The File Menu

Save — save the layout.

Compile layout — this option is only enabled where direct control of layout compilation is required.

Undo last save — restore the layout to its state before the last save (see below).

Exit — exit the layout editor.

Whenever a layout is saved, a backup copy is kept of its previous saved state. The Undo last save action restores this backup copy. Don’t use this to undo changes made since the last save — that can be achieved simply by exiting the editor without saving.