There are two activation sequences for menus which seem to be impossible
without revising most of the Gtk menu widgets. These are conditional
cascading menus and menus as found on the MacOS Apple menu where an
item with a submenu may also be activated.

Common to both of these is that an item with a submenu can be activated.
This alone seems impossible with the current system. Redoing the menu
system to allow just this would make the MacOS-like item possible.
However, such an item is of limited utility as it is only suited for
MacOS Apple menu- or Windows Start menu-like menus, and perhaps
bookmark menus. The MacOS implementation is poor in that there is
no visual indication of the affordance.

Conditional cascading menus, which may be found on OS/2 and IceWM, do
provide visual indication of what they afford. What they afford is
simpler activation of a particular item from a submenu (the default)
by allowing it to be activated from the item which has the submenu.
Unlike the MacOS menu, the submenu is not posted when the item is
normally selected, and the action which the item with a submenu takes
is always one present and indicated on the submenu. Posting of the
submenu is afforded by delay, by keyboard navigation as for ordinary
submenus off of items, by key-modified mouse action (holding Ctrl
down while mousing in IceWM), and by moving into the region of the
submenu-indicating arrow. (On OS/2, the region is not pre-lighted
until it the submenu is shown. IceWM pre-lights the entire item, but
that may be a bug in my copy.) The difficulty in navigating to
the smaller region to show the submenu is relieved somewhat by the
other methods. The slight cost incurred there is offset by the great
boon in simplicity and accessibility compared to other methods of
affording similar actions such as right-click menus on menu items.

The simplicity is found in the reduction of items which are presented
to the ordinary user. Users seeking non-default actions will be able
to see more items, but not have to see so many at once. An example
is the File->New item in an office suite. Creating new blank documents
of the same type as the office app in use would (presumably) be the
default action; while creating new documents from templates or
of types handled by other apps in the suite would be items in the
submenu. A similar use holds for browsers and Internet suites.
For those not using such apps, benefit is to be found in the reduction
of items on file manager icon pop-ups. Here the Open item defaults
to a particular action and the submenu allows for others. This spares
presentation of two or even more items on the popup which are needed
otherwise. Internet suites also benefit here and office suites are
allowed a better place to put a list of recent files.


A brief and perhaps more lucid (read: has screenshots) presentaion
of conditional cascading menu items may be found here:

  http://www.phys.lsu.edu/~merchan/CGMenus/Beta/index.html

Given a casual analysis of the elements and informal survey of and
card sorts with office users of Microsoft products, I am confident
that a thorough analysis and formal user testing will show that
conditional cascading menus are of more than sufficient benefit to
be deployed desktop-wide.