Ruby RB is no error?

According to
https://html.spec.whatwg.org/multipage/obsolete.html#non-conforming-features
<rb>, <big>, <tt> are obsolete, non-conforming.
But I get errors only for <big> and <tt>, not for <rb>.

Example:

<!DOCTYPE html>
<html lang=''> <title>rb</title>
<p><big>BIG</big> <tt>TT</tt>
<ruby><rb>RB<rt>RT</ruby></html>

Received on Thursday, 1 September 2022 16:48:43 UTC