docs: function(fields, destination, origin) {
        if ((!fields || fields === true) && this === origin && _.size(this.getTrackedModels()) > 1) {
          // only copy attributes that exist on object model when the form model is tracking all the properties
          // of that object model, but is also tracking other models as well.
          fields = _.keys(destination.attributes);
        }
        if (fields) {
          _.each(fields, function(field) {
            destination.set(field, this.__cloneVal(origin.get(field)));
          }, this);
        } else {
          destination.set(this.__cloneVal(origin.attributes));
        }
      }