XSL, the style sheet language of XML is far more sophisticated than CSS.

CSS - The Style Sheet of HTML

Because HTML uses predefined tags, the meanings of these tags are well understood: The <p> element defines a paragraph and the <h1> element defines a heading, and the browser knows how to display these elements.

Adding display style characteristics to HTML elements with CSS is a simple process. Telling the browser to display each element using a special font or color, is easy to do and easy for a browser to understand. 

XSL - The Style Sheet of XML

Because XML does not use predefined tags (we can use any tags we want), the meanings of these tags are not understood: <table> could mean an HTML table or maybe a piece of furniture. Because of the nature of XML, the browser does not know how to display an XML document.

In order to display XML documents, it is necessary to have a mechanism to describe how the document should be displayed. One of these mechanisms is CSS, but XSL (the eXtensible Stylesheet Language) is the preferred style sheet language of XML, and XSL is far more sophisticated than the CSS used by HTML.

XSL - More than a Style Sheet

XSL consists of three parts:

• a method for transforming XML documents
• a method for defining XML parts and patterns
• a method for formatting XML documents

If you don't understand the meaning of this, think of XSL as a language that can transform XML into HTML, a language that can filter and sort XML data, a language that can address parts of an XML document, a language that can format XML data based on the data value, like displaying negative numbers in red, and a language that can output XML data to different devices, like screen, paper or voice. 

XSL Languages

 XSL actually consists of three languages. The most important is XSLT.

XSL is Three Languages

XSL actually consists of three languages:

• XSLT is a language to transform XML
• XPath is a language to define XML parts or patterns
• XSL Formatting Objects is a language to define XML display

XSLT is a language for transforming XML documents into other types of documents, or into other XML documents.

XPath is a language for addressing parts of an XML document. XPath was designed to be used by XSLT.Formatting is the process of turning the result of an XSL transformation into a suitable output form for a reader or listener.

XSLT - XSL Transformations

XSLT is the most important part of the XSL Standard. It is the part of XSL that is used to transform an XML document into another XML document, or another type of document.

XSLT can be used to transform an XML document into a format that is recognizable to a browser. One such format is HTML. Normally XSLT does this by transforming each XML element into an HTML element.

XSLT can also add completely new elements into the output file, or remove elements. It can rearrange and sort the elements, and test and make decisions about which elements to display, and a lot more.

A common way to describe the transformation process is to say that XSL uses XSLT to transform an XML source tree into an XML result tree (or an XML source document into an XML result document)

How does it work?

In the transformation process, XSLT uses XPath to define parts of the source document that match one or more predefined templates. When a match is found, XSLT will transform the matching part of the source document into the result document. The parts of the source document that do not match a template will (as a general rule) end up unmodified in the result.

This Tutorial will focus on XSLT and XPath

Most of the chapters in this tutorial will focus on XSLT and XPath. We will use XSLT to define XML transformations and XPath to define the matching patterns for the transformations.

Even though XSL consists of three different parts with three different names, we will use the general term XSL in this tutorial.

XSL Browsers

Very few browsers support XSL at the moment.

In this tutorial we will use Internet Explorer 5.0 to demonstrate XSL.

The Internet Explorer XML Parser

In order to process an XML document using XSL, you need an XML parser with an XSL Engine. Internet Explorer 5.0 is currently the only widely available browser that contains an XML parser with an XSL engine.

At the moment, the example code in this tutorial will only work in Internet Explorer 5.0 or later. 

The Internet Explorer XSL Engine

XSL in Internet Explorer 5.0 is not 100% compatible with the latest released W3C XSL standard.

Internet Explorer 5 was released before the XSL standard was completely settled (when the XSL standard was still a W3C Working Draft), but Microsoft has promised to solve this problem in the next release.

This is the standard way from the W3C XSL Recommendation:

 This is the (incorrect) Internet Explorer way (from the XSL Working Draft):

Internet Explorer MSXML

MSXML 2.0 is the name of the XML parser that shipped with IE 5.0.

MSXML 2.5 is the name of the parser that shipped with Windows 2000.

MSXML 3.0 is the latest release of the XML parser. It can be downloaded from Microsoft, and will ship with future versions of Internet Explorer and Windows.

According to Microsoft, MSXML 3.0 is 100% compatible with the official W3C XSL Recommendation:

"MSXML 3.0 offers a significant advancement over MSXML 2.5: server-safe HTTP access, complete implementation of XSLT and XPath, changes to SAX (Simple API for XML), higher conformance with W3C standards, and a number of bug fixes"

For more info:
http://msdn.microsoft.com/xml/general/xmlparser.asp

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