private void lowerCase(WordItem word, IndexFacts.Session indexFacts) {
        if (shouldLowercase(word, indexFacts)) {
            word.setWord(toLowerCase(word.getWord()));
            word.setLowercased(true);
        }
    }
Traverse a query tree and lowercase terms based on decision made in subclasses.

@author Steinar Knutsen
container-search/src/main/java/com/yahoo/search/querytransform/LowercasingSearcher.java