I have just found this: http://msdn.microsoft.com/en-us/library/ms977865.aspx
This MSDN article describes Microsoft Internet Explorer 6 behavior used to implement a demo WYSIWYG XML document editor, shows features that make WYSIWYG XML content editing easy and familiar to word processor users, and makes native XML editing available with edit view icons to access control attributes or fields in the underlying XML document.
I find this is a really cool and seemingly useful technology!
Is there any real project out there that does this?