gistfile1.el

(defun pretty-print1 ()
  (interactive)
  (beginning-of-buffer) ;; Retourne au debut du buffer
  (setq level 0)
  (while (search-forward-regexp "<[^\!]" nil t)
    (let ((is-ending-tag (is-ending-tag)))
      (if is-ending-tag
          (setq level (- level 1)))
      (indent-before-tag level)
      (if (not is-ending-tag)
        (setq level (+ level 1))))))

(defun indent-before-tag (indent)
  (backward-char 2)
  (if (not (is-at-beginning-of-line))
      (insert-char ?\n 1))
  (insert-char ?\t indent)
  (forward-char 2))

(defun is-at-beginning-of-line ()
  (setq result t)
  (let ((start-point (point)))
    (while (not (bolp))
      (backward-char 1)
      (if (not (or
           (equal (following-char) ?\t)
           (equal (following-char) ? )))
          (setq result nil)))
    (goto-char start-point)
    result))

(defun is-ending-tag ()
  (equal (preceding-char) ?/))