XSLT (Extensible stylesheet language transformation) is a great way to transform XML files to other XML files – for example converting XML to XHTML to be viewed in a browser. A RSS feed is just an XML that your browser converts to XHTML using a XSL file.
If you’ve ever used XML+XSLT in your browser, you know that using View Source presents you with the original XML file, not the HTML that you might have expected; this makes debugging XSL transformations somewhat difficult.
I have found however a nice little tool for Internet Explorer that lets you validate the XML and view the XSL transformation result. After installing it, you can select View XSL Output via right-click on page. I know programs like XML Spy or Stylus Studio have advanced XSLT debuggers, but sometimes just being able to see the transformation result is enough.