@Override
    public void setWeight(int weight) {
        super.setWeight(weight);
        for (Iterator<Item> i = getItemIterator(); i.hasNext();) {
            Item word = i.next();
            word.setWeight(weight);
        }
    }
Adds subitem. The word will have its index name set to the index name of
this phrase. If the item is a word, it will simply be added, if the item
is a phrase, each of the words of the phrase will be added.

@throws IllegalArgumentException if the given item is not a WordItem or PhraseItem
container-search/src/main/java/com/yahoo/prelude/query/PhraseItem.java