code: function () {
          var maxExtent = null;
          
          if ( this.markers && (this.markers.length > 0)) {
              var maxExtent = new OpenLayers.Bounds();
              for(var i=0, len=this.markers.length; i<len; i++) {
                  var marker = this.markers[i];
                  maxExtent.extend(marker.lonlat);
              }
          }
  
          return maxExtent;
      }
docs: APIMethod: getDataExtent
  Calculates the max extent which includes all of the markers.
  
  Returns:
  {<OpenLayers.Bounds>}