perlpodspec - Plain Old Documentation: フォーマット仕様とメモ
この文書は、Pod マークアップ言語の詳細なメモです。 ほとんどの人にとっては、Pod の書き方を知るには perlpod だけを 読む必要がありますが、この文書は Pod のパースとレンダリングに関する 付随的な質問に答えているかも知れません。
この文書では、"must" / "must not", "should" / "should not", "may" は形式的な意味 (RFC 2119 参照) を持ちます: "X must do Y" は、もし X は Y していない場合、これは仕様に反しているので、 本当に修正されるべきということを意味します。 "X should do Y" は、推奨はしますが、もし適切な理由があるなら、 X が Y しないこともあることを意味します。 "X may do Y" は、単に X が自分の意志で Y できることを示しています (しかし、これは読者が 「そして、私はもし X が Y するなら すてきだ と思う」と、 「X が Y するかどうかは どうでもいい」という言外の意味を識別できるように するようにしています)。 (訳注: 原文がどの表現を用いているかは文末にかっこで示します。)
特に、「パーサは Y するべきです(should)」と書いた場合、 呼び出し元のアプリケーションが明示的に Y しない ように指定した場合、 Y しないかもしれません。 これはしばしば、「パーサはデフォルトでは Y するべきです(should)」と 表現されます。 これはパーサが(そのままの段落でタブを展開するといった)機能 Y を オフにするかどうかのオプションを提供することを要求している わけではありませんが、 このようなオプションが提供されている かもしれない ことを示しています。
Pod は他のファイル (典型的には Perl ソースファイル) に埋め込まれていますが、 Pod 以外のことは全く知らなくても Pod を書けます。
ファイルの 行 (line) は 0 個以上の改行でない文字で構成され、 改行かファイルの終わりで終端されます。
改行シーケンス (newline sequence) は普通プラットフォーム依存の 概念ですが、Pod パーサは CR (ASCII 13), LF (ASCII 10), CRLF (ASCII 13 の直後に ASCII 10) に加えて、その他の システム固有の意味ののどれでも認識するべきです(should)。 ファイルの最初の CR/CRLF/LF シーケンスを、ファイルの残りをパースするための 改行を識別するための基準として使ってもかまいません(may)。
空行 (blank line) は 0 個以上のスペース (ASCII 32) かタブ (ASCII 9) のみで 構成され、改行かファイルの終わりで終端されます。 非空行 (non-blank line) はスペースとタブ以外の文字 1 個以上を含みます (そして改行かファイルの終わりで終端されます)。
(注意: 古い Pod パーサの多くはスペースとタブで構成される行を 受け付けず、改行を空行として扱います。 これらのパーサは 何の文字も含まれていない 行だけを空行として 扱います。)
空白 (whitespace) は、この文書ではスペース、タブ、改行シーケンスを 総称する用語です。 (それ自体、この用語は普通リテラルな空白を参照します。 That is, sequences of whitespace characters in Pod source, as opposed to "E<32>", which is a formatting code that denotes a whitespace character.) (TBT)
Pod パーサ (Pod parser) は Pod をパースするためのモジュールです (これはコールバックを呼び出すかパース木を構築するか直接フォーマットするかに 関わりません)。 Pod フォーマッタ (Pod formatter) (または Pod トランスレータ (Pod translator)) は Pod を他の形式 (HTML, プレーンテキスト、Tex, PostScript, RTF) に変換するモジュールかプログラムです。 Pod プロセッサ (Pod processor) はフォーマッタあるいはトランスレータか、 あるいは Pod に何かの処理(単語を数える、インデックスをスキャンする、など)を 行うプログラムかも知れません。
Pod の内容は Pod ブロック (Pod blocks) に含まれています。
一つの Pod ブロックは <m/\A=[a-zA-Z]/> にマッチングする行で開始し、
m/\A=cut/ にマッチングする次の行までか、もし
m/\A=cut/ 行がなければファイルの最後まで続きます。
Pod ブロックの内部は、Pod 段落(Pod paragraphs) です。 一つの Pod 段落は、1 以上の空行で分割された非空行のテキストで構成されます。
Pod 処理のために、Pod ブロックには 4 種類の段落があります:
コマンド段落 (command paragraph) (「指示子」(directive) とも呼ばれます)。
段落の最初の行は m/\A=[a-zA-Z]/ にマッチングしなければなりません(must)。
コマンド段落は典型的には以下のように 1 行です:
=head1 NOTES
=item *
しかし複数の (非空行の) 行にわたるかもしれません(may):
=for comment Hm, I wonder what it would look like if you tried to write a BNF for Pod from this.
=head3 Dr. Strangelove, or: How I Learned to Stop Worrying and Love the Bomb
一部の コマンド段落は、以下のように、内容 (つまり、
m/\A=[a-zA-Z]\S*\s*/ にマッチングする部分の後)にフォーマッティングコードを
許しています:
=head1 Did You Remember to C<use strict;>?
言い換えると、"head1" の Pod 処理ハンドラは、 apply the same processing to "Did You Remember to C<use strict;>?" that it would to an ordinary paragraph (i.e., formatting codes like "C<...>") are parsed and presumably formatted appropriately, and whitespace in the form of literal spaces and/or tabs is not significant. (TBT)
そのままの段落 (verbatim paragraph)。 この段落の最初の行はリテラルのスペースかタブでなければならず(must)、 この段落は "identifier" がコロン (":") で始まっていない限り "=begin identifier", ... "=end identifier" を内部に 含んではいけません(must not)。 つまり、もし段落がリテラルのスペースかタブで始まっているけれども、 内部に "=begin identifier", ... "=end identifier" 領域がある場合、 "identifier" がコロンで始まっていない限りデータ段落です。
空白はそのままの段落では 意味を持ちます (しかし、処理中に、タブは おそらく展開されます)。
通常の段落 (ordinary paragraph)。
A paragraph is an ordinary paragraph
if its first line matches neither m/\A=[a-zA-Z]/ nor
m/\A[ \t]/, and if it's not inside a "=begin identifier",
... "=end identifier" sequence unless "identifier" begins with
a colon (":").
(TBT)
データ段落 (data paragraph)。 これは "=begin identifier" ... "=end identifier" シーケンスの 内部で、"identifier" がリテラルのコロン (":") で 始まって いない ものです。 ある意味では、データ段落は Pod の一部ではありません (事実上「帯域外」です); なぜならほとんどの種類の Pod パーサが 想定していないからです; しかし、Pod パーサはこれのためのイベントを 呼び出したり、パース木に何らかの形で補完したり、あるいは少なくとも 単にその 周り をパースする必要があるからです。
例えば: 以下の段落を考えます:
# <- that's the 0th column
=head1 Foo
Stuff
$foo->bar
=cut
ここで、"=head1 Foo" と "=cut" は、それぞれ最初の行が m/\A=[a-zA-Z]/ に
マッチングするのでコマンド段落です。
"[space][space]$foo->bar" は、最初の行がリテラルの空白文字で始まる
(そして周りに "=begin"..."=end" 領域がない)のでそのままの段落です。
The "=begin identifier" ... "=end identifier" commands stop paragraphs that they surround from being parsed as ordinary or verbatim paragraphs, if identifier doesn't begin with a colon. これは About Data Paragraphs and "=begin/=end" Regions の章で 詳細に議論されています。 (TBT)
この章は perlpod/"Command Paragraph" での議論を補完して明確化することを 目的にしています。 現在認識されている Pod コマンドは以下の通りです:
このコマンドは、この段落の残りの文章が見出しであることを示します。 この文章にはフォーマッティングコードを含むことができます。 例:
=head1 Object Attributes
=head3 What B<Not> to Do!
このコマンドは、この段落から Pod ブロックが始まることを示します。 (すでに Pod ブロックの内部である場合は、このコマンドは何の効果も ありません。) もしこのコマンド段落の "=pod" の後に何らかの文章がある場合、 無視しなければなりません(must)。 例:
=pod
This is a plain Pod paragraph.
=pod This text is ignored.
This command indicates that this line is the end of this previously started Pod block. If there is any text after "=cut" on the line, it must be ignored. Examples: (TBT)
=cut
=cut The documentation ends here.
=cut
# This is the first line of program text.
sub foo { # This is the second.
It is an error to try to start a Pod block with a "=cut" command. In that case, the Pod processor must halt parsing of the input file, and must by default emit a warning. (TBT)
This command indicates that this is the start of a list/indent region. If there is any text following the "=over", it must consist of only a nonzero positive numeral. The semantics of this numeral is explained in the =over...=back 領域について section, further below. Formatting codes are not expanded. Examples: (TBT)
=over 3
=over 3.5
=over
This command indicates that an item in a list begins here. Formatting codes are processed. The semantics of the (optional) text in the remainder of this paragraph are explained in the =over...=back 領域について section, further below. Examples: (TBT)
=item
=item *
=item *
=item 14
=item 3.
=item C<< $thing->stuff(I<dodad>) >>
=item For transporting us beyond seas to be tried for pretended offenses
=item He is at this time transporting large armies of foreign mercenaries to complete the works of death, desolation and tyranny, already begun with circumstances of cruelty and perfidy scarcely paralleled in the most barbarous ages, and totally unworthy the head of a civilized nation.
This command indicates that this is the end of the region begun by the most recent "=over" command. It permits no text after the "=back" command. (TBT)
This marks the following paragraphs (until the matching "=end formatname") as being for some special kind of processing. Unless "formatname" begins with a colon, the contained non-command paragraphs are data paragraphs. But if "formatname" does begin with a colon, then non-command paragraphs are ordinary paragraphs or data paragraphs. This is discussed in detail in the section About Data Paragraphs and "=begin/=end" Regions. (TBT)
It is advised that formatnames match the regexp
m/\A:?[?a?zA?Z0?9_]+\z/. Everything following whitespace after the
formatname is a parameter that may be used by the formatter when dealing
with this region. This parameter must not be repeated in the "=end"
paragraph. Implementors should anticipate future expansion in the
semantics and syntax of the first parameter to "=begin"/"=end"/"=for".
(TBT)
This marks the end of the region opened by the matching "=begin formatname" region. If "formatname" is not the formatname of the most recent open "=begin formatname" region, then this is an error, and must generate an error message. This is discussed in detail in the section About Data Paragraphs and "=begin/=end" Regions. (TBT)
これは以下と同等です:
=begin formatname
text...
=end formatname
That is, it creates a region consisting of a single paragraph; that paragraph is to be treated as a normal paragraph if "formatname" begins with a ":"; if "formatname" doesn't begin with a colon, then "text..." will constitute a data paragraph. There is no way to use "=for formatname text..." to express "text..." as a verbatim paragraph. (TBT)
This command, which should occur early in the document (at least before any non-US-ASCII data!), declares that this document is encoded in the encoding encodingname, which must be an encoding name that Encode recognizes. (Encode's list of supported encodings, in Encode::Supported, is useful here.) If the Pod parser cannot decode the declared encoding, it should emit a warning and may abort parsing the document altogether. (TBT)
A document having more than one "=encoding" line should be considered an error. Pod processors may silently tolerate this if the not-first "=encoding" lines are just duplicates of the first one (e.g., if there's a "=encoding utf8" line, and later on another "=encoding utf8" line). But Pod processors should complain if there are contradictory "=encoding" lines in the same document (e.g., if there is a "=encoding utf8" early in the document and "=encoding big5" later). Pod processors that recognize BOMs may also complain if they see an "=encoding" line that contradicts the BOM (e.g., if a document with a UTF-16LE BOM has an "=encoding shiftjis" line). (TBT)
If a Pod processor sees any command other than the ones listed above (like "=head", or "=haed1", or "=stuff", or "=cuttlefish", or "=w123"), that processor must by default treat this as an error. It must not process the paragraph beginning with that command, must by default warn of this as an error, and may abort the parse. A Pod parser may allow a way for particular applications to add to the above list of known commands, and to stipulate, for each additional command, whether formatting codes should be processed. (TBT)
この仕様の将来のバージョンでは追加のコマンドが追加されるかもしれません。
(この文書の以前の草案と以前の perlpod では、フォーマッティングコードは 「内部シーケンス」(interior sequences) として参照されていて、 この用語は Pod パーサの文書や、Pod プロセッサのエラーメッセージに まだ残っていることに注意してください。)
フォーマッティングコードには二つの文法があります:
英大文字 (ちょうど US-ASCII [A-Z]) で始まり、次に "<"、その次に 任意の数の文字が続き、最初にマッチングする ">" で終わる フォーマッティングコード。 例:
That's what I<you> think!
What's C<dump()> for?
X<C<chmod> and C<unlink()> Under Different Operating Systems>
英大文字 (ちょうど US-ASCII [A-Z]) で始まり、2 個以上の "<"、 1 個以上の空白文字、任意の数の文字、1 個以上の空白文字が続き、 このフォーマッティングコードの最初にあった "<" と同じ数の ">" で 終わるフォーマッティングコード。 例:
That's what I<< you >> think!
C<<< open(X, ">>thing.dat") || die $! >>>
B<< $foo->bar(); >>
この文法では、"C<<<" の後ろと ">>" (やその他の文字) の前の空白文字は レンダリング されません 。 空白は認識せず、単にフォーマッティングコード自身の一部となります。 つまり、以下のものは全て同じ意味です:
C<thing>
C<< thing >>
C<< thing >>
C<<< thing >>>
C<<<<
thing
>>>>
および同様なものです。
最後に、複数山かっこ形式はネストしたフォーマッティングコードの解釈を 変更 しません; つまり、以下の四つの例は意味としては同じです:
B<example: C<$a E<lt>=E<gt> $b>>
B<example: C<< $a <=> $b >>>
B<example: C<< $a E<lt>=E<gt> $b >>>
B<<< example: C<< $a E<lt>=E<gt> $b >> >>>
Pod をパースするときに特にトリッキーな部分は、(ネストしているかもしれない!)
フォーマッティングコードを正しくパースすることです。
実装者は正しい実装の例として、Pod::Parsar の parse_text ルーチンの
コードを参考にするべきです。
I<text> -- イタリック文字perlpod/"Formatting Codes" にある簡潔な議論を参照してください。
B<text> -- ボールド文字perlpod/"Formatting Codes" にある簡潔な議論を参照してください。
C<code> -- コード文字perlpod/"Formatting Codes" にある簡潔な議論を参照してください。
F<filename> -- ファイル名用のスタイルperlpod/"Formatting Codes" にある簡潔な議論を参照してください。
X<topic name> -- インデックスエントリperlpod/"Formatting Codes" にある簡潔な議論を参照してください。
このコードは特殊で、ほとんどのフォーマッタはこのコードとその内容は 完全に捨てられます。 その他のフォーマッタは現在の文書のインデックス構築に使える 見えないコードとしてレンダリングされます。
Z<> -- a null (zero-effect) formatting codeperlpod/"Formatting Codes" で簡潔に議論されています。
このコードは特殊で、内容はなしであるべきです(should)。
つまり、プロセッサが Z<potatoes> を見ると異常とみなすかも
しれません(may)。
異常とみなすかどうかに関わらず、potatoes という文字は
無視されるべきです(should)。
L<name> -- ハイパーリンクこのコードの複雑な文法は perlpod/"Formatting Codes" で詳細に 議論されていて、実装の詳細は後述する About L<...> Codes に あります。 L<content> の内容のパースはトリッキーです。 特に、E<...> コードが解決される 前に 、 内容が URL のように見えるか、あるいは内容が "|" や "/" で 分割する必要があるか (右順序で!) などです。
E<escape> -- 文字エスケープperlpod/"Formatting Codes" と、 Pod プロセッサの実装に関するメモ にあるいくつかのポイントを 参照してください。 (TBT)
S<text> -- ノーブレークスペースを含む文字列このフォーマッティングコードは文法的には単純ですが、意味論的には複雑です。 これが意味することは、このコードの内容にあるそれぞれのスペースは ノーブレークスペースとして認識されるということです。
以下のものを考えます:
C<$x ? $y : $z>
S<C<$x ? $y : $z>>
どちらも "$x"、一つのスペース、"?"、一つのスペース、":"、一つのスペース、 "$z" からなる、固定幅 (コードスタイル) 文字列として認識されます。 違いは、S コードの付いている後者は、これらのスペースは「普通の」 スペースではなく、ノーブレークスペースであるということです。
If a Pod processor sees any formatting code other than the ones listed above (as in "N<...>", or "Q<...>", etc.), that processor must by default treat this as an error. A Pod parser may allow a way for particular applications to add to the above list of known formatting codes; a Pod parser might even allow a way to stipulate, for each additional command, whether it requires some form of special processing, as L<...> does. (TBT)
Future versions of this specification may add additional formatting codes. (TBT)
Historical note: A few older Pod processors would not see a ">" as closing a "C<" code, if the ">" was immediately preceded by a "-". This was so that this: (TBT)
C<$foo->bar>
would parse as equivalent to this: (TBT)
C<$foo-E<gt>bar>
instead of as equivalent to a "C" formatting code containing only "$foo-", and then a "bar>" outside the "C" formatting code. This problem has since been solved by the addition of syntaxes like this: (TBT)
C<< $foo->bar >>
Compliant parsers must not treat "->" as special. (TBT)
Formatting codes absolutely cannot span paragraphs. If a code is opened in one paragraph, and no closing code is found by the end of that paragraph, the Pod parser must close that formatting code, and should complain (as in "Unterminated I code in the paragraph starting at line 123: 'Time objects are not...'"). So these two paragraphs: (TBT)
I<I told you not to do this!
Don't make me say it again!>
...must not be parsed as two paragraphs in italics (with the I code starting in one paragraph and starting in another.) Instead, the first paragraph should generate a warning, but that aside, the above code must parse as if it were: (TBT)
I<I told you not to do this!>
Don't make me say it again!E<gt>
(In SGMLish jargon, all Pod commands are like block-level elements, whereas all Pod formatting codes are like inline-level elements.) (TBT)
The following is a long section of miscellaneous requirements and suggestions to do with Pod processing. (TBT)
Pod formatters should tolerate lines in verbatim blocks that are of any length, even if that means having to break them (possibly several times, for very long lines) to avoid text running off the side of the page. Pod formatters may warn of such line-breaking. Such warnings are particularly appropriate for lines are over 100 characters long, which are usually not intentional. (TBT)
Pod パーサは 3 種類のよく知られた改行 (CR, LF, CRLF) の 全て を 認識しなければなりません(must)。 perlport を参照してください。
Pod パーサは任意の長さの入力行を受け付けるべきです(should)。
Since Perl recognizes a Unicode Byte Order Mark at the start of files as signaling that the file is Unicode encoded as in UTF-16 (whether big-endian or little-endian) or UTF-8, Pod parsers should do the same. Otherwise, the character encoding should be understood as being UTF-8 if the first highbit byte sequence in the file seems valid as a UTF-8 sequence, or otherwise as Latin-1. (TBT)
Future versions of this specification may specify how Pod can accept other encodings. Presumably treatment of other encodings in Pod parsing would be as in XML parsing: whatever the encoding declared by a particular Pod file, content is to be stored in memory as Unicode characters. (TBT)
The well known Unicode Byte Order Marks are as follows: if the file begins with the two literal byte values 0xFE 0xFF, this is the BOM for big-endian UTF-16. If the file begins with the two literal byte value 0xFF 0xFE, this is the BOM for little-endian UTF-16. If the file begins with the three literal byte values 0xEF 0xBB 0xBF, this is the BOM for UTF-8. (TBT)
A naive but sufficient heuristic for testing the first highbit byte-sequence in a BOM-less file (whether in code or in Pod!), to see whether that sequence is valid as UTF-8 (RFC 2279) is to check whether that the first byte in the sequence is in the range 0xC0 - 0xFD and whether the next byte is in the range 0x80 - 0xBF. If so, the parser may conclude that this file is in UTF-8, and all highbit sequences in the file should be assumed to be UTF-8. Otherwise the parser should treat the file as being in Latin-1. In the unlikely circumstance that the first highbit sequence in a truly non-UTF-8 file happens to appear to be UTF-8, one can cater to our heuristic (as well as any more intelligent heuristic) by prefacing that line with a comment line containing a highbit sequence that is clearly not valid as UTF-8. A line consisting of simply "#", an e-acute, and any non-highbit byte, is sufficient to establish this file's encoding. (TBT)
この文書のエンコーディングに関する要求と提案は、非 ASCII プラットフォーム、 特に EBCDIC プラットフォームには適用されません。
Pod プロセッサは、"=for [label] [content...]" 段落を、 "=begin [label]" 段落、内容、"=end [label]" 段落と同じように 扱わなければなりません(must)。 (The parser may conflate these two constructs, or may leave them distinct, in the expectation that the formatter will nevertheless treat them the same.) (TBT)
Pod を、コメントが許されるフォーマット (つまり、ほぼ、プレーンテキスト以外の あらゆるフォーマット) にレンダリングするとき、 Pod フォーマッタは、自身の名前とバージョン番号、および Pod を 処理するときに使った全てのモジュールの名前とバージョン番号が識別できる コメントを挿入しなければなりません(must)。 最小限の例:
%% POD::Pod2PS v3.14159, using POD::Parser v1.92
<!-- Pod::HTML v3.14159, using POD::Parser v1.92 -->
{\doccomm generated by Pod::Tree::RTF 3.14159 using Pod::Tree 1.08}
.\" Pod::Man version 3.14159, using POD::Parser version 1.92
フォーマッタは、Pod フォーマッタプログラムのリリース日、フォーマッタの 作者への連絡アドレス、現在時刻、入力ファイル名、適用された フォーマットオプション、使われた Perl のバージョンといった 追加のコメントを挿入してもかまいません(may)。
Formatters may also choose to note errors/warnings as comments,
besides or instead of emitting them otherwise (as in messages to
STDERR, or dieing).
(TBT)
Pod parsers may emit warnings or error messages ("Unknown E code
E<zslig>!") to STDERR (whether through printing to STDERR, or
warning/carping, or dieing/croaking), but must allow
suppressing all such STDERR output, and instead allow an option for
reporting errors/warnings
in some other way, whether by triggering a callback, or noting errors
in some attribute of the document object, or some similarly unobtrusive
mechanism -- or even by appending a "Pod Errors" section to the end of
the parsed form of the document.
(TBT)
極端に異常な文書の場合は、Pod パーサはパースを中断してもかまいません(may)。
それでも、die/croak の使用は避けます; 可能なら、パーサは単に
入力ファイルを閉じて、メモリにある文書(の一部)の末尾に
"*** Formatting Aborted ***" のような文章を追加できます(may)。
In paragraphs where formatting codes (like E<...>, B<...>) are understood (i.e., not verbatim paragraphs, but including ordinary paragraphs, and command paragraphs that produce renderable text, like "=head1"), literal whitespace should generally be considered "insignificant", in that one literal space has the same meaning as any (nonzero) number of literal spaces, literal newlines, and literal tabs (as long as this produces no blank lines, since those would terminate the paragraph). Pod parsers should compact literal whitespace in each processed paragraph, but may provide an option for overriding this (since some processing tasks do not require it), or may follow additional special rules (for example, specially treating period-space-space or period-newline sequences). (TBT)
Pod parsers should not, by default, try to coerce apostrophe (') and quote (") into smart quotes (little 9's, 66's, 99's, etc), nor try to turn backtick (`) into anything else but a single backtick character (distinct from an open quote character!), nor "--" into anything but two minus signs. They must never do any of those things to text in C<...> formatting codes, and never ever to text in verbatim paragraphs. (TBT)
When rendering Pod to a format that has two kinds of hyphens (-), one that's a non-breaking hyphen, and another that's a breakable hyphen (as in "object-oriented", which can be split across lines as "object-", newline, "oriented"), フォーマッタは一般的に "-" を改行なしのハイフンに変換することが 推奨されますが、これらの一部を改行するハイフンに変換するための 発見的手法を適用してもかまいません(may)。 (TBT)
Pod フォーマッタは、Perl コードの単語が行をまたがないように 合理的な努力を行うべきです(should)。 For example, "Foo::Bar" in some formatting systems is seen as eligible for being broken across lines as "Foo::" newline "Bar" or even "Foo::-" newline "Bar". This should be avoided where possible, either by disabling all line-breaking in mid-word, or by wrapping particular words with internal punctuation in "don't break this across lines" codes (which in some formats may not be a single code, but might be a matter of inserting non-breaking zero-width spaces between every pair of characters in a word.) (TBT)
Pod パーサは、デフォルトでは、フォーマッタやその他のプロセッサに 渡す前に、そのままの段落のタブを展開するべきです(should)。 パーサはこれを上書きするオプションを許してもかまいません(may)。
Pod パーサは、デフォルトでは、通常の段落とそのままの段落の末尾の 改行を、フォーマッタに渡す前に削除するべきです(should)。 For example, while the paragraph you're reading now could be considered, in Pod source, to end with (and contain) the newline(s) that end it, it should be processed as ending with (and containing) the period character that ends this sentence. (TBT)
Pod パーサは、エラーを報告するときは、単に段落番号を報告する ("Nested E<>'s in Paragraph #52 of Thing/Foo.pm!") のではなく、 およその行番号を報告するための 努力を行うべきです ("Nested E<>'s in Paragraph #52, near line 633 of Thing/Foo.pm!")(should)。 これが難しいところでは、段落番号は少なくとも段落の抜粋と共に 報告されるべきです ("Nested E<>'s in Paragraph #52 of Thing/Foo.pm, which begins 'Read/write accessor for the C<interest rate> attribute...'")(should)。
Pod パーサは、連続したそのままの段落を処理するときには、 たまたま空行を含んでいる大きな一つのそのままの段落として扱うべきです(should)。 つまり、以下のような、空行を挟んだ 2 つの行は:
use Foo;
print Foo->VERSION
フォーマッタや他のプロセッサに渡される前に一つの段落 ("\tuse Foo;\n\n\tprint Foo->VERSION") 統合されるべきです(should)。 パーサはこれを上書きするオプションを許してもかまいません(may)。
これはイベントベースの Pod パーサを実装するには厄介すぎるかもしれない 一方、パース木を返すパーサにとっては直感的です。
Pod フォーマッタは、可能なところでは、短いそのままの段落 (例えば 12 行 以下) がページをまたぐことを避けるように勧めます。
Pod parsers must treat a line with only spaces and/or tabs on it as a "blank line" such as separates paragraphs. (Some older parsers recognized only two adjacent newlines as a "blank line" but would not recognize a newline, a space, and a newline, as a blank line. This is noncompliant behavior.) (TBT)
Authors of Pod formatters/processors should make every effort to avoid writing their own Pod parser. There are already several in CPAN, with a wide range of interface styles -- and one of them, Pod::Parser, comes with modern versions of Perl. (TBT)
Characters in Pod documents may be conveyed either as literals, or by number in E<n> codes, or by an equivalent mnemonic, as in E<eacute> which is exactly equivalent to E<233>. (TBT)
Characters in the range 32-126 refer to those well known US-ASCII characters (also defined there by Unicode, with the same meaning), which all Pod formatters must render faithfully. Characters in the ranges 0-31 and 127-159 should not be used (neither as literals, nor as E<number> codes), except for the literal byte-sequences for newline (13, 13 10, or 10), and tab (9). (TBT)
Characters in the range 160-255 refer to Latin-1 characters (also defined there by Unicode, with the same meaning). Characters above 255 should be understood to refer to Unicode characters. (TBT)
Be warned that some formatters cannot reliably render characters outside 32-126; and many are able to handle 32-126 and 160-255, but nothing above 255. (TBT)
Besides the well-known "E<lt>" and "E<gt>" codes for less-than and greater-than, Pod parsers must understand "E<sol>" for "/" (solidus, slash), and "E<verbar>" for "|" (vertical bar, pipe). Pod parsers should also understand "E<lchevron>" and "E<rchevron>" as legacy codes for characters 171 and 187, i.e., "left-pointing double angle quotation mark" = "left pointing guillemet" and "right-pointing double angle quotation mark" = "right pointing guillemet". (These look like little "<<" and ">>", and they are now preferably expressed with the HTML/XHTML codes "E<laquo>" and "E<raquo>".) (TBT)
Pod parsers should understand all "E<html>" codes as defined
in the entity declarations in the most recent XHTML specification at
www.W3.org. Pod parsers must understand at least the entities
that define characters in the range 160-255 (Latin-1). Pod parsers,
when faced with some unknown "E<identifier>" code,
shouldn't simply replace it with nullstring (by default, at least),
but may pass it through as a string consisting of the literal characters
E, less-than, identifier, greater-than. Or Pod parsers may offer the
alternative option of processing such unknown
"E<identifier>" codes by firing an event especially
for such codes, or by adding a special node-type to the in-memory
document tree. Such "E<identifier>" may have special meaning
to some processors, or some processors may choose to add them to
a special error report.
(TBT)
Pod parsers must also support the XHTML codes "E<quot>" for character 34 (doublequote, "), "E<amp>" for character 38 (ampersand, &), and "E<apos>" for character 39 (apostrophe, '). (TBT)
Note that in all cases of "E<whatever>", whatever (whether
an htmlname, or a number in any base) must consist only of
alphanumeric characters -- that is, whatever must watch
m/\A\w+\z/. So "E< 0 1 2 3 >" is invalid, because
it contains spaces, which aren't alphanumeric characters. This
presumably does not need special treatment by a Pod processor;
" 0 1 2 3 " doesn't look like a number in any base, so it would
presumably be looked up in the table of HTML-like names. Since
there isn't (and cannot be) an HTML-like entity called " 0 1 2 3 ",
this will be treated as an error. However, Pod processors may
treat "E< 0 1 2 3 >" or "E<e-acute>" as syntactically
invalid, potentially earning a different error message than the
error message (or warning, or event) generated by a merely unknown
(but theoretically valid) htmlname, as in "E<qacute>"
[sic]. However, Pod parsers are not required to make this
distinction.
(TBT)
Note that E<number> must not be interpreted as simply "codepoint number in the current/native character set". It always means only "the character represented by codepoint number in Unicode." (This is identical to the semantics of &#number; in XML.) (TBT)
This will likely require many formatters to have tables mapping from treatable Unicode codepoints (such as the "\xE9" for the e-acute character) to the escape sequences or codes necessary for conveying such sequences in the target output format. A converter to *roff would, for example know that "\xE9" (whether conveyed literally, or via a E<...> sequence) is to be conveyed as "e\\*'". Similarly, a program rendering Pod in a Mac OS application window, would presumably need to know that "\xE9" maps to codepoint 142 in MacRoman encoding that (at time of writing) is native for Mac OS. Such Unicode2whatever mappings are presumably already widely available for common output formats. (Such mappings may be incomplete! Implementers are not expected to bend over backwards in an attempt to render Cherokee syllabics, Etruscan runes, Byzantine musical symbols, or any of the other weird things that Unicode can encode.) And if a Pod document uses a character not found in such a mapping, the formatter should consider it an unrenderable character. (TBT)
If, surprisingly, the implementor of a Pod formatter can't find a satisfactory pre-existing table mapping from Unicode characters to escapes in the target format (e.g., a decent table of Unicode characters to *roff escapes), it will be necessary to build such a table. If you are in this circumstance, you should begin with the characters in the range 0x00A0 - 0x00FF, which is mostly the heavily used accented characters. Then proceed (as patience permits and fastidiousness compels) through the characters that the (X)HTML standards groups judged important enough to merit mnemonics for. These are declared in the (X)HTML specifications at the www.W3.org site. At time of writing (September 2001), the most recent entity declaration files are: (TBT)
http://www.w3.org/TR/xhtml1/DTD/xhtml-lat1.ent http://www.w3.org/TR/xhtml1/DTD/xhtml-special.ent http://www.w3.org/TR/xhtml1/DTD/xhtml-symbol.ent
Then you can progress through any remaining notable Unicode characters in the range 0x2000-0x204D (consult the character tables at www.unicode.org), and whatever else strikes your fancy. For example, in xhtml-symbol.ent, there is the entry: (TBT)
<!ENTITY infin "∞"> <!-- infinity, U+221E ISOtech -->
While the mapping "infin" to the character "\x{221E}" will (hopefully) have been already handled by the Pod parser, the presence of the character in this file means that it's reasonably important enough to include in a formatter's table that maps from notable Unicode characters to the codes necessary for rendering them. So for a Unicode-to-*roff mapping, for example, this would merit the entry: (TBT)
"\x{221E}" => '\(in',
It is eagerly hoped that in the future, increasing numbers of formats
(and formatters) will support Unicode characters directly (as (X)HTML
does with ∞, ∞, or ∞), reducing the need
for idiosyncratic mappings of Unicode-to-my_escapes.
(TBT)
It is up to individual Pod formatter to display good judgement when confronted with an unrenderable character (which is distinct from an unknown E<thing> sequence that the parser couldn't resolve to anything, renderable or not). It is good practice to map Latin letters with diacritics (like "E<eacute>"/"E<233>") to the corresponding unaccented US-ASCII letters (like a simple character 101, "e"), but clearly this is often not feasible, and an unrenderable character may be represented as "?", or the like. In attempting a sane fallback (as from E<233> to "e"), Pod formatters may use the %Latin1Code_to_fallback table in Pod::Escapes, or Text::Unidecode, if available. (TBT)
For example, this Pod text: (TBT)
magic is enabled if you set C<$Currency> to 'E<euro>'.
may be rendered as:
"magic is enabled if you set $Currency to '?'" or as
"magic is enabled if you set $Currency to '[euro]'", or as
"magic is enabled if you set $Currency to '[x20AC]', etc.
(TBT)
A Pod formatter may also note, in a comment or warning, a list of what unrenderable characters were encountered. (TBT)
E<...> may freely appear in any formatting code (other than in another E<...> or in an Z<>). That is, "X<The E<euro>1,000,000 Solution>" is valid, as is "L<The E<euro>1,000,000 Solution|Million::Euros>". (TBT)
Some Pod formatters output to formats that implement non-breaking spaces as an individual character (which I'll call "NBSP"), and others output to formats that implement non-breaking spaces just as spaces wrapped in a "don't break this across lines" code. Note that at the level of Pod, both sorts of codes can occur: Pod can contain a NBSP character (whether as a literal, or as a "E<160>" or "E<nbsp>" code); and Pod can contain "S<foo I<bar> baz>" codes, where "mere spaces" (character 32) in such codes are taken to represent non-breaking spaces. Pod parsers should consider supporting the optional parsing of "S<foo I<bar> baz>" as if it were "fooNBSPI<bar>NBSPbaz", and, going the other way, the optional parsing of groups of words joined by NBSP's as if each group were in a S<...> code, so that formatters may use the representation that maps best to what the output format demands. (TBT)
Some processors may find that the S<...> code is easiest to
implement by replacing each space in the parse tree under the content
of the S, with an NBSP. But note: the replacement should apply not to
spaces in all text, but only to spaces in printable text. (This
distinction may or may not be evident in the particular tree/event
model implemented by the Pod parser.) For example, consider this
unusual case:
(TBT)
S<L</Autoloaded Functions>>
This means that the space in the middle of the visible link text must not be broken across lines. In other words, it's the same as this: (TBT)
L<"AutoloadedE<160>Functions"/Autoloaded Functions>
However, a misapplied space-to-NBSP replacement could (wrongly) produce something equivalent to this: (TBT)
L<"AutoloadedE<160>Functions"/AutoloadedE<160>Functions>
...which is almost definitely not going to work as a hyperlink (assuming this formatter outputs a format supporting hypertext). (TBT)
Formatters may choose to just not support the S format code, especially in cases where the output format simply has no NBSP character/code and no code for "don't break this stuff across lines". (TBT)
Besides the NBSP character discussed above, implementors are reminded
of the existence of the other "special" character in Latin-1, the
"soft hyphen" character, also known as "discretionary hyphen",
i.e. E<173> = E<0xAD> =
E<shy>). This character expresses an optional hyphenation
point. That is, it normally renders as nothing, but may render as a
"-" if a formatter breaks the word at that point. Pod formatters
should, as appropriate, do one of the following: 1) render this with
a code with the same meaning (e.g., "\-" in RTF), 2) pass it through
in the expectation that the formatter understands this character as
such, or 3) delete it.
(TBT)
For example: (TBT)
sigE<shy>action manuE<shy>script JarkE<shy>ko HieE<shy>taE<shy>nieE<shy>mi
These signal to a formatter that if it is to hyphenate "sigaction"
or "manuscript", then it should be done as
"sig-[linebreak]action" or "manu-[linebreak]script"
(and if it doesn't hyphenate it, then the E<shy> doesn't
show up at all). And if it is
to hyphenate "Jarkko" and/or "Hietaniemi", it can do
so only at the points where there is a E<shy> code.
(TBT)
In practice, it is anticipated that this character will not be used often, but formatters should either support it, or delete it. (TBT)
If you think that you want to add a new command to Pod (like, say, a "=biblio" command), consider whether you could get the same effect with a for or begin/end sequence: "=for biblio ..." or "=begin biblio" ... "=end biblio". Pod processors that don't understand "=for biblio", etc, will simply ignore it, whereas they may complain loudly if they see "=biblio". (TBT)
Throughout this document, "Pod" has been the preferred spelling for the name of the documentation format. One may also use "POD" or "pod". For the documentation that is (typically) in the Pod format, you may use "pod", or "Pod", or "POD". Understanding these distinctions is useful; but obsessing over how to spell them, usually is not. (TBT)
As you can tell from a glance at perlpod, the L<...> code is the most complex of the Pod formatting codes. The points below will hopefully clarify what it means and how processors should deal with it. (TBT)
In parsing an L<...> code, Pod parsers must distinguish at least four attributes: (TBT)
The link-text. If there is none, this must be undef. (E.g., in "L<Perl Functions|perlfunc>", the link-text is "Perl Functions". In "L<Time::HiRes>" and even "L<|Time::HiRes>", there is no link text. Note that link text may contain formatting.) (TBT)
The possibly inferred link-text; i.e., if there was no real link text, then this is the text that we'll infer in its place. (E.g., for "L<Getopt::Std>", the inferred link text is "Getopt::Std".) (TBT)
The name or URL, or undef if none. (E.g., in "L<Perl Functions|perlfunc>", the name (also sometimes called the page) is "perlfunc". In "L</CAVEATS>", the name is undef.) (TBT)
The section (AKA "item" in older perlpods), or undef if none. E.g., in "L<Getopt::Std/DESCRIPTION>", "DESCRIPTION" is the section. (Note that this is not the same as a manpage section like the "5" in "man 5 crontab". "Section Foo" in the Pod sense means the part of the text that's introduced by the heading or item whose text is "Foo".) (TBT)
Pod parsers may also note additional attributes including: (TBT)
A flag for whether item 3 (if present) is a URL (like "http://lists.perl.org" is), in which case there should be no section attribute; a Pod name (like "perldoc" and "Getopt::Std" are); or possibly a man page name (like "crontab(5)" is). (TBT)
The raw original L<...> content, before text is split on "|", "/", etc, and before E<...> codes are expanded. (TBT)
(The above were numbered only for concise reference below. It is not a requirement that these be passed as an actual list or array.) (TBT)
For example: (TBT)
L<Foo::Bar>
=> undef, # link text
"Foo::Bar", # possibly inferred link text
"Foo::Bar", # name
undef, # section
'pod', # what sort of link
"Foo::Bar" # original content
L<Perlport's section on NL's|perlport/Newlines>
=> "Perlport's section on NL's", # link text
"Perlport's section on NL's", # possibly inferred link text
"perlport", # name
"Newlines", # section
'pod', # what sort of link
"Perlport's section on NL's|perlport/Newlines" # orig. content
L<perlport/Newlines>
=> undef, # link text
'"Newlines" in perlport', # possibly inferred link text
"perlport", # name
"Newlines", # section
'pod', # what sort of link
"perlport/Newlines" # original content
L<crontab(5)/"DESCRIPTION">
=> undef, # link text
'"DESCRIPTION" in crontab(5)', # possibly inferred link text
"crontab(5)", # name
"DESCRIPTION", # section
'man', # what sort of link
'crontab(5)/"DESCRIPTION"' # original content
L</Object Attributes>
=> undef, # link text
'"Object Attributes"', # possibly inferred link text
undef, # name
"Object Attributes", # section
'pod', # what sort of link
"/Object Attributes" # original content
L<http://www.perl.org/>; => undef, # link text "http://www.perl.org/";, # possibly inferred link text "http://www.perl.org/";, # name undef, # section 'url', # what sort of link "http://www.perl.org/"; # original content
L<Perl.org|http://www.perl.org/>; => "Perl.org", # link text "http://www.perl.org/";, # possibly inferred link text "http://www.perl.org/";, # name undef, # section 'url', # what sort of link "Perl.org|http://www.perl.org/"; # original content
Note that you can distinguish URL-links from anything else by the
fact that they match m/\A\w+:[^:\s]\S*\z/. So
L<http://www.perl.com> is a URL, but
L<HTTP::Response> isn't.
(TBT)
In case of L<...> codes with no "text|" part in them,
older formatters have exhibited great variation in actually displaying
the link or cross reference. For example, L<crontab(5)> would render
as "the crontab(5) manpage", or "in the crontab(5) manpage"
or just "crontab(5)".
(TBT)
Pod processors must now treat "text|"-less links as follows: (TBT)
L<name> => L<name|name> L</section> => L<"section"|/section> L<name/section> => L<"section" in name|name/section>
Note that section names might contain markup. I.e., if a section starts with: (TBT)
=head2 About the C<-M> Operator
or with: (TBT)
=item About the C<-M> Operator
then a link to it would look like this: (TBT)
L<somedoc/About the C<-M> Operator>
Formatters may choose to ignore the markup for purposes of resolving the link and use only the renderable characters in the section name, as in: (TBT)
<h1><a name="About_the_-M_Operator">About the <code>-M</code> Operator</h1>
...
<a href="somedoc#About_the_-M_Operator">About the <code>-M</code> Operator" in somedoc</a>
Previous versions of perlpod distinguished L<name/"section">
links from L<name/item> links (and their targets). These
have been merged syntactically and semantically in the current
specification, and section can refer either to a "=headn Heading
Content" command or to a "=item Item Content" command. This
specification does not specify what behavior should be in the case
of a given document having several things all seeming to produce the
same section identifier (e.g., in HTML, several things all producing
the same anchorname in <a name="anchorname">...</a>
elements). Where Pod processors can control this behavior, they should
use the first such anchor. That is, L<Foo/Bar> refers to the
first "Bar" section in Foo.
(TBT)
But for some processors/formats this cannot be easily controlled; as with the HTML example, the behavior of multiple ambiguous <a name="anchorname">...</a> is most easily just left up to browsers to decide. (TBT)
Authors wanting to link to a particular (absolute) URL, must do so only with "L<scheme:...>" codes (like L<http://www.perl.org>), and must not attempt "L<Some Site Name|scheme:...>" codes. This restriction avoids many problems in parsing and rendering L<...> codes. (TBT)
In a L<text|...> code, text may contain formatting codes
for formatting or for E<...> escapes, as in:
(TBT)
L<B<ummE<234>stuff>|...>
For L<...> codes without a "name|" part, only
E<...> and Z<> codes may occur. That is,
authors should not use "L<B<Foo::Bar>>".
(TBT)
Note, however, that formatting codes and Z<>'s can occur in any and all parts of an L<...> (i.e., in name, section, text, and url). (TBT)
Authors must not nest L<...> codes. For example, "L<The L<Foo::Bar> man page>" should be treated as an error. (TBT)
Note that Pod authors may use formatting codes inside the "text" part of "L<text|name>" (and so on for L<text|/"sec">). (TBT)
In other words, this is valid: (TBT)
Go read L<the docs on C<$.>|perlvar/"$.">
Some output formats that do allow rendering "L<...>" codes as hypertext, might not allow the link-text to be formatted; in that case, formatters will have to just ignore that formatting. (TBT)
At time of writing, L<name> values are of two types:
either the name of a Pod page like L<Foo::Bar> (which
might be a real Perl module or program in an @INC / PATH
directory, or a .pod file in those places); or the name of a Unix
man page, like L<crontab(5)>. In theory, L<chmod>
in ambiguous between a Pod page called "chmod", or the Unix man page
"chmod" (in whatever man-section). However, the presence of a string
in parens, as in "crontab(5)", is sufficient to signal that what
is being discussed is not a Pod page, and so is presumably a
Unix man page. The distinction is of no importance to many
Pod processors, but some processors that render to hypertext formats
may need to distinguish them in order to know how to render a
given L<foo> code.
(TBT)
Previous versions of perlpod allowed for a L<section> syntax (as in
L<Object Attributes>), which was not easily distinguishable from
L<name> syntax and for L<"section"> which was only
slightly less ambiguous. This syntax is no longer in the specification, and
has been replaced by the L</section> syntax (where the slash was
formerly optional). Pod parsers should tolerate the L<"section">
syntax, for a while at least. The suggested heuristic for distinguishing
L<section> from L<name> is that if it contains any
whitespace, it's a section. Pod processors should warn about this being
deprecated syntax.
(TBT)
"=over"..."=back" 領域は、様々な種類のリスト風の構造に使われます。 (ここでは、「領域」という用語は単に "=over" からそれに対応する "=back" までの全てを含むものという意味使っています。)
The non-zero numeric indentlevel in "=over indentlevel" ...
"=back" is used for giving the formatter a clue as to how many
"spaces" (ems, or roughly equivalent units) it should tab over,
although many formatters will have to convert this to an absolute
measurement that may not exactly match with the size of spaces (or M's)
in the document's base font. Other formatters may have to completely
ignore the number. The lack of any explicit indentlevel parameter is
equivalent to an indentlevel value of 4. Pod processors may
complain if indentlevel is present but is not a positive number
matching m/\A(\d*\.)?\d+\z/.
(TBT)
Authors of Pod formatters are reminded that "=over" ... "=back" may map to several different constructs in your output format. For example, in converting Pod to (X)HTML, it can map to any of <ul>...</ul>, <ol>...</ol>, <dl>...</dl>, or <blockquote>...</blockquote>. Similarly, "=item" can map to <li> or <dt>. (TBT)
それぞれの "=over" ... "=back" 領域は以下のうちの一つであるべきです(should):
"=item *" 段落および、 通常の段落、そのままの段落、ネストした "=over" ... "=back" 領域、"=for..." 段落、"=begin"..."=end" コード のいずれかが任意の数引き続いたもののみからなる "=over" ... "=back" 領域。
(Pod プロセッサは、生の "=item" を、"=item *" であるかのように 扱わなければなりません(must)。) "*" をそのままアスタリスクとして表示するか、"o" を使うか、あるいは ある種の実際の黒丸を使うかは Pod フォーマッタに任されていて、 これはネストレベルに依存するかも知れません。
m/\A=item\s+\d+\.?\s*\z/ 段落および、
通常の段落、そのままの段落、ネストした
"=over" ... "=back" 領域、"=for..." 段落、"=begin"..."=end" コード
のいずれかが任意の数引き続いたもののみからなる "=over" ... "=back" 領域。
各章の番号は 1 から始まり、省略されることなく続かなければならないことに
注意してください。
(Pod プロセッサは、"=item 1" のような行を、ピリオド付きの "=item 1." であるかのように扱わなければなりません(must)。)
"=item [text]" 段落および、 通常の段落、そのままの段落、ネストした "=over" ... "=back" 領域、"=for..." 段落、"=begin"..."=end" コード のいずれかが任意の数引き続いたもののみからなる "=over" ... "=back" 領域。
"=item [text]" 段落は、
m/\A=item\s+\d+\.?\s*\z/, m/\A=item\s+\*\s*\z/,
match just m/\A=item\s*\z/ にマッチングするべきではありません。
An "=over" ... "=back" region containing no "=item" paragraphs at all, and containing only some number of ordinary/verbatim paragraphs, and possibly also some nested "=over" ... "=back" regions, "=for..." paragraphs, and "=begin"..."=end" regions. Such an itemless "=over" ... "=back" region in Pod is equivalent in meaning to a "<blockquote>...</blockquote>" element in HTML. (TBT)
上述の全ての場合において、"=over" コマンドの後の ("=cut" と "=pod" を 除く) 最初の Pod 段落を調べることで、どの形式の "=over" ... "=back" であるかを決定できることに注意してください。
Pod フォーマッタは "=item text..." に任意の長さのテキストを 許容 しなければなりません (must)。 実際には、このような段落のほとんどは以下のような短いものです:
=item For cutting off our trade with all parts of the world
しかし任意に長くなるかも知れません:
=item For transporting us beyond seas to be tried for pretended offenses
=item He is at this time transporting large armies of foreign mercenaries to complete the works of death, desolation and tyranny, already begun with circumstances of cruelty and perfidy scarcely paralleled in the most barbarous ages, and totally unworthy the head of a civilized nation.
Pod プロセッサは、対応する段落のない "=item *" / "=item number" コマンドを許容するべきです(should)。 中間の item が例です:
=over
=item 1
Pick up dry cleaning.
=item 2
=item 3
Stop by the store. Get Abba Zabas, Stoli, and cheap lawn chairs.
=back
"=over" ... "=back" 領域に見出しを含めることはできません。 プロセッサはそのような見出しをエラーとして扱うことができます(may)。
"=over" ... "=back" 領域には内容があるべきであることに注意してください。 つまり、作者は以下のような空の領域を作るべきではありません:
=over
=back
Pod プロセッサがこのような、内容のない "=over" ... "=back" 領域を 発見した場合、無視してもかまいません(may)し、エラーとして 報告してもかまいません(may)。
プロセッサは、文書の末尾まで続く(つまり対応する "=back" がない) "=over" リストを許容しなければなりません(must)が、そのようなリストに 警告を出してもかまいません(may)。
Pod フォーマッタの作者はこのような構造に注意するべきです:
=item Neque
=item Porro
=item Quisquam Est
Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem.
=item Ut Enim
is semantically ambiguous, in a way that makes formatting decisions a bit difficult. On the one hand, it could be mention of an item "Neque", mention of another item "Porro", and mention of another item "Quisquam Est", with just the last one requiring the explanatory paragraph "Qui dolorem ipsum quia dolor..."; and then an item "Ut Enim". In that case, you'd want to format it like so: (TBT)
Neque
Porro
Quisquam Est
Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci
velit, sed quia non numquam eius modi tempora incidunt ut
labore et dolore magnam aliquam quaerat voluptatem.
Ut Enim
But it could equally well be a discussion of three (related or equivalent) items, "Neque", "Porro", and "Quisquam Est", followed by a paragraph explaining them all, and then a new item "Ut Enim". In that case, you'd probably want to format it like so: (TBT)
Neque
Porro
Quisquam Est
Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci
velit, sed quia non numquam eius modi tempora incidunt ut
labore et dolore magnam aliquam quaerat voluptatem.
Ut Enim
But (for the foreseeable future), Pod does not provide any way for Pod authors to distinguish which grouping is meant by the above "=item"-cluster structure. So formatters should format it like so: (TBT)
Neque
Porro
Quisquam Est
Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci
velit, sed quia non numquam eius modi tempora incidunt ut
labore et dolore magnam aliquam quaerat voluptatem.
Ut Enim
That is, there should be (at least roughly) equal spacing between items as between paragraphs (although that spacing may well be less than the full height of a line of text). This leaves it to the reader to use (con)textual cues to figure out whether the "Qui dolorem ipsum..." paragraph applies to the "Quisquam Est" item or to all three items "Neque", "Porro", and "Quisquam Est". While not an ideal situation, this is preferable to providing formatting cues that may be actually contrary to the author's intent. (TBT)
データ段落は典型的には used for inlining non-Pod data that is to be used (typically passed through) when rendering the document to a specific format: (TBT)
=begin rtf
\par{\pard\qr\sa4500{\i Printed\~\chdate\~\chtime}\par}
=end rtf
正確に同じ効果は、偶然ながら、単一の "=for" 段落でも達成できます:
=for rtf \par{\pard\qr\sa4500{\i Printed\~\chdate\~\chtime}\par}
(これは形式的にはデータ段落ではありませんが、同じ意味を持ち、 Pod パーサは同じようにパースするでしょう。)
データ段落のもう一つの例です:
=begin html
I like <em>PIE</em>!
<hr>Especially pecan pie!
=end html
通常の段落の場合、Pod パーサは (最初の段落にある) "E</em>" を "E<lt>" や "E<eacute>" と同じように、 フォーマッティングコードとして展開しようとします。 しかし、これは "=begin identifier"..."=end identifier" 領域の 中にあり、かつ 識別子 "html" は ":" 接頭辞で始まっていないので、 この領域の内容は、通常の段落(あるいは、もしスペースやタブで 始まっている場合はそのままの段落)としてされるのではなく、データ段落として 保管されます。
As a further example: At time of writing, no "biblio" identifier is supported, but suppose some processor were written to recognize it as a way of (say) denoting a bibliographic reference (necessarily containing formatting codes in ordinary paragraphs). The fact that "biblio" paragraphs were meant for ordinary processing would be indicated by prefacing each "biblio" identifier with a colon: (TBT)
=begin :biblio
Wirth, Niklaus. 1976. I<Algorithms + Data Structures = Programs.> Prentice-Hall, Englewood Cliffs, NJ.
=end :biblio
This would signal to the parser that paragraphs in this begin...end region are subject to normal handling as ordinary/verbatim paragraphs (while still tagged as meant only for processors that understand the "biblio" identifier). The same effect could be had with: (TBT)
=for :biblio Wirth, Niklaus. 1976. I<Algorithms + Data Structures = Programs.> Prentice-Hall, Englewood Cliffs, NJ.
The ":" on these identifiers means simply "process this stuff normally, even though the result will be for some special target". I suggest that parser APIs report "biblio" as the target identifier, but also report that it had a ":" prefix. (And similarly, with the above "html", report "html" as the target identifier, and note the lack of a ":" prefix.) (TBT)
identifier がコロンで始まっている "=begin identifier"..."=end identifier" 領域は、コマンドを含むことが できる ことに注意してください。 例えば:
=begin :biblio
Wirth's classic is available in several editions, including:
=for comment hm, check abebooks.com for how much used copies cost.
=over
=item
Wirth, Niklaus. 1975. I<Algorithmen und Datenstrukturen.> Teubner, Stuttgart. [Yes, it's in German.]
=item
Wirth, Niklaus. 1976. I<Algorithms + Data Structures = Programs.> Prentice-Hall, Englewood Cliffs, NJ.
=back
=end :biblio
Note, however, a "=begin identifier"..."=end identifier" region where identifier does not begin with a colon, should not directly contain "=head1" ... "=head4" commands, nor "=over", nor "=back", nor "=item". For example, this may be considered invalid: (TBT)
=begin somedata
This is a data paragraph.
=head1 Don't do this!
This is a data paragraph too.
=end somedata
A Pod processor may signal that the above (specifically the "=head1" paragraph) is an error. Note, however, that the following should not be treated as an error: (TBT)
=begin somedata
This is a data paragraph.
=cut
# Yup, this isn't Pod anymore.
sub excl { (rand() > .5) ? "hoo!" : "hah!" }
=pod
This is a data paragraph too.
=end somedata
そしてこれも正当です:
=begin someformat
This is a data paragraph.
And this is a data paragraph.
=begin someotherformat
This is a data paragraph too.
And this is a data paragraph too.
=begin :yetanotherformat
=head2 This is a command paragraph!
This is an ordinary paragraph!
And this is a verbatim paragraph!
=end :yetanotherformat
=end someotherformat
Another data paragraph!
=end someformat
The contents of the above "=begin :yetanotherformat" ... "=end :yetanotherformat" region aren't data paragraphs, because the immediately containing region's identifier (":yetanotherformat") begins with a colon. In practice, most regions that contain data paragraphs will contain only data paragraphs; however, the above nesting is syntactically valid as Pod, even if it is rare. However, the handlers for some formats, like "html", will accept only data paragraphs, not nested regions; and they may complain if they see (targeted for them) nested regions, or commands, other than "=end", "=pod", and "=cut". (TBT)
また、以下の正当な構造を考えてみます:
=begin :biblio
Wirth's classic is available in several editions, including:
=over
=item
Wirth, Niklaus. 1975. I<Algorithmen und Datenstrukturen.> Teubner, Stuttgart. [Yes, it's in German.]
=item
Wirth, Niklaus. 1976. I<Algorithms + Data Structures = Programs.> Prentice-Hall, Englewood Cliffs, NJ.
=back
Buy buy buy!
=begin html
<img src='wirth_spokesmodeling_book.png'>
<hr>
=end html
Now now now!
=end :biblio
There, the "=begin html"..."=end html" region is nested inside the larger "=begin :biblio"..."=end :biblio" region. Note that the content of the "=begin html"..."=end html" region is data paragraph(s), because the immediately containing region's identifier ("html") doesn't begin with a colon. (TBT)
Pod parsers, when processing a series of data paragraphs one after another (within a single region), should consider them to be one large data paragraph that happens to contain blank lines. So the content of the above "=begin html"..."=end html" may be stored as two data paragraphs (one consisting of "<img src='wirth_spokesmodeling_book.png'>\n" and another consisting of "<hr>\n"), but should be stored as a single data paragraph (consisting of "<img src='wirth_spokesmodeling_book.png'>\n\n<hr>\n"). (TBT)
Pod processors should tolerate empty "=begin something"..."=end something" regions, empty "=begin :something"..."=end :something" regions, and contentless "=for something" and "=for :something" paragraphs. I.e., these should be tolerated: (TBT)
=for html
=begin html
=end html
=begin :biblio
=end :biblio
Incidentally, note that there's no easy way to express a data paragraph starting with something that looks like a command. Consider: (TBT)
=begin stuff
=shazbot
=end stuff
There, "=shazbot" will be parsed as a Pod command "shazbot", not as a data paragraph "=shazbot\n". However, you can express a data paragraph consisting of "=shazbot\n" using this code: (TBT)
=for stuff =shazbot
これが必要な状況は、おそらくかなり稀です。