Check for COMMAND+SHIFT+Z

    switch(event.charCode)
    {
            case 90:      // Z
            case 122:    // z
                /* pre-Argo and on the mac then ignoreNextTextEvent */
                if (!Configuration.playerEnablesArgoFeatures && isMac) {
                    ignoreNextTextEvent = true;
                }

                if (event.shiftKey) {
                    redo();
                    event.preventDefault();

                } else {
                    undo();
                    event.preventDefault();
                }

                break;