With this patch, when any of the paired-bracket characters is followed
by `'' in html-mode, there is indeed no string face fontification on the
latter (and following characters).  The following function demonstrates
this:

(defun sgml-test-brackets ()
  "Test fontification of apostrophe preceded by paired-bracket character."
  (interactive)
  (let ((buf (get-buffer-create "*sgml-test*"))
	brackets results)
    (map-char-table
     (lambda (key value)
       (setq brackets (cons (list
			     (if (consp key)
				 (list (car key) (cdr key))
			       key)
			     value)
			    brackets)))
     (unicode-property-table-internal 'paired-bracket))
    (setq brackets (delete-dups (flatten-tree brackets)))
    (setq brackets (append brackets (list ?$ ?% ?& ?* ?+ ?/)))
    (while brackets
      (let ((char (string (pop brackets)))
	    (face "default"))
	(with-current-buffer buf
	  ;; (erase-buffer)
	  (fundamental-mode)
	  (insert (concat "<p>" char "'s</p>\n"))
	  (html-mode)
	  ;; (let ((val (get-text-property 5 'face)))
	  ;;   (when val (setq face (symbol-name val))))
	  ;; (push (concat char " : " face "\n") results)
	  )))
    ;; (with-current-buffer buf
    ;;   (newline)
    ;;   (while results
    ;; 	(insert (pop results))))
    (switch-to-buffer buf)))

I wanted to turn this function into a test, and that's what the
commented out lines are supposed to do.  But when I uncomment these
lines and call this function with the unpatched (i.e. current) version
of sgml-mode-syntax-table, it still shows default face for `'' with all
the paired-bracket characters.  Yet when I step through the function
with Ediff, I do see some cases with font-lock-string-face.  I don't
understand what's going on here.

Steve Berman