code: public function isDateConsistent(ExecutionContextInterface $context) {
          if ($this->isOpen()) {
              return;
          }
          
          if (! $this->isClosingAfterOpening()) {
              $context->addViolationAt('dateClosing', 
                  'The date of closing is before the date of opening',
                  array(), null);
          }
      }
docs: / VALIDATION function