The display of a door/window assembly depends on the direction from which you view the door/window assembly. In plan view, the door/window assembly object is displayed as parallel lines with vertices marking the grid lines, as an architect would typically draw a door/window assembly. In 3D view, the door/window assembly object is displayed as it would appear in the real world, with surfaces showing length, thickness, and height. You control what you want to display in each particular view.
By default, the display of all infills, frames, and mullions is controlled by the display properties of the default infill, default frame, and default mullion. However, you can add individual element definitions as components with separate display properties. For example, if you define two infills called stone panel and glass panel, by default they are both controlled by the default infill display properties. But you can add each definition as a new display component and then control the display properties separately.
You can use materials to control the display of both default and custom infills, frames, and mullions. When you assign materials to the element definitions you create, you do not need to define these definitions as custom display components.