From: "NARUSE, Yui" <naruse@...>
Date: 2006-09-03T20:24:38+09:00
Subject: [ruby-dev:29438] Re: Time#rfc2822

成瀬です。

Tanaka Akira wrote:
>> UTC に偽装している不明の地方時という意味があるのかと思いました。どうし
>> てかというと、
> 
> ふむ。
> 
>>>   The 1 character military time zones were defined in a non-standard
>>>   way in [RFC822] and are therefore unpredictable in their meaning.
>>>   The original definitions of the military zones "A" through "I" are
>>>   equivalent to "+0100" through "+0900" respectively; "K", "L", and "M"
>>>   are equivalent to  "+1000", "+1100", and "+1200" respectively; "N"
>>>   through "Y" are equivalent to "-0100" through "-1200" respectively;
>>>   and "Z" is equivalent to "+0000".  However, because of the error in
>>>   [RFC822], they SHOULD all be considered equivalent to "-0000" unless
>>>   there is out-of-band information confirming their meaning.
>> これをみると -0000 は信頼に足る情報が存在しない場合の便宜的な印にすぎ
>> ないように思うからです。
> 
> これはエラー処理でしかたなくそうする、という話だと私は感じま
> す。
> 
> -0000 自体の意味は、+0000 の説明と並んでいる説明が基本的な意
> 味だと私は思っています。

知らなかったのですが、RFC3339 なんてあるのですね。
で、RFC3339に同旨と思われる記述がありました。

> 4.3. Unknown Local Offset Convention
> 
>    If the time in UTC is known, but the offset to local time is unknown,
>    this can be represented with an offset of "-00:00".  This differs
>    semantically from an offset of "Z" or "+00:00", which imply that UTC
>    is the preferred reference point for the specified time.  RFC2822
>    [IMAIL-UPDATE] describes a similar convention for email.

というわけで、ある時刻の正確なUTC表記はわかるが、
地方時がわからない場合の記述なようです。


-- 
NARUSE, Yui  <naruse@airemix.com>
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