private Number asNumber(String numberString) {
        try {
            if (!numberString.contains(".")) return Long.valueOf(numberString);
        }
        catch (NumberFormatException e) {
            return new BigInteger(numberString);
        }
        return Double.valueOf(numberString);
    }
Sets the number expression of this - a number or range following the syntax specified in the class javadoc
container-search/src/main/java/com/yahoo/prelude/query/IntItem.java