Remove arch-tags from all files, since these are no longer needed.

[bpt/emacs.git] / lisp / gnus / utf7.el

;;; utf7.el --- UTF-7 encoding/decoding for Emacs   -*-coding: iso-8859-1;-*-

;; Copyright (C) 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007,
;;   2008, 2009, 2010  Free Software Foundation, Inc.

;; Author: Jon K Hellan <hellan@acm.org>
;; Maintainer: bugs@gnus.org
;; Keywords: mail

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; UTF-7 - A Mail-Safe Transformation Format of Unicode - RFC 2152
;; This is a transformation format of Unicode that contains only 7-bit
;; ASCII octets and is intended to be readable by humans in the limiting
;; case that the document consists of characters from the US-ASCII
;; repertoire.
;; In short, runs of characters outside US-ASCII are encoded as base64
;; inside delimiters.
;; A variation of UTF-7 is specified in IMAP 4rev1 (RFC 2060) as the way
;; to represent characters outside US-ASCII in mailbox names in IMAP.
;; This library supports both variants, but the IMAP variation was the
;; reason I wrote it.
;; The routines convert UTF-7 -> UTF-16 (16 bit encoding of Unicode)
;; -> current character set, and vice versa.
;; However, until Emacs supports Unicode, the only Emacs character set
;; supported here is ISO-8859.1, which can trivially be converted to/from
;; Unicode.
;; When decoding results in a character outside the Emacs character set,
;; an error is thrown.  It is up to the application to recover.

;; UTF-7 should be done by providing a coding system.  Mule-UCS does
;; already, but I don't know if it does the IMAP version and it's not
;; clear whether that should really be a coding system.  The UTF-16
;; part of the conversion can be done with coding systems available
;; with Mule-UCS or some versions of Emacs.  Unfortunately these were
;; done wrongly (regarding handling of byte-order marks and how the
;; variants were named), so we don't have a consistent name for the
;; necessary coding system.  The code below doesn't seem to DTRT
;; generally.  E.g.:
;;