private void addImplicitMatchFeatures(List<FeatureList> list) {
        if (hiddenMatchFeatures == null)
            hiddenMatchFeatures = new LinkedHashSet<>();
        var current = getMatchFeatures();
        for (var features : list) {
            for (ReferenceNode feature : features) {
                if (! current.contains(feature)) {
                    hiddenMatchFeatures.add(feature);
                }
            }
        }
    }
Returns a read-only view of the match features to use in this profile. This is never null
config-model/src/main/java/com/yahoo/schema/RankProfile.java