行中で最初に現れた括弧と対応する閉じ括弧を（薄く）ハイライトする（編集には未対応）

gistfile1.el

;;; 行中で最初に現れた括弧と対応する閉じ括弧を（薄く）ハイライトする
;;;   (jit-lock-register #'dehighlight-paren)
;;; で動くつもり

(defvar paren-face 'paren-face)
(make-face 'paren-face)
(set-face-foreground 'paren-face "grey90")

(defun dehighlight-paren-1 (pos)
  (add-text-properties pos (1+ pos)
                       `(font-lock-face ,paren-face
                         rear-nonsticky t)))

(defun dehighlight-paren-rl ()
  (save-excursion
    (let ((close (point)))
      (forward-char)
      (backward-sexp)
      (when (catch 'tag
              (while (not (bolp))
                (backward-char)
                (when (eq (syntax-class (syntax-after (point))) 4)
                  (throw 'tag nil)))
              t)
        (dehighlight-paren-1 (point))
        (dehighlight-paren-1 close)))))

(defun dehighlight-paren-lr ()
  (save-excursion
    (let ((open (point)))
      (forward-sexp)
      (backward-char)
      (dehighlight-paren-1 open)
      (dehighlight-paren-1 (point)))))

(defun dehighlight-paren (start end)
  (save-excursion
    (goto-char start)
    (while (< (point) end)
      (forward-char)
      (let ((mode 'open))
       (case (syntax-class (syntax-after (point)))
         ((4)
          (when (not (eq mode 'close))
            (dehighlight-paren-lr))
          (forward-line))
         ((5)
          (setq mode 'close)
          (dehighlight-paren-rl)))))))