologies for the future Web by Anders Møller and Michael I. Schwartzbach (Web pages, but designed for sequential reading)
• Crane Softwright's Free preview of Practical Transformation Using XSLT and XPath
  
  
• Doug Tidwell's XSLT, O'Reilly, 2001
  
  
• Bob Ducharme's XSLT Quickly, Manning Publications, 2001
  
  
• John Robert Gardner and Zarella Rendon's XSLT and XPath: A Guide to Transformations, Prentice-Hall, 2001
  
  
• Michael Kay's XSLT Programmer's Reference, 2nd ed., Wrox Press, 2001
  
  
• Steven Holzner's Inside XSLT, New Riders, 2001
  
  
• Neil Bradley's XSL Companion, Addison-Wesley, 2000
  
  
• Khun Yee Fung's XSLT: Working with XML and HTML, Addison-Wesley, 2001
  
  
• Dave Pawson's XSL Frequently Asked Questions to search out particular answers and techniques
  
  
• Miloslav Nic's XSL Tutorial, a collection of stylesheet examples
  
  
• Elliotte Rusty Harold's Chapter 14 of the XML Bible: XSL Transformations
  
  
• The Mulberry XSL-List -- Open Forum on XSL (of interest to XSL users at all levels)
  
  
• Objects by Design's Transforming XMI to HTML (oriented towards XMI, "an XML-based, stream representation of a UML model," but also covers "generic" XML transformations) and their related XSLT by Example
  
  
• OASIS (the Organization for the Advancement of Structured Information Standards): Extensible Stylesheet Language (XSL) by Robin Cover
  
  
• Donald Ball's A Guide to XML and XSL for Designers
  
  

When you come across other useful introductory or background materials, please email Xalan Development Mailing List, so we can add them to this list.

XSLT Namespace

The XML namespace for XSLT. An XML namespace is a collection of element and attribute names, identified by a Unique Resource Identifier (URI), which often takes the form of a URL, but is really just a unique string, not a pointer to a web page. The XSLT namespace URI is http://www.w3.org/1999/XSL/Transform. In each XSLT stylesheet, you must declare this namespace in the stylesheet element tag and bind it to a local prefix. Like the XSLT specification, we always use xsl as the XSLT namespace prefix in our descriptions and examples, although you are free to bind any prefix to this namespace.

XSL Instruction

Any tag associated with the XSLT namespace.

Template

An element, usually with child elements, that specifies a "rule" or set of instructions to perform when a particular kind of node is encountered in the source tree.

XSL Template Instruction

Any tag that occurs inside an xsl:template element and is associated with the XSLT namespace.

Source Tree

The XML tree input to the XSL process.

Result Tree

The tree that is output by the XSL process.

Match Pattern

The part of a template that defines the kind(s) of nodes to which the template applies.

For more definitions of XSLT terminology, see Dave Pawson's XSLT Terminology Clarification and the Glossary in Michael Kay's XSLT Programmer's Reference.