public Integer addToken(String token, int weight) {
        if (token == null) throw new IllegalArgumentException("token must be a string");
        return addInternal(token, weight);
    }
Adds a weighted token.
If this token is already in the set, the maximum weight is kept.
The weight must be 1 or more; negative values (and zero) are not allowed.

@return the weight of the added token (might be the old value, if kept)
container-search/src/main/java/com/yahoo/prelude/query/WeightedSetItem.java