I originally raised this in vercel/next.js#65985 as I thought it was a Next.js/React issue, but it's a bug in json-viewer it seems.
Steps to reproduce
Serve a html document with the content of <html><body>Hello world</body</html>. Make sure to include a Content-Type: text/html; charset=UTF-8 header.
Expected
HTML to be rendered with the exact content as above.
Actual
The text node is wrapped in <text>:
<html><body><text>Hello world</text></body</html>