code: public function addFilterRule($objFilterRule)
      {
          if (!$this->objFilter) {
              $this->objFilter = $this->objMetaModel->getEmptyFilter();
          }
  
          $this->objFilter->addFilterRule($objFilterRule);
  
          return $this;
      }
docs: Add additional filter rules to the list on the fly.
  
  @param \MetaModels\Filter\IFilterRule $objFilterRule The filter rule to add.
  
  @return ItemList