Re-parenting window manager: Meaning (information, definition, explanation, facts)

In the X Window System, every window has a parent window. This may either be the X root window, or another window. A window manager is said to be reparenting if it attempts to become the (indirect) parent of all windows that request to become visible and are parented by the X root window. This allows the window manager to decorate the windows with window frames and title bars as well as allows advanced control over the windows' operation required, for example, by virtual window managers.

In practice, a reparenting window manager registers with the X server to be notified when a window parented by the root X window attempts to become visible (mapping). When such an event is generated, the window manager creates a frame window, and in most cases also a title bar window. The frame window then becomes the parent of both the main window and the title bar window. Other forms of decoration, such as buttons, window title, etc., may also be created; these would normally be parented by the title bar window.

All modern window managers are re-parenting, although earlier window managers, such as the uwm window manager, were not.