code: protected function addClasses(&$arrSource)
      {
          $countFiles = count($arrSource);
          foreach (array_keys($arrSource) as $k) {
              $arrSource[$k]['class'] = (($k == 0) ? ' first' : '') .
                  (($k == ($countFiles - 1)) ? ' last' : '') .
                  ((($k % 2) == 0) ? ' even' : ' odd');
          }
      }
docs: Attach first, last and even/odd classes to the given array.
  
  @param array $arrSource The array reference of the array to which the classes shall be added to.
  
  @return void