(defun my-multi-toggle ()
  (interactive)
  (set-buffer-multibyte (not enable-multibyte-characters)))
(global-set-key (kbd "C-~") 'my-multi-toggle)

(defun poff-zap ()
  "Get the byte offset of point - A prototye, tested minimally only with UTF-16LE"
  (interactive)

  (let ((linect (- (line-number-at-pos) 1)) ;; line count to point
        (choncl (- (point) (point-at-bol))) ;; characters to point on current line
        (chrpnl 0) ;; chars per newline
        (bytpch 0) ;; bytes per char
        (bytpnl 0) ;; bytes per newline
        (offset 0) ;; the byte offset
        (coding  (car (split-string (symbol-name buffer-file-coding-system) "-")))
        (format (cadr (split-string (symbol-name buffer-file-coding-system) "-"))))

    (case (coding-system-eol-type buffer-file-coding-system)
      ('0 (setq chrpnl 1)) ;; unix
      ('1 (setq chrpnl 2)) ;; dos
      ('2 (setq chrpnl 1)) ;; mac
      (t))

    (if (> chrpnl 0)
        (cond
        ((string= "utf" coding)
            (cond
            ((string= "8" format)
                (progn
                (setq bytpch -1)
                ;; need to do an actual byte count
                ;;   using a UTF-8 parser
                ;; ...plus a BOM check(?)
            ))
            ((or
             (string= "16" format)
             (string= "16le" format))
                (progn
                (setq bytpch 2)
                (if (= 2 chrpnl) (setq offset linect))
                (setq offset (+ offset (point)))
                (setq offset (* offset bytpch))
            ))
            (t)))
        (t)))

     (message (concat
      "poff-zap: " (number-to-string bytpch)  " bytes-per-charn"
      "          " (number-to-string chrpnl)  " chars-per-newlinern"
      "          " (number-to-string bytpnl)  " bytes-per-newlinern"
      "          " (number-to-string (point)) " point-emacsn"
      "          " (number-to-string offset)  " offset poff-zapn"
      "          " (symbol-name buffer-file-coding-system) ))
))
(global-set-key (kbd "C-#") 'poff-zap)

M-: (1- (position-bytes (point)))

(defun wh/byte-offset-at-point ()
  "Report the byte offset (0-indexed) in the file
corresponding to the position of point."
  (interactive)
  (message "byte offset: %d" (1- (position-bytes (point)))))