on-demand in labelled-menu-item<%>
Normally called when the user clicks on the menu bar containing the item (before the user sees any menu items), just before the popup menu containing the item is popped up, or just before inspecting the menu bar containing the item for a shortcut key binding.
A
on-demand in menu-item-container<%> method can be overridden in such a way that the container does not
call the
on-demand method of its items.
( -> voidsend a-labelled-menu-item on-demand)
Calls the demand-callback procedure that was provided when the
object was created.