is a control that is able to display and edit rich-text content including formatted text arranged in pages, paragraphs, spans (runs), tables, etc. You can also put UIElements in InlineUIContainers, but they will not be exported as their analogs in HTML. You can read more about this document elements here
When it comes to the designer functionality you have described, the editor does not preserve the initial input when you load an HTML or XAML document and when you export it, the output will be different from the content used to create the document. That is why the control is not very well-suited to be used in such a use-case, as this scenario is not in the targeted scope of the control.
the Telerik team