New Editor: creates a second Score View which opens in a second tab behind the current editor field.
Navigation: allows you to activate and switch between editors. Activated editors can be minimized and maximized. You can choose the previous perspective, editor, or view.
Preferences: Here you can also change preferences for MEISE under "Meise Preferences", e.g. to require the Lab to use the MEISE perspective when opening a MEI document.