code: function(obj, visitor, context, traversalStrategy) {
        traversalStrategy = traversalStrategy || this._traversalStrategy;
        walkImpl(obj, traversalStrategy, null, visitor, context);
      }
docs: Recursively traverses `obj` in a depth-first fashion, invoking the `visitor` function for each object only after traversing its children. `traversalStrategy` is intended for internal callers, and is not part of the public API.