@Override
    public CompositeNode setChildren(List<ExpressionNode> newChildren) {
        if (children.size() != newChildren.size())
            throw new IllegalArgumentException("Expected " + children.size() + " children but got " + newChildren.size());
        return new OperationNode(newChildren, operators);
    }
Returns true if this node has lower precedence than the parent
(even though by virtue of being a node it will be calculated before the parent).
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/OperationNode.java