code: private function getGridClass() {
          $class = [];
          foreach($this->grid as $grid){
              if(!isset($grid['type']) || !isset($grid['size'])){
                  throw new InvalidConfigException(get_called_class() . ' must have type and size.');
              }
              if(!isset($grid['positiontype']))
                  $class[] = $grid['type'].$grid['size'];
              else
                  $class[] = $grid['type'].$grid['positiontype'].'-'.$grid['size'];            
          }
          return implode(' ',$class);
      }
docs: Generate Grid Class for Div element
  @return string Html Class Value