<nic(a)niss.ac.uk> writes:
allow-deletion-of-last-visible-frame t
C-x 5 0 works when another frame is open in another workspace
allow-deletion-of-last-visible-frame nil
C-x 5 0 _fails_ when another frame is open in another workspace
(Attempt to delete last or iconified frame)
The "X" (kill/close thing) button in the window title bar works
Note that "X" will always work because it invokes the FORCE argument
in delete-frame. Try pressing `C-h c' followed by the click on that
"X".