code: function placeKey(ka, v, k, pusher) {
    if (isObject(v)) {
      if (k in ka) {
        _keepAssigned(ka[k], v, pusher);
      } else {
        ka[k] = subKeepAssigned(ka.objs, k, pusher);
      }
    } else {
      if (k in ka) {
        ka[k].val = calcProp(ka, k);
      } else {
        defineProperty(ka, k, {
          get() { return U(findFirstProp(ka.objs, k)); },
          enumerable: true
        });
        //upward(v, ka[k]);
      }
    }
  }
docs: Place a key in the kept object.