@Override
    public Highlight clone() {
        try {
            Highlight clone = (Highlight) super.clone();

            clone.highlightItems = new LinkedHashMap<>();
            for (Map.Entry<String,AndItem> entry: highlightItems.entrySet()) {
                clone.highlightItems.put(entry.getKey(),(AndItem)entry.getValue().clone());
            }

            clone.highlightTerms = new LinkedHashMap<>();
            for (Map.Entry<String, List<String>> entry : highlightTerms.entrySet())
                clone.highlightTerms.put(entry.getKey(), new ArrayList<>(entry.getValue()));

            return clone;

        } catch (CloneNotSupportedException e) {
            throw new RuntimeException(e);
        }
    }
Returns the modifiable map of highlight items (never null)
container-search/src/main/java/com/yahoo/prelude/query/Highlight.java