What is the primary function of a window frame?

The primary function of a window frame is to hold the glass in place securely. A well-constructed frame ensures that the glass pane is properly fitted and stabilized within the overall structure of the window. This function is crucial not only for maintaining the integrity of the glass against external factors but also for providing insulation and preventing air and water penetration into the building.

While the frame does serve additional functions, such as supporting the window sash and contributing to aesthetic appearance or providing some protection from weather conditions, its fundamental purpose remains centered around securing the glass. Therefore, the emphasis on the frame's role in holding the glass is what distinguishes it as the most accurate answer.