As a user, I'd like to have a way to determine what document elements or layout boxes are in the view port. I may need them in order to:

- Modify something else in the UI depending on them. For example, if a hyperlink or bookmark is scrolled in the viewport, enable buttons outside RichTextBox that execute specific actions.
- Implement formatting changes to the visible elements only in scenarios like a code editor.

Right now, the only way to obtain the visible boxes is to implement a UI layer, however, layers are intended for scenarios in which you'd like to modify the presentation of the control's content and may not be a good idea to utilize them for formatting changes or other actions.