The window manager uses the first request to intercept any request for mapping top-level windows (children of the root window). Whenever another application requests the mapping of a top-level window, the server does not do it but sends an event to the window manager instead. Most window managers reparent the window: they create a larger top-level window (called the frame window) and reparent the original window as a child of it. Graphically, this corresponds to placing the original window inside the frame window. The space of the frame window that is not taken by the original window is used for the decorative frame around the window (the “border” and the “title bar”).