code: function (bufferRatio) { // (Number) -> LatLngBounds
  		var sw = this._southWest,
  		    ne = this._northEast,
  		    heightBuffer = Math.abs(sw.lat - ne.lat) * bufferRatio,
  		    widthBuffer = Math.abs(sw.lng - ne.lng) * bufferRatio;
  
  		return new L.LatLngBounds(
  		        new L.LatLng(sw.lat - heightBuffer, sw.lng - widthBuffer),
  		        new L.LatLng(ne.lat + heightBuffer, ne.lng + widthBuffer));
  	}
docs: extend the bounds by a percentage