To overcome the two problems here (client side loading the template and ending browser support) you could throw in php in the mix and have a wonderful solution for templating with bullet proof standards:
// XML
$xml_doc = new DOMDocument();
$xml_doc->load("file1.xml");
// XSL $xsl_doc = new DOMDocument(); $xsl_doc->load("file.xsl");
// Proc $proc = new XSLTProcessor(); $proc->importStylesheet($xsl_doc); $newdom = $proc->transformToDoc($xml_doc);
// Output print $newdom->saveXML();
XSLT lacks functionality? No problem, use php functions in xslt: https://www.php.net/manual/en/class.xsltprocessor.php