/**
  * Adds route parameters for dynamic step navigation.
  * @param array $parameters Current route parameters.
  * @param FormFlow $flow The flow involved.
  * @param integer|null $stepNumber Number of the step the link will be generated for. If <code>null</code>, the <code>$flow</code>'s current step number will be used.
  * @return array Route parameters plus instance and step parameter.
  */
 public function addRouteParameters(array $parameters, FormFlow $flow, $stepNumber = null)
 {
     if ($stepNumber === null) {
         $stepNumber = $flow->getCurrentStepNumber();
     }
     $parameters[$flow->getDynamicStepNavigationInstanceParameter()] = $flow->getInstanceId();
     $parameters[$flow->getDynamicStepNavigationStepParameter()] = $stepNumber;
     return $parameters;
 }