Select the Wall with the Window in it and go to the 3D Window.
In the 3D Window select the Window.
If the "Fully Editable" option is set to ON, then you will see, besides the usual corner hotspots of the Window, one or maybe more other hotspots. These are the 3D editing hotspots and their color and shape (diamond) is usually different from the normal hotspots.
You can click and drag these hotspots to modify various ascepts of the Window geometry. For example, with most Windows you will have a 3D editable hotspot that will let you graphically modify the opening angle of the Window Sash.
If the "Fully Editable" option is set to OFF, these Hotspots are not visible and you cannot use them for graphical editing in 3D.
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