Roles as described in T721.
UserStory
Robert opens Roundcube Files and navigates into a shared a folder. The file listing shows that Susy is currently editing a file.
Robert opens the file (doubleclick) to join Susy in the session.
They work on the file together, and when done, Susy selects "Save" and the file is updated in permanent storage and the Roundcube Files listing
reflects the new modified timestamp.