XLIB Programming Manual, Rel. 5, Third Edition

16.3 Reparenting

A window manager can decorate windows on the screen with titlebars and place little boxes on the titlebar with which the window can be moved or resized. This is only one possibility, modeled on the user interface on the Macintosh™.

To do this, the window manager creates a child of the root somewhat larger than the top-level window of the application. Then it calls XReparentWindow(), specifying the top-level window of the application as win and the new parent as parent. win and all its descendants will then be descendants of parent.

In the area where the new parent is visible around the top-level window of the application, the window manager can put anything it wants. This could include text, graphics, and small windows which perform certain functions when a button is clicked in them.

The window manager can decorate all top-level windows, but it will normally ignore windows that are mapped with their override_redirect attribute set, since no *Request events will be generated for them. The window manager may also decorate differently windows that have set the XA_WM_TRANSIENT_FOR property and apply its window layout policy to them. The window manager calls XGetTransientForHint() for each window to get this property.

By the way, it is impossible (except by luck) for the window manager to match the colors of the decoration to the colors of the window it is decorating. A window manager cannot find out what colors a window uses for its border or background because these window ...