Location: 13 Special Construction
When using a thin wall for casing or paneling, a window for cutting the outside of an arch casing. You can set the height and the width. You can choose to extend the hole on either side of the arch to cut more wall.
Like the Openings in the Archicad library, you can preview the shape of the window in the settings box elevation view.
Here's what it's for. I used an Archicad library arch opening for the inside.