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menu-multiple_selection
menu <- multiple_selection: multiple=bool
If @on, any item can be either selected or deselected. It @off, exactly one item has status menu_item<->selected. A marked menu shows radio buttons if @off and check boxes if @on. A cycle menu always has a single selection.

If @on, Alt-click or double-click on an item selects only this item. Doing so again on this item while it is the only one selected restores the selection from before. The message of the menu is called as for a click on the item.

See also
menu_item-selected
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