private void produce(RuleEvaluation e, Match match, List<Item> items, int offset) {
        if (replacing)
            insertMatch(e, match, items, offset);
        else
            e.addItems(items, getTermType());
    }
Returns the label of the condition this should take its value from, never null
container-search/src/main/java/com/yahoo/prelude/semantics/rule/ReferenceTermProduction.java