code: function() {
          var filter = new OpenLayers.Filter.Spatial({
              type: OpenLayers.Filter.Spatial.BBOX,
              value: this.bounds,
              projection: this.layer.projection
          });
          if (this.layer.filter) {
              filter = new OpenLayers.Filter.Logical({
                  type: OpenLayers.Filter.Logical.AND,
                  filters: [this.layer.filter, filter]
              });
          }
          return filter;
      }
docs: Method: createFilter
  Creates a spatial BBOX filter. If the layer that this strategy belongs
  to has a filter property, this filter will be combined with the BBOX
  filter.
  
  Returns
  {<OpenLayers.Filter>} The filter object.