XML alone will not display a page. You must use a formatting technology, such as CSS or XSL to display XML-tagged documents in a Web browser.
XML is about separating structure and format. An XML document doesn't know anything about how to display itself. It relies on other technologies for this.
Although XML does not deal with form, it contains a great deal of information about the document and its elements. This, when combined with style tools, gives you a whole new strength and flexibility in displaying your documents without having to maintain multiple copies of the document.
Extensible Stylesheet Language, XSL, is the future of XML display. It is an XML-based languages for expressing stylesheets.
With XSL, you can make context-sensitive display decisions. For example, you could automatically display the document one way in a Web browser and another on a PDA.
XSL can also transform XML into HTML, so that older browsers can view XML documents.
Cascading Style Sheets, CSS-1 and CSS-2, are the current way to display XML documents in a Web browser. CSS is a means of assigning display values to page elements.
If you are going to be working with XML and you will be concerned with displaying pages, learn CSS. The CSS Reference Guide contains a guide to the CSS-1 properties.
Behaviors are a non-standard, IE5 technique that lets you do some interesting display actions with XML tags. They combine scripting and CSS in a component file. This component can be attached to a particular tag and used in many different documents. The Behaviors Library shows some of the things you can do with this technique.