Subject: bug#61375: HTML+ <input checked> not highlighted

From: Dan Jacobson <[email-masked]>
Date: Thu, 09 Feb 2023 15:54:50 +0800

emacs -Q /tmp/x.html
C-h m, see:
"HTML+ mode defined in ‘mhtml-mode.el’:"
click it, and at the top is
;; This file is part of GNU Emacs.

EZ> What is "HTML+ mode", please? is it part of Emacs?