// FIRST

  function send_header($contenttype='application/xhtml+xml') {
      $GLOBALS['now'] = gmdate('D, d M Y H:i:s') . ' GMT';
      header('Expires: ' . $GLOBALS['now']); // rfc2616 - Section 14.21
      header('Last-Modified: ' . $GLOBALS['now']); // Always modified
      //header("Cache-Control: post-check=0, pre-check=0", false);
      header('Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0'); // HTTP/1.1
      header('Pragma: no-cache'); // HTTP/1.0
      if($contenttype!='application/xhtml+xml'){
          header('Content-Type: '.$contenttype);
      }else{
          global $mime;
          $mime='text/html';
          if(stristr($_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';
              }
          }

          header('Content-Type: '.$mime.'; charset='.$GLOBALS['charset']);
          header('Vary: Accept');
      }
  }
// THEN


<?xml version="1.0" encoding="utf-8" ?>
<?xml-stylesheet href="./library/css/css.standard.php?token=f484ee372b9449927074c24967d47b18" type="text/css" media="all"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
         "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
      xml:lang="nb"
      lang="nb"
      dir="ltr">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
...


// BY:

  function page_start($meta=false,$js=false,$css=false,$other=false){
      global $mime;
      if($mime=='application/xhtml+xml'){
          echo '<?xml version="1.0" encoding="'.$GLOBALS['charset'].'" ?>'."\n";// IE Fix
          echo '<?xml-stylesheet href="./library/css/css.standard.php'.RHL_generate_common_url($_GET,'','&amp;').'" type="text/css" media="all"?>', "\n";
      }
      echo '<!DOCTYPE '.$GLOBALS['cfg']['pg']['doctype'].'>'."\n";
      echo '<html xmlns="'.$GLOBALS['cfg']['pg']['xmlns'].'"
      xml:lang="'.$GLOBALS['lang'][1].'"
      lang="'.$GLOBALS['lang'][1].'"
      dir="'.$GLOBALS['text_dir'].'">'."\n";
...

  }