public void addMatchFeatures(FeatureList features) {
        if (matchFeatures == null)
            matchFeatures = new LinkedHashSet<>();
        for (ReferenceNode feature : features) {
            matchFeatures.add(feature);
        }
    }
Adds the content of the given feature list to the internal list of match features.
config-model/src/main/java/com/yahoo/schema/RankProfile.java