Your browser (if you're using one of the "usual ones") doesn't really do much with the response's status code if it doesn't match a few specific ones for redirecting/caching/protocol shenanigans.
Anything in the 4XX range is going to be treated as just a regular ol' response, just like 404. (You could serve an entire site with all responses set to status=404, and be fine... other than probably never getting any cache hits) If you don't include a body in the response, the browser might sub in it's own error page, but it will just communicate that the user agent made a bad request.
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Your browser (if you're using one of the "usual ones") doesn't really do much with the response's status code if it doesn't match a few specific ones for redirecting/caching/protocol shenanigans.
Anything in the 4XX range is going to be treated as just a regular ol' response, just like 404. (You could serve an entire site with all responses set to status=404, and be fine... other than probably never getting any cache hits) If you don't include a body in the response, the browser might sub in it's own error page, but it will just communicate that the user agent made a bad request.