docs: private SimpleWindowState restoreWindowState() {
  		SimpleWindowState laststate = null;
  		final String statestr = preferences.get(prefnzPrefix+PREF_WINDOW_STATE, null);
  		if (logger.isDebugEnabled()) logger.debug("Restoring preference "+PREF_WINDOW_STATE+"=" + statestr);
  		if (statestr != null) {
  			SimpleWindowState state = null;
  			try {
  				state = SimpleWindowState.valueOf(statestr);
  			} catch (final IllegalArgumentException e) {	state = null; }
  			if (state != null) {
  				switch (state) {
  				case ICONFIED: this.setExtendedState(Frame.ICONIFIED);	break;
  				case NORMAL: this.setExtendedState(Frame.NORMAL); break;
  				case MAXIMIZED: this.setExtendedState(Frame.MAXIMIZED_BOTH); break;
  				default:
  					logger.error("Invalid window state (nothing will changed): " + statestr);
  				}
  			}
  			laststate = state;
  		}
  		return laststate;
  	}