docs: private static void threadSafeAddRelation(GrammaticalRelation relation) {
      valuesLock.writeLock().lock();
      try { // try-finally structure taken from Javadoc code sample for ReentrantReadWriteLock
        synchronizedValues.add(relation);
        shortNameToGRel.put(relation.toString(), relation);
      } finally {
        valuesLock.writeLock().unlock();
      }
    }