docs: private final void trackBack() {
  	logger.trace("No valid action available. Perform back tracking...");
  	BacktrackLocation backtrackLocation = backtrackStack.peek();
  	streamPosition = backtrackLocation.getStreamPosition();
  	stepCounter = backtrackLocation.getStepCounter();
  	while (actionStack.size() > backtrackLocation.getActionStackSize()) {
  	    actionStack.remove(actionStack.size() - 1);
  	}
  	stateStack = backtrackLocation.getStateStack();
  	stepCounter--;
      }