docs: function dependentKeysWillChange(obj, depKey, meta) {
      if (obj.isDestroying) {
        return;
      }
  
      if (meta && meta.hasDeps(depKey)) {
        var seen = WILL_SEEN;
        var top = !seen;
  
        if (top) {
          seen = WILL_SEEN = {};
        }
  
        iterDeps(propertyWillChange, obj, depKey, seen, meta);
  
        if (top) {
          WILL_SEEN = null;
        }
      }
    }