pastebin - collaborative debugging

// tom morris - tommorris.org
// invoke with ob_start("callback"); ... ob_end_flush();
function callback($buffer) {
        $buffer = str_replace("<b>", "<strong>", $buffer);
        $buffer = str_replace("</b>", "</strong>", $buffer);
        $buffer = str_replace("<B>", "<strong>", $buffer);
        $buffer = str_replace("</B>", "</strong>", $buffer);
        $buffer = str_replace("<i>", "<em>", $buffer);
        $buffer = str_replace("</i>", "</em>", $buffer);
        $buffer = str_replace("<I>", "<em>", $buffer);
        $buffer = str_replace("</I>", "</em>", $buffer);
        $output = SmartyPants($buffer);
        // get the default mime type accepted by browser
        $defaultmime = mimeTypeChecker($_SERVER);
        // load into DOM and test
        $domtest = new DOMDocument('1.0');
        if (@$domtest->loadXML($output) == TRUE) {
          $mime = $defaultmime;
        } else {
          $mime = "text/html";
        }
        // return headers
        header('Content-Type: ' . $mime . ';charset=utf-8');
        header('Vary: Accept');
        return $output;
}

// uses mimeTypeChecker... thus included below. i didn't write
// this, cant remember where i took it from
function mimeTypeChecker($server) {
  $mime = 'text/html';
  if(strstr($server['HTTP_USER_AGENT'], 'W3C_Validator') ||
  strstr($server['HTTP_USER_AGENT'], 'WDG_SiteValidator') ||
  strstr($server['HTTP_USER_AGENT'], 'W3C-checklink') ||
  strstr($server['HTTP_USER_AGENT'], 'Web-Sniffer') ||
  strstr($server['HTTP_USER_AGENT'], 'FeedValidator') ||
  strstr($server['HTTP_USER_AGENT'], 'Poodle predictor') ||
  strstr($server['HTTP_USER_AGENT'], 'Leknor.com gzip tester')) {
        $mime = 'application/xhtml+xml';
  } else {
        if(stristr($server['HTTP_ACCEPT'], 'application/xhtml+xml')) {
                if(preg_match("/application\/xhtml\+xml;q=([01]|0\.\d{1,3}|1\.0)/i", $server['HTTP_ACCEPT'], $matches)) {
                        $xhtml_q = $matches[1];
                        if(preg_match("/text\/html;q=q=([01]|0\.\d{1,3}|1\.0)/i", $server['HTTP_ACCEPT'], $matches)) {
                                $html_q = $matches[1];
                                if((float)$xhtml_q >= (float)$html_q) {
                                        $mime = 'application/xhtml+xml';
                                }
                        }
          } else {
                  $mime = 'application/xhtml+xml';
          }
    }
  }
return $mime;
}