On what does the window rest when closed?

The window rests on the sash channel when it is closed. The sash channel is designed specifically to provide a guided path for the window sash, ensuring that the window can slide open and shut smoothly. It's an integral part of the window's assembly that helps secure the glass in place and provides structural support when the window is closed, preventing it from falling out or becoming misaligned. The sash channel is crucial in maintaining the overall functionality and efficiency of the window, as well as contributing to weather-tightness and insulation.

Other options like the frame and glass track serve different purposes in the window assembly. The frame provides the overall structure to which the window is attached, while the glass track would typically refer to a component that allows sliding windows to operate but is not the same as where the window sash rests when fully closed. A window ledge is more of a support surface that can be found on the exterior or interior under the window but does not serve the role of securing the window in place while closed.