code: function(point) {
          var resolution = this.getResolution();
          var x = ((point.x - this.featureDx) / resolution + this.left);
          var y = (this.top - point.y / resolution);
  
          if (this.inValidRange(x, y)) { 
              return x + "," + y;
          } else {
              return false;
          }
      }
docs: Method: getShortString
  
  Parameters:
  point - {<OpenLayers.Geometry.Point>}
  
  Returns:
  {String} or false if point is outside the valid range