docs: public void startNewKeyGroup(int keyGroupId) throws IOException {
  		if (isKeyGroupAlreadyStarted(keyGroupId)) {
  			throw new IOException("Key group " + keyGroupId + " already registered!");
  		}
  		keyGroupRangeOffsets.setKeyGroupOffset(keyGroupId, delegate.getPos());
  		currentKeyGroup = keyGroupId;
  	}