These would be notes to the current writer or future writers working on the publication. Examples are notes about conditions that need to be applied, topics that are being shared between the current publication and other publications, and so on. I think another pane in the lower-left part of the display, below the TOC, would be a good place for notes. Or perhaps a new "Notes" tab, including a number in parentheses that indicates the number of notes saved, so the writer can easily see that notes have been saved for the publication.