One example of code I can't understand

[Richard Stallman]

Here's more code from mm-util.el that I don't understand.
I don't know what this function is supposed to do
or how it works.


(defun mm-iso-8859-x-to-15-region (&optional b e)
  (if (fboundp 'char-charset)
      (let (charset item c inconvertible)
        (save-restriction
          (if e (narrow-to-region b e))
          (goto-char (point-min))
          (skip-chars-forward "\0-\177")
          (while (not (eobp))
            (cond
             ((not (setq item (assq (char-charset (setq c (char-after)))
                                    mm-iso-8859-x-to-15-table)))
              (forward-char))
             ((memq c (cdr (cdr item)))
              (setq inconvertible t)
              (forward-char))
             (t
              (insert-before-markers (prog1 (+ c (car (cdr item)))
                                       (delete-char 1)))))
            (skip-chars-forward "\0-\177")))
        (not inconvertible))))