Projected windows have three sashes. The top sash doesn't move. The bottom two sashes swing open like awning windows, but in opposite directions.
The topic for each kind of Window describes its unique controls and behavior. Most Window parameters are common to all kinds of Windows,see Windows
Width: Sets the width of the rails and panels in the sashes.
Middle Height: Sets the height of the middle sash, relative to the window’s frame.
Bottom Height: Sets the height of the bottom sash, relative to the window’s frame.
Open: Specifies the percent that the window is open.
Generate Mapping Coords: Assigns mapping coordinates to the window.
For an explanation of how to create a Window, see Windows