Wow! I like that. What happens with a 40x or 50x? I guess with 40x there's potential to bring the user to a sign in page if that's the problem, but if there'

Wow! I like that. What happens with a 40x or 50x? I guess with 40x there's potential to bring the user to a sign in page if that's the problem, but if there's a server error then it seems like the user may lose their form data and end up on a useless error page. Using 204 seems like a good default, though, because it means I can still use forms with JS turned off but I can choose for the site to be progressively enhanced by JS if I turn it on.