code: protected function visualWhiteSpaceCallback($matches)
      {
          $strBr = $this->debug->getCfg('addBR') ? '<br />' : '';
          $search = array("\r","\n");
          $replace = array('<span class="ws_r"></span>','<span class="ws_n"></span>'.$strBr."\n");
          return \str_replace($search, $replace, $matches[1]);
      }
docs: Adds whitespace markup
  
  @param array $matches passed from preg_replace_callback
  
  @return string