public Cursor wrap(int sym) {
        root = new ObjectValue(names, sym, root);
        return root;
    }
Take the current top-level data object and make it a field in a
new ObjectValue with the given symbol id as field id; the new
ObjectValue will also become the new top-level data object.
vespajlib/src/main/java/com/yahoo/slime/Slime.java