VASSAL Reference Manual
This trait allows you to cluster menu items associated with other traits into a sub-menu of the game piece’s right-click context menu.
Provide a name for the menu and the exact menu text of the menu items that should be moved to the sub-menu.
Sub-menus may contain other sub-menus to any nesting level.
EXAMPLE: If a game piece has three separate layer traits with the corresponding activate commands Entrench, Fortify, and Blockade, then those menu items can be gathered under a single sub-menu named Defense by creating a Sub-Menu trait with menu name "Defense" and sub-commands "Entrench", "Fortify" and "Blockade".
SEE ALSO: Menu Separator