public void entering(String context) {
        if (context == null) return;
        if (matchReferences != null && matchReferences.contains(context)) {
            currentContext = context;
        }
    }
Advances currentItem to the next term item and returns thatItem.
If the current item before this call is the last item, this will
return (and set currentItem to) null.
container-search/src/main/java/com/yahoo/prelude/semantics/engine/RuleEvaluation.java