User menus are added to the right of existing menus, and items are
  added at the bottom of the menu.
By default the action character string is treated as R input, being
  echoed on the command line and parsed and executed as usual.
If the menuname parameter of winMenuAddItem does not
  already exist, it will be created automatically.
Normally new submenus and menu items are added to the main console
  menu. They may be added elsewhere using the following special names:
      $ConsoleMainThe console menu (the default)
 
      $ConsolePopupThe console popup menu
 
      $Graph<n>MainThe menu for graphics window <n>
 
      $Graph<n>PopupThe popup menu for graphics window
      <n>
 
  
Specifying an existing item in winMenuAddItem enables the
  action to be changed.
Submenus can be specified by separating the elements in
  menuname by slashes: as a consequence menu names may not
  contain slashes.
If the action is specified as "none" no action is taken:
  this can be useful to reserve items for future expansion.
The function winMenuNames can be used to find out what menus
  have been created by the user and returns a vector of the existing
  menu names.
The winMenuItems function will take the name of a menu and
  return the items that exist in that menu.  The return value is a named
  vector where the names correspond to the names of the items and the
  values of the vector are the corresponding actions.
The winMenuDel function will delete a menu and all of its items
  and submenus.  winMenuDelItem just deletes one menu item.
The total path to an item (menu string plus item string) cannot exceed
  1000 bytes, and the menu string cannot exceed 500 bytes.