protected boolean labelMatches(TermItem evaluationTerm, RuleEvaluation e) {
        String indexName = evaluationTerm.getIndexName();
        String label = getLabel();
        if (label == null)
            label = e.getCurrentLabel();
        if ("".equals(indexName) && label == null) return true;
        if ("default".equals(indexName) && label == null) return true;
        if (indexName.equals(label)) return true;
        if (e.getTraceLevel() >= 4)
            e.trace(4, "'" + this + "' does not match, label of " + e.currentItem() + " was required to be " + label);
        return false;
    }
Whether the label matches the current item, true if there is no current item
container-search/src/main/java/com/yahoo/prelude/semantics/rule/Condition.java