public static Map<String, VersionRange> defaultFeatureMap(boolean enableUnstable) {
        Map<String, VersionRange> features = new HashMap<>(1);
        features.put(MetadataVersion.FEATURE_NAME, VersionRange.of(
                MetadataVersion.MINIMUM_KRAFT_VERSION.featureLevel(),
                enableUnstable ?
                    MetadataVersion.latestTesting().featureLevel() :
                    MetadataVersion.latestProduction().featureLevel()));
        for (Features feature : Features.PRODUCTION_FEATURES) {
            short maxVersion = enableUnstable ? feature.latestTesting() : feature.latestProduction();
            if (maxVersion > 0) {
                features.put(feature.featureName(), VersionRange.of(feature.minimumProduction(), maxVersion));
            }
        }
        features.put(AutoMQVersion.FEATURE_NAME, VersionRange.of(AutoMQVersion.V0.featureLevel(), AutoMQVersion.LATEST.featureLevel()));
        return features;
    }
A holder class of the local node's supported feature flags as well as the quorum node IDs.
metadata/src/main/java/org/apache/kafka/controller/QuorumFeatures.java