Although the focus tends to be on writing and validating XML documents, in the end the information in a document must be presented to a user. Although some web browsers can display XML documents directly, most users would prefer not to have to interpret the raw XML source code. The mechanisms for making XML presentable to end users are generically called stylesheets.
One of the first (and most widely supported) stylesheet languages is Cascading Style Sheets (CSS). CSS was originally intended for use with HTML documents to allow authors to separate presentation information from the structural details of the HTML page. When XML began to be widely used, CSS was extended to support formatting and displaying XML documents. IE 5.0 included support for associating CSS stylesheets with XML documents. Unfortunately, because CSS doesn't support structural transformation of the target document, it's being deprecated as a display technique for XML documents.
Another more common method for displaying XML data is to transform it into HTML (using XSLT) and then present it using a web browser.