protected void adding(Item item) {
        Validator.ensureNotNull("A composite item child", item);
        Validator.ensure("Attempted to add a composite to itself", item != this);
        if (item instanceof CompositeItem) {
            ensureNotInSubtree((CompositeItem) item);
        }
        item.setParent(this);
    }
Sets the index name of all subitems of this
container-search/src/main/java/com/yahoo/prelude/query/CompositeItem.java