code: public function isAccompanyingPeriodValid(ExecutionContextInterface $context)
      {
          $r = $this->checkAccompanyingPeriodsAreNotCollapsing();
          
          if ($r !== true) {
              if ($r['result'] === self::ERROR_PERIODS_ARE_COLLAPSING) {
                  $context->addViolationAt('accompanyingPeriods',
                      'Two accompanying periods have days in commun',
                      array());
              }
              
              if ($r['result'] === self::ERROR_ADDIND_PERIOD_AFTER_AN_OPEN_PERIOD) {
                  $context->addViolationAt('accompanyingPeriods',
                      'A period is opened and a period is added after it',
                      array());
              }
          }
      }
docs: Validation callback that checks if the accompanying periods are valid
  
  This method add violation errors.