ietf-822
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Re: "7" encoding in headers

1993-03-05 13:17:10
To:  ietf-822(_at_)dimacs(_dot_)rutgers(_dot_)edu
Subject:  Re: "7" encoding in headers
Date:  Fri, 05 Mar 93 19:50:29 +0900

For text that doesn't contain many '='s, the "7" is so similar to the
"Q" encoding that it doesn't seem worth the effort to define both.

For non-MU text that *does* contain some '='s, *requiring* it to be
distorted and lengthened seems a bit unreasonable.  Of course, only
pieces of text that are safe in the context of the encoded-word can be
given a label of "7", but it seems like "7" would be desirable when
"B" and "Q" are not needed.

If the only objection to "7" is that it takes some effort to define
it, I will happily write the prose! :-)

My objection is that it complicates both the RFC 1342bis specification (thus
making it harder to understand and implement correctly) and the
implementation of a mail reader that supports header charsets, while the
added benefit is minimal.

I picked '=' because the character appears in most charsets (so e.g. it will
translate correctly into EBCDIC), and because it doesn't occur very often in
header text.  I don't think there will be enough instances of "non-MU text
that does contain some '='s" to make it worthwhile to define yet another
header encoding.

An implementation of "Q" is required to scan the text that it is about
to encode, and if it contains "?=" then this must be quoted since it
is the end-of-encoded-word marker.  Similarly, if the text contains
"<" and the encoded-word happens to be in a To: header, then the "<"
would have to be quoted to avoid clashes with addresses of the form
<user(_at_)foo(_dot_)com>.

My implementation of "Q" encoding just uses a per-character translate table.
The encoding for the Subject line uses a different translate table than the
encoding for the phrase before To.  The whole translation is done in one
pass.

(Which reminds me of the reason why some of the Japanese want to
mandate "B" for iso-2022-jp: "Q" is a pain to implement. 

And also, I suspect, because there's little point in using "Q" for Japanese
text, since it wouldn't be readable anyway.

Keith


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