public void addRankFeatures(FeatureList features) {
        if (rankFeatures == null)
            rankFeatures = new LinkedHashSet<>();
        for (ReferenceNode feature : features) {
            rankFeatures.add(feature);
        }
    }
Adds the content of the given feature list to the internal list of rank features.

@param features The features to add.
config-model/src/main/java/com/yahoo/schema/RankProfile.java