RE: Common/Limited Use

[Shawn Steele <Shawn.Steele@microsoft.com>]

That's why a definition would've been good :)  

I'm not sure there's much point to add the information "now".  Either your app's stuck with some legacy restriction requiring code page support or you should be using Unicode.  So either some code page(s) you already know about on this list are important to you, or they aren't.  Whether we call them "common, limited, or obsolete" doesn't change that.

It might be good if http://www.iana.org/assignments/character-sets and http://www.iana.org/assignments/charset-reg/index.html were updated to include a note to the effect that UTF-8 or UTF-16 may be preferred in many cases, something like:

"Many character sets are limited in their scope and many others have inconsistent implementations between vendors.  To enable the broadest set of characters in a manner that is most consistent between vendors, implementers should consider using UTF-8 or UTF-16."

-Shawn

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http://blogs.msdn.com/shawnste


________________________________________
From: "Martin J. Dürst" [duerst@it.aoyama.ac.jp]
Sent: Wednesday, September 21, 2011 9:09 PM
To: Shawn Steele
Cc: Ira McDonald; ietf-charsets@mail.apps.ietf.org; Makoto Murata (eb2m-mrt@asahi-net.or.jp)
Subject: Re: Big5 / CP950

On 2011/09/22 3:05, Shawn Steele wrote:
> I saw the “one of…”, but they aren’t defined in the RFC?  Your spirit of Limited Use sounds about right for big5 though.

I agree.

For some more comments, please see below.

> Thanks,
> Shawn
>
> From: Ira McDonald [mailto:blueroofmusic@gmail.com]
> Sent: Wednesday, September 21, 2011 9:41 AM
> To: Shawn Steele; Ira McDonald
> Cc: "Martin J. Dürst"; ietf-charsets@mail.apps.ietf.org; Makoto Murata (eb2m-mrt@asahi-net.or.jp)
> Subject: Re: Big5 / CP950
>
> Hi Shawn,
>
> RFC 2978 section 5 'Charset Registration Template'
>
>       "Intended usage:
>
>       (One of COMMON, LIMITED USE or OBSOLETE)"
>
> The spirit of LIMITED USE has been to discourage the use
> of legacy charsets that are particularly problematic - Big5.
>
> Not sure if OBSOLETE has ever been used.

I haven't checked, but I guess these were not introduced when the
charset registry was created, but with a later update.

I assume the distinction between COMMON and LIMITED USE was originally
intended as some kind of advice to implementers: If it's COMMON, then
make sure it's supported, if it's LIMITED USE, you may not need it. But
I don't think that has ever really worked.


> Martin - searching for this made me realize that the
> plaintext IANA Charset Registry at
>
>    ftp://ftp.iana.org/assignments/character-sets
>
> contains 257 entries - they don't include the Intended
> Usage field.
>
> I suggest we work w/ IANA to change the plaintext
> registry.

Assuming somebody has lots of spare time, that would indeed be a good
idea. Assuming that everybody's time is rather limited, it may have to
wait. There are quite a few other things in the registry that might
benefit from clearing up, but the critical mass may not be reached yet.

> In most cases this data is long lost (if ever submitted)
> because the directory
>
>    ftp://ftp.iana.org/assignments/charset-reg
>
> contains only 55 entries.

Lots of stuff was taken from http://tools.ietf.org/html/rfc1345 (and
some other places). There's no need to keep that kind of information in
separate templates.

Regards,    Martin.

> Cheers,
> - Ira
>
> Ira McDonald (Musician / Software Architect)
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