docs: function(url, size, offset, calculateOffset) {
          this.url = url;
          this.size = size || {w: 20, h: 20};
          this.offset = offset || {x: -(this.size.w/2), y: -(this.size.h/2)};
          this.calculateOffset = calculateOffset;
  
          var id = OpenLayers.Util.createUniqueID("OL_Icon_");
          this.imageDiv = OpenLayers.Util.createAlphaImageDiv(id);
      }