The footnote preview

footnotePreview<Message>() is drawn while the caret is in a footnote reference (RichText.footnoteAt), and is empty everywhere else, so a caller can anchor it at the selection and draw it always. It shows the note's text ("No note yet" when there is none), Go to note, which sends opened(definition) (the caller usually gives the editor the focus there with focus), and the label as a field that sends the editor's RenamedFootnote when it changes.