code: protected function format($html, $type, $level, array $options)
      {
          if ($options['compressed']) {
              return $html;
          }
  
          switch ($type) {
              case 'ul':
              case 'link':
                  $spacing = $level * 4;
                  break;
  
              case 'li':
                  $spacing = $level * 4 - 2;
                  break;
          }
  
          return str_repeat(' ', $spacing).$html."\n";
      }
docs: If $this->renderCompressed is on, this will apply the necessary
  spacing and line-breaking so that the particular thing being rendered
  makes up its part in a fully-rendered and spaced menu.
  
  @param string  $html    The html to render in an (un)formatted way
  @param string  $type    The type [ul,link,li] of thing being rendered
  @param integer $level
  @param array   $options
  
  @return string