src/Debug/Output/Html.php
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, $matches[1]);
    }
protected function visualWhiteSpaceCallback($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]);
    }
Adds whitespace markup

@param array $matches passed from preg_replace_callback

@return string