collapse_expand (PopUpMenu)

         # File lib/json/editor.rb, line 444
    444:       def collapse_expand(item)
    445:         if current = selection.selected
    446:           if row_expanded?(current.path)
    447:             collapse_row(current.path)
    448:           else
    449:             expand_row(current.path, true)
    450:           end
    451:         else
    452:             toplevel.display_status("Append a node into the root first!")
    453:         end
    454:       end