Mark the window as a transient window (such as a pull-down menu or dialog) working on behalf of master, the path name of another top-level window. An empty string clears the transient status. With no argument, return the path name of the current master, or an empty string. A transient window mirrors state changes in its master and may be decorated differently by the window manager; it is an error to make a window a transient of itself. wm_transient() is an alias of transient().