code: private static void checkKey(String key) throws IllegalArgumentException {
  		if(key.endsWith(VALIDATED_SUFFIX)) throw new IllegalArgumentException("Key may not end with "+VALIDATED_SUFFIX+": "+key);
  		if(key.endsWith(MODIFIED_SUFFIX)) throw new IllegalArgumentException("Key may not end with "+MODIFIED_SUFFIX+": "+key);
  	}
docs: Makes sure the key is allowed, throws <code>IllegalArgumentException</code> when not allowed.