code: 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));
        }
      }
docs: Copies fields from one backbone model to another. Is useful during a pull or push to/from Object models. The values will
  be deep cloned from the origin to the destination.
  @param [fields] {Array} a string of attribute names on the origin model that will be copied. Leave null if all attributes
  are to be copied
  @param destination {Backbone.Model} the backbone model that will have values copied into
  @param origin {Backbone.Model} the backbone model that will be used to grab values.
  @private
  @method __copyFields