Mike Brown and Jeni Tennison have developed a stylesheet for
pretty printing XML.
The stylesheet creates an HTML and CSS representation. A version that produces
plain ASCII output is also available.
Announcing the stylesheet, Mike Brown notes:
The intended audience for this is beginners needing help with
XPath/XSLT model visualization, as well as advanced XML application
developers. (It is quite handy for debugging an XSLT processor
implementation, for example).