code: function() {
          if (!this._tileOrigin) {
              var extent = this.getMaxExtent();
              this._tileOrigin = new OpenLayers.LonLat(extent.left, extent.bottom);
          }
          return this._tileOrigin;
      }
docs: Method: getTileOrigin
  Determine the origin for aligning the grid of tiles.
  The origin will be derived from the layer's <maxExtent> property.
  
  Returns:
  {<OpenLayers.LonLat>} The tile origin.