code: function (nestedChildNodes, transaction, context, selfDebugID) // 0 in production and for roots
    {
      if (nestedChildNodes == null) {
        return null;
      }
      var childInstances = {};
  
      if (process.env.NODE_ENV !== 'production') {
        traverseAllChildren(nestedChildNodes, function (childInsts, child, name) {
          return instantiateChild(childInsts, child, name, selfDebugID);
        }, childInstances);
      } else {
        traverseAllChildren(nestedChildNodes, instantiateChild, childInstances);
      }
      return childInstances;
    }
docs: Generates a "mount image" for each of the supplied children. In the case
  of `ReactDOMComponent`, a mount image is a string of markup.
  
  @param {?object} nestedChildNodes Nested child maps.
  @return {?object} A set of child instances.
  @internal