protected function html($content, $depth = 0)
{
$r = str_pad('', ($depth - 1) * 3, '../');
$out = "<!DOCTYPE html>\n";
$out .= "<html>\n";
$out .= "<head>\n";
$out .= '<link rel="stylesheet" type="text/css" href="' . $r . 'html_report.css"/>';
$out .= "</head>\n";
$out .= "<body>\n";
$out .= $content;
$out .= "</body>\n";
$out .= '</html>';
return $out;
}