code: function deepChild(root, path) {
    return path.reduce(function (node, index, x) {
      assert(index in node.children, 'child does not exist at the given deep index ' + path.join('.'));
      return node.children[index];
    }, root);
  }
docs: Retrieve a deep child via an input array `index` of indices to traverse.
  
  @param {Object} node  The virtual node to traverse.
  @param {Array:Number} path  The path to traverse.
  @return {Object}