Is there a list identifying the "objects" that the terminal returns with my
query ?
They are under org.gnome.gnome-panel.layout.objects in dconf. You can use the
dconf editor that comes by default.
All produce the same set of choices (add to panel, properties, and new panel)
which I have long since exhausted, because they do not include "['menu-bar',
'home', 'abrowser', 'window-list', 'notification-area', 'indicators',
'show-desktop']"
Well, they should be there. Maybe under other names (maybe "notification
area").