Please, note that RadEditor is an XHTML/HTML editor but not XML editor and there are limitations because the browser support only HTML tags.
You can use the DOM Inspector module
to see breadcrumb details about your XML tags. See the following video for more information: http://screencast.com/t/DXtu7rvYbwT7
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed