public RankingExpression copy() {
        try {
            return new RankingExpression(name, root.toString());
        }
        catch (ParseException e) {
            throw new RuntimeException("Programming error: Could not parse serialized expression", e);
        }
    }
Returns a deep copy of this expression
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/RankingExpression.java