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[4] [[RFC 822メッセージ]]における[DFN[[RUBY[行][ぎょう][line]]]]は、
[CODE[CRLF]]
で区切られた部分です。

* 行 (MIME)

[5] 
[[MIME]]
では、
[CODE[text/*]],
[CODE[message/*]],
[CODE[multipart/*]]
の定義に[[行]]の概念が深く関わっています。
詳しくは各項を参照。

[6] 
[[内容転送符号化]] [CODE[7bit]], [CODE[8bit]] は[[行]]単位のデータです。
[CODE[8bit]] は[[行]]によって構成されるというのが [CODE[binary]]
との最大の違いです。

[FIG(quote)[ [3] [[RFC 2046]] 2.10
>
   "Lines" are defined as sequences of octets separated by a CRLF
   sequences.  This is consistent with both RFC 821 and RFC 822.
   "Lines" only refers to a unit of data in a message, which may or may
   not correspond to something that is actually displayed by a user
   agent.

「行 lines」は CRLF 列で区切られたオクテットの列と定義します。
これは RFC 821, RFC 822 の両者と同じです。
「行」はメッセージ中のデータの単位のみを指します。
利用者代理者が実際に表示するものと対応していてもいなくても構いません。
]FIG]

* [CODE[Lines:]] ヘッダー (ネットニュース)

** 仕様書

[1] [CITE@en[RFC 5536 - Netnews Article Format]]
( ([TIME[2014-09-21 18:14:06 +09:00]] 版))
<http://tools.ietf.org/html/rfc5536#section-3.3>

** 歴史

[FIG(quote)[ [2] [[son-of-RFC1036]]           6.11. Lines

[PRE[
          The Lines header content indicates the number  of  lines  in
          the body of the article:
]PRE]

[PRE[
               Lines-content = 1*digit
]PRE]

The line count includes all body lines, including the signature if any, 
including empty lines (if any) at beginning  or
end  of  the body.  (The single empty separator line between
the headers and the body is not  part  of  the  body.)   The
"body"  here  is  the  body  as found in the posted article,
AFTER all transformations such as MIME encodings.

行数には全ての本体行を含めます。署名があればこれを含めますし、
本体の始めや終わりの空白行 (があればこれ) も含めます。
(頭と本体の間の空行区切りは本体の一部ではありません。)
ここで「本体」は投稿記事の本体であり、 MIME 符号化のような
全ての変形の''後''のものであります。

[PRE[
          Reading agents SHOULD not  rely  on  the  presence  of  this
          header, since it is optional (and some posting agents do not
          supply it).  They MUST not rely on it being  precise,  since
          it frequently is not.
]PRE]

[PRE[
               NOTE: The average line length in article bodies is
               surprisingly consistent at  about  40  characters,
               and  since  the  line count typically is used only
               for approximate judgements ("is this too  long  to
               read  quickly?"),  dividing  the byte count of the
               body by 40 gives an  estimate  of  the  body  line
               count that is adequate for normal use.  This esti-
               mate is NOT adequate if the  body  has  been  MIME
               encoded...  but neither is the Lines header, since
               at least one major relayer  will  supply  a  Lines
               header for an article that lacks one, and will not
               consider the possibility of  MIME  encodings  when
               computing the line count.
]PRE]

[PRE[
               NOTE:  It  would  be better to have a Content-Size
               header as part of MIME, so that body  parts  could
               have  their  own sizes, and so that the units used
               could be appropriate to the data type (line  count
               is  not a useful measure of the size of an encoded
               image, for example).  Doing this is preferable  to
               trying to fix Lines.
]PRE]

[PRE[
               UNRESOLVED ISSUE: Update on Content-Size?
]PRE]

[PRE[
          Relayers  SHOULD  discard this header if they find it neces-
          sary to re-encode the article in such a way that the  origi-
          nal Lines header would be rendered incorrect.
]PRE]

]FIG]

* メモ

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