docs: function(visible, force) {
  			if (this._zoomRulerVisible === visible && !force) { return; }
  			this._zoomRulerVisible = visible;
  			if (!this._zoomRuler) { return; }
  			var textView = this._textView;
  			if (visible) {
  				textView.addRuler(this._zoomRuler);
  			} else {
  				textView.removeRuler(this._zoomRuler);
  			}
  		}