docs: function(target) {
          target = OpenLayers.Util.applyDefaults(target, this.defaults);
          target.nodeTolerance = target.nodeTolerance || target.tolerance;
          target.vertexTolerance = target.vertexTolerance || target.tolerance;
          target.edgeTolerance = target.edgeTolerance || target.tolerance;
          this.targets.push(target);
      }