add: panel->callbacks.prepareForClose = prepareForClose;
context: InitAppearance(WMScreen *scr, WMWindow *win){    _Panel *panel;    panel = wmalloc(sizeof(_Panel));    memset(panel, 0, sizeof(_Panel));        panel->sectionName = _("Appearance Preferences");    panel->win = win;    panel->callbacks.createWidgets = createPanel;    panel->callbacks.updateDomain = storeData;    AddSection(panel, ICON_FILE);    return panel;}