code: protected function visualWhiteSpace($str)
      {
          // display \r, \n, & \t
          $str = \preg_replace_callback('/(\r\n|\r|\n)/', array($this, 'visualWhiteSpaceCallback'), $str);
          $str = \preg_replace('#(<br />)?\n$#', '', $str);
          $str = \str_replace("\t", '<span class="ws_t">'."\t".'</span>', $str);
          return $str;
      }
docs: Add whitespace markup
  
  @param string $str string which to add whitespace html markup
  
  @return string