private void addHighlightItem(String key, Item value) {
        AndItem item = highlightItems.get(key);
        if (item == null) {
            item = new AndItem();
            highlightItems.put(key, item);
        }
        item.addItem(value);
    }
The name of the property map which contains extra highlight terms
container-search/src/main/java/com/yahoo/prelude/query/Highlight.java