Window.setTransientFor

Dialog windows should be set transient for the main application window they were spawned from. This allows [window managers][gtk-X11-arch] to e.g. keep the dialog on top of the main window, or center the dialog over the main window. [gtk.dialog.Dialog.newWithButtons] and other convenience functions in GTK+ will sometimes call [gtk.window.Window.setTransientFor] on your behalf.

Passing null for parent unsets the current transient window.

On Wayland, this function can also be used to attach a new #GTK_WINDOW_POPUP to a #GTK_WINDOW_TOPLEVEL parent already mapped on screen so that the #GTK_WINDOW_POPUP will be created as a subsurface-based window #GDK_WINDOW_SUBSURFACE which can be positioned at will relatively to the #GTK_WINDOW_TOPLEVEL surface.

On Windows, this function puts the child window on top of the parent, much as the window manager would have done on X.