My experiment to generate URL that begins with https:// and can be any HTML.
Use generator to make a link for any HTML content.
You can make a data URL for HTML:
const toURL = (html) => `data:text/html;base64,${btoa(html)}`
toURL(`<html><body>foo</body></html>`)
// => data:text/html;base64,PGh0bWw+PGJvZHk+Zm9vPC9ib2R5PjwvaHRtbD4=Surprisingly, <iframe> accepts such URL as src.
index.html just read the query string and open that in <iframe>.