code: private function _validate($oElement) : bool
      {
          if (is_array($oElement->getConstraint())) {
  
              foreach ($oElement->getConstraint() as $oConstraint) {
  
                  if (!$oConstraint->validate($_POST[$oElement->getName()])) {
  
                      return false;
                  }
              }
          }
  
          return true;
      }
docs: if the element is valide or not (with the constraint)
  
  @access private
  @param  object $oElement element of formular
  @return boolean