21:56
<jmdyck>
https://html.spec.whatwg.org/#dom-navigator-appversion asserts that the result starts with "5.0 (", which can only be true if the "default User-Agent value" always begins with "Mozilla/5.0 (". That might be the case in practice, but the HTML spec and the Fetch spec don't appear to guarantee it. Does something else?
22:00
<jmdyck>
Oh, I see HTML has the comment Fetch doesn't actually require the value to start with "Mozilla/5.0 (".