docs: function(mapBounds) {
          if(!mapBounds) {
              mapBounds = this.getMapBounds();
          }
          var invalid = !this.bounds || !this.bounds.containsBounds(mapBounds);
          if(!invalid && this.resFactor) {
              var ratio = this.resolution / this.layer.map.getResolution();
              invalid = (ratio >= this.resFactor || ratio <= (1 / this.resFactor));
          }
          return invalid;
      }