docs: @SuppressWarnings("unchecked")
      private final void addBacktrackLocation(int usedAlternative) {
  	backtrackStack.push(new BacktrackLocation((Stack<Integer>) stateStack.clone(), actionStack.size(),
  		streamPosition, stepCounter, usedAlternative));
  	if (backtrackDepth > 0) {
  	    while (backtrackStack.size() > backtrackDepth) {
  		backtrackStack.remove(0);
  	    }
  	}
      }