rem: scr->selected_windows = list_cons(wwin, scr->selected_windows);
add: if (!scr->selected_windows) scr->selected_windows = WMCreateBag(4); WMPutInBag(scr->selected_windows, wwin);
context: wSelectWindow(WWindow *wwin, Bool flag){    WScreen *scr = wwin->screen_ptr;    if (flag) {	wwin->flags.selected = 1;	XSetWindowBorder(dpy, wwin->frame->core->window, scr->white_pixel);	scr->selected_windows = list_cons(wwin, scr->selected_windows);    } else {	wwin->flags.selected = 0;	XSetWindowBorder(dpy, wwin->frame->core->window, 			 scr->frame_border_pixel);	scr->selected_windows = list_remove_elem(scr->selected_windows, wwin);    }}