RFC 1843 (rfc1843) - Page 3 of 5
HZ - A Data Format for Exchanging Files of Arbitrarily Mixed Chinese and ASCII characters
Alternative Format: Original Text Document
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