Vincent Lefevre <vincent@vinc17.net> writes:

> On 2019-05-26 18:17:55 -0400, Noam Postavsky wrote:
>> And about the highlighting of quoted text outside tags, we can just
>> disable fontification, while leaving the syntax code untouched:
> [...]
>
> I've applied it with a minor change against Emacs 26 (context lines
> for hunk #1 of sgml-mode.el are different), but the comments are
> no longer highlighted as comments.

Ah, I guess reusing the default font-lock-syntactic-face-function
doesn't really make sense after all.  So sgml-font-lock-syntactic-face
should be like this:

    (defun sgml-font-lock-syntactic-face (state)
      "`font-lock-syntactic-face-function' for `sgml-mode'."
      ;; Don't use string face outside of tags.
      (cond ((and (nth 9 state) (nth 3 state)) font-lock-string-face)
            ((nth 4 state) font-lock-comment-face)))