@Override
    public CompositeNode setChildren(List<ExpressionNode> newChildren) {
        if (newChildren.size() != 1)
            throw new IllegalArgumentException("Expected 1 child but got " + newChildren.size());
        return new EmbracedNode(newChildren.get(0));
    }
Returns the node enclosed by this
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/EmbracedNode.java