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+Network Working Group                                             F. Lee
+Request for Comments: 1843                           Stanford University
+Category: Informational                                      August 1995
+
+
+               HZ - A Data Format for Exchanging Files of
+             Arbitrarily Mixed Chinese and ASCII characters
+
+Status of this Memo
+
+   This memo provides information for the Internet community.  This memo
+   does not specify an Internet standard of any kind.  Distribution of
+   this memo is unlimited.
+
+Abstract
+
+   The content of this memo is identical to an article of the same title
+   written by the author on September 4, 1989.  In this memo, GB stands
+   for GB2312-80.  Note that the title is kept only for historical
+   reasons.  HZ has been widely used for purposes other than "file
+   exchange".
+
+1. Introduction
+
+   Most existing computer systems which can handle a text file of
+   arbitrarily mixed Chinese and ASCII characters use 8-bit codes.  To
+   exchange such text files through electronic mail on ASCII computer
+   systems, it is necessary to encode them in a 7-bit format.  A generic
+   binary to ASCII encoder is not sufficient, because there is currently
+   no universal standard for such 8-bit codes. For example, CCDOS and
+   Macintosh's Chinese OS use different internal codes.  Fortunately,
+   there is a PRC national standard, GuoBiao (GB), for the encoding of
+   Chinese characters, and Chinese characters encoded in the above
+   systems can be easily converted to GB by a simple formula. (* The ROC
+   standard BIG-5 is outside the scope of this article.)
+
+   HZ is a 7-bit data format proposed for arbitrarily mixed GB and ASCII
+   text file exchange.  HZ is also intended for the design of terminal
+   emulators that display and edit mixed Chinese and ASCII text files in
+   real time.
+
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+Lee                          Informational                      [Page 1]
+
+RFC 1843        HZ - A Data Format for Exchanging Files      August 1995
+
+
+2. Specification
+
+   The format of HZ is described in the following.
+
+   Without loss of generality, we assume that all Chinese characters
+   (HanZi) have already been encoded in GB.  A GB (GB1 and GB2) code is
+   a two byte code, where the first byte is in the range $21-$77
+   (hexadecimal), and the second byte is in the range $21-$7E.
+
+   A graphical ASCII character is a byte in the range $21-$7E. A non-
+   graphical ASCII character is a byte in the range $0-$20 or of the
+   value $7F.
+
+   Since the range of a graphical ASCII character overlaps that of a GB
+   byte, a byte in the range $21-$7E is interpreted according to the
+   mode it is in.  There are two modes, namely ASCII mode and GB mode.
+
+   By convention, a non-graphical ASCII character should only appear in
+   ASCII mode.
+
+   The default mode is ASCII mode.
+
+   In ASCII mode, a byte is interpreted as an ASCII character, unless a
+   '~' is encountered. The character '~' is an escape character. By
+   convention, it must be immediately followed ONLY by '~', '{' or '\n'
+   (<LF>), with the following special meaning.
+
+   o The escape sequence '~~' is interpreted as a '~'.
+   o The escape-to-GB sequence '~{' switches the mode from ASCII to
+     GB.
+   o The escape sequence '~\n' is a line-continuation marker to be
+     consumed with no output produced.
+
+   In GB mode, characters are interpreted two bytes at a time as (pure)
+   GB codes until the escape-from-GB code '~}' is read. This code
+   switches the mode from GB back to ASCII.  (Note that the escape-
+   from-GB code '~}' ($7E7D) is outside the defined GB range.)
+
+   The decoding process is clear from the above description.
+
+   The encoding process is straightforward. Note that an (ASCII) '~' is
+   always encoded as '~~'. A sequence of GB codes is enclosed in '~{'
+   and '~}'.
+
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+Lee                          Informational                      [Page 2]
+
+RFC 1843        HZ - A Data Format for Exchanging Files      August 1995
+
+
+3. Remarks & Recommendations
+
+   We choose to encode any ASCII character except '~' as it is, rather
+   than as a two byte code, and we choose ASCII as the default mode for
+   the following reasons. The computer systems we use is ASCII based.  A
+   HZ file containing pure ASCII characters (i.e. no Chinese characters)
+   except '~' is precisely a pure ASCII file. In general, the English
+   (ASCII) portion of a HZ file is directly readable.
+
+   The escape character '~' is chosen not only because it is commonly
+   used in the ASCII world, but also because '~' ($7E) is outside the
+   defined range ($21-$77) of the first byte of a GB code.
+
+   In ASCII mode, other potential escape sequences, i.e., two byte
+   sequences beginning with '~' (other than '~~', '~{', '~\n') are
+   currently invalid HZ sequences. Hence, they can be used for future
+   extension of HZ with total upward compatibility.
+
+   The line-continuation marker '~\n' is useful if one wants to encode
+   long lines in the original text into short lines in this data format
+   without introducing extra newline characters in the decoding process.
+
+   There is no limit on the length of a line. In fact, the whole file
+   could be one long line or even contain no newline characters. Any
+   DECODER of this HZ data format should not and has no need to operate
+   on the concept of a line.
+
+   It is easy to write encoders and decoders for HZ. An encoder or
+   decoder needs to lookahead at most one character in the input data
+   stream.
+
+   Given the current mode, it is also possible and easy to decode a HZ
+   data stream by scanning backward. One of the implication is that
+   "backspaces" can be handled correctly by a terminal emulator.
+
+   To facilitate the effective use of programs supporting line/page
+   skips such as "more" on UNIX with a terminal emulator understanding
+   the HZ format, it is RECOMMENDED that the ENCODER (which outputs in
+   HZ) sets a maximum line size of less than 80 characters.  Since '\n'
+   is an ASCII character, the syntax of HZ then automatically implies
+   that GB codes appearing at the end of a line must be terminated with
+   the escape-from-GB code '~}', and the line-continuation marker '~\n'
+   should be inserted appropriately. The price to paid is that the
+   encoded file size is slightly larger.
+
+   It is important to understand the following distinction.  Note that
+   the above recommendation does NOT change the HZ format.  It is simply
+   an encoding "style" which follows the syntax of HZ. Note that this
+
+
+
+Lee                          Informational                      [Page 3]
+
+RFC 1843        HZ - A Data Format for Exchanging Files      August 1995
+
+
+   "style" is not built into HZ. It is an additional convention built
+   "on top of" HZ.  Other applications may require different "styles",
+   but the same basic HZ DECODER will always work. The essence of HZ is
+   to provide such a flexible basic data format for files of arbitrarily
+   mixed Chinese and ASCII characters.
+
+4. Examples
+
+   To illustrate the "stylistic" issue of HZ encoding, we give the
+   following four examples of encoded text, which should produce the
+   same decoded output. (The recommendation in the last section refers
+   to Example 2.)
+
+   Example 1:  (Suppose there is no line size limit.)
+   This sentence is in ASCII.
+   The next sentence is in GB.~{<:Ky2;S{#,NpJ)l6HK!#~}Bye.
+
+   Example 2:  (Suppose the maximum line size is 42.)
+   This sentence is in ASCII.
+   The next sentence is in GB.~{<:Ky2;S{#,~}~
+   ~{NpJ)l6HK!#~}Bye.
+
+   Example 3: (Suppose a new line is started whenever there is a mode
+              switch.)
+   This sentence is in ASCII.
+   The next sentence is in GB.~
+   ~{<:Ky2;S{#,NpJ)l6HK!#~}~
+   Bye.
+
+Acknowledgement
+
+   Edmund Lai was the first one who brought my attention to this topic.
+   Discussions with Ed, Tin-Fook Ngai, Yagui Wei and Ricky Yeung were
+   very helpful in shaping the ideas in this article. Thanks to Tin-Fook
+   for his careful review of the draft and numerous interesting
+   suggestions.
+
+References
+
+   [1] Fung Fung Lee, "HZ - A Data Format for Exchanging Files of
+       Arbitrarily Mixed Chinese and ASCII Characters," September 4,
+       1989.
+       As part of //ftp.ifcss.org/software/unix/convert/HZ-2.0.tar.gz
+
+Security Considerations
+
+   Security issues are not addressed in this memo.
+
+
+
+
+Lee                          Informational                      [Page 4]
+
+RFC 1843        HZ - A Data Format for Exchanging Files      August 1995
+
+
+Author's Address
+
+   Fung Fung Lee
+   Computer Systems Laboratory
+   Stanford University
+   Stanford, CA 94309
+
+   Phone: +1 415 723 1450
+   EMail: lee@csl.stanford.edu
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+Lee                          Informational                      [Page 5]
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