code: function() {
  			var focused = document.activeElement;
  			if(gui.DOMPlugin.contains(this.spirit.element, focused)) {
  				return this._focusselector(focused);	
  			}
  			return null;
  		}
docs: Focus is inside the spirit? Compute a fitting  CSS selector so that we
  may restore focus if and when the focused field gets replaced. This will
  in given case nuke the undo stack, but you can't both forget to scope
  your input fields (with an ID) and have a pleasent website, so please do.
  TODO: warning in debug mode when an ID is missing.
  @returns {string}