code: public static List<String> getUnknownFeatures(HColumnDescriptor columnDescriptor) {
      List<String> unknownFeatures = new ArrayList<String>();
      for (Map.Entry<String, String> entry : columnDescriptor.getConfiguration().entrySet()) {
        String key = entry.getKey();
        if (!SUPPORTED_OPTION_KEYS.contains(key)
            && !IGNORED_OPTION_KEYS.contains(key)
            && !SUPPORTED_OPTION_VALUES.containsKey(key)) {
          unknownFeatures.add(key);
        }
      }
      return unknownFeatures;
    }
docs: Build a list of configuration keys that we don't know how to handle
  
  @param columnDescriptor a {@link org.apache.hadoop.hbase.HColumnDescriptor} object.
  @return a {@link java.util.List} object.