A window manager may want to control the placement of subwindows. If SubstructureRedirectMask has been selected by a window manager on a parent window (usually a root window), a map request initiated by other clients on a child window is not performed, and the window manager is sent a MapRequest event. However, if the override-redirect flag on the child had been set to True (usually only on pop-up menus), the map request is performed.
A tiling window manager might decide to reposition and resize other clients' windows and then decide to map the window to its final location. A window manager that wants to provide decoration might reparent the child into a frame first. For further information, see "Override Redirect Flag" and "Window State Change Events". Only a single client at a time can select for SubstructureRedirectMask.
Similarly, a single client can select for ResizeRedirectMask on a parent window. Then, any attempt to resize the window by another client is suppressed, and the client receives a ResizeRequest event.
To map a given window, use XMapWindow().
To map and raise a window, use XMapRaised().
To map all subwindows for a specified window, use XMapSubwindows().