The browser will display the XML document as is. If you need to extract parts of the document and format them in a different order you will need to use XSL. Infact the browser uses a dummy XSL that simply traverses all the nodes and prints the contents.
The capability of a browser to display an XML document should not be considered as an alternative to using XSLs. For example, a browser is of no use if you have to generate the formatted XML, say in the pdf format or MSWord format on the server!
HTH
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Ajith Kallambella M. Sun Certified Programmer for the Java�2 Platform.
IBM Certified Developer - XML and Related Technologies, V1.