duplicate-window

This command is also known as split-current-window. Creates a new window and displays the same buffer in both windows. The new window presents the object in the same view as the original window. Although a buffer has but one structural selection, each window displaying a buffer has its own insertion cursor and can be scrolled independently. The new window is placed in its own auto-scroll set, so changing the structural selection in the new window does not cause the original window to scroll.