I'm looking for way to format the XML syntax displayed in a pre tag on my sandbox web.
If you know how, please show me.
You can have a look at Hyperlight or GeSHi (in PHP).
Perhaps you'd prefer to use a Javascript script: consider this list.
If you want syntax highlighting then this is the only script / plugin you need -> http://alexgorbatchev.com/SyntaxHighlighter/
This is javascript though and will format it within the browser