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2
3=head1 NAME
4
5perlpodspec - Plain Old Documentation: format specification and notes
6
7=head1 DESCRIPTION
8
9This document is detailed notes on the Pod markup language. Most
10people will only have to read L<perlpod|perlpod> to know how to write
11in Pod, but this document may answer some incidental questions to do
12with parsing and rendering Pod.
13
14In this document, "must" / "must not", "should" /
15"should not", and "may" have their conventional (cf. RFC 2119)
16meanings: "X must do Y" means that if X doesn't do Y, it's against
17this specification, and should really be fixed. "X should do Y"
18means that it's recommended, but X may fail to do Y, if there's a
19good reason. "X may do Y" is merely a note that X can do Y at
20will (although it is up to the reader to detect any connotation of
21"and I think it would be I<nice> if X did Y" versus "it wouldn't
22really I<bother> me if X did Y").
23
24Notably, when I say "the parser should do Y", the
25parser may fail to do Y, if the calling application explicitly
26requests that the parser I<not> do Y. I often phrase this as
27"the parser should, by default, do Y." This doesn't I<require>
28the parser to provide an option for turning off whatever
29feature Y is (like expanding tabs in verbatim paragraphs), although
30it implicates that such an option I<may> be provided.
31
32=head1 Pod Definitions
33
ac036724 34Pod is embedded in files, typically Perl source files, although you
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35can write a file that's nothing but Pod.
36
37A B<line> in a file consists of zero or more non-newline characters,
38terminated by either a newline or the end of the file.
39
40A B<newline sequence> is usually a platform-dependent concept, but
41Pod parsers should understand it to mean any of CR (ASCII 13), LF
42(ASCII 10), or a CRLF (ASCII 13 followed immediately by ASCII 10), in
43addition to any other system-specific meaning. The first CR/CRLF/LF
44sequence in the file may be used as the basis for identifying the
45newline sequence for parsing the rest of the file.
46
47A B<blank line> is a line consisting entirely of zero or more spaces
48(ASCII 32) or tabs (ASCII 9), and terminated by a newline or end-of-file.
49A B<non-blank line> is a line containing one or more characters other
50than space or tab (and terminated by a newline or end-of-file).
51
52(I<Note:> Many older Pod parsers did not accept a line consisting of
ac036724 53spaces/tabs and then a newline as a blank line. The only lines they
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54considered blank were lines consisting of I<no characters at all>,
55terminated by a newline.)
56
57B<Whitespace> is used in this document as a blanket term for spaces,
58tabs, and newline sequences. (By itself, this term usually refers
59to literal whitespace. That is, sequences of whitespace characters
60in Pod source, as opposed to "EE<lt>32>", which is a formatting
61code that I<denotes> a whitespace character.)
62
63A B<Pod parser> is a module meant for parsing Pod (regardless of
64whether this involves calling callbacks or building a parse tree or
65directly formatting it). A B<Pod formatter> (or B<Pod translator>)
66is a module or program that converts Pod to some other format (HTML,
67plaintext, TeX, PostScript, RTF). A B<Pod processor> might be a
68formatter or translator, or might be a program that does something
353c6505 69else with the Pod (like counting words, scanning for index points,
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70etc.).
71
72Pod content is contained in B<Pod blocks>. A Pod block starts with a
1bca558f 73line that matches C<m/\A=[a-zA-Z]/>, and continues up to the next line
ac036724 74that matches C<m/\A=cut/> or up to the end of the file if there is
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75no C<m/\A=cut/> line.
76
77=for comment
78 The current perlsyn says:
79 [beginquote]
80 Note that pod translators should look at only paragraphs beginning
81 with a pod directive (it makes parsing easier), whereas the compiler
82 actually knows to look for pod escapes even in the middle of a
83 paragraph. This means that the following secret stuff will be ignored
84 by both the compiler and the translators.
85 $a=3;
86 =secret stuff
87 warn "Neither POD nor CODE!?"
88 =cut back
89 print "got $a\n";
90 You probably shouldn't rely upon the warn() being podded out forever.
91 Not all pod translators are well-behaved in this regard, and perhaps
92 the compiler will become pickier.
93 [endquote]
94 I think that those paragraphs should just be removed; paragraph-based
95 parsing seems to have been largely abandoned, because of the hassle
96 with non-empty blank lines messing up what people meant by "paragraph".
97 Even if the "it makes parsing easier" bit were especially true,
98 it wouldn't be worth the confusion of having perl and pod2whatever
99 actually disagree on what can constitute a Pod block.
100
101Within a Pod block, there are B<Pod paragraphs>. A Pod paragraph
102consists of non-blank lines of text, separated by one or more blank
103lines.
104
105For purposes of Pod processing, there are four types of paragraphs in
106a Pod block:
107
108=over
109
110=item *
111
112A command paragraph (also called a "directive"). The first line of
113this paragraph must match C<m/\A=[a-zA-Z]/>. Command paragraphs are
114typically one line, as in:
115
116 =head1 NOTES
117
118 =item *
119
120But they may span several (non-blank) lines:
121
122 =for comment
123 Hm, I wonder what it would look like if
124 you tried to write a BNF for Pod from this.
210b36aa 125
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126 =head3 Dr. Strangelove, or: How I Learned to
127 Stop Worrying and Love the Bomb
128
129I<Some> command paragraphs allow formatting codes in their content
130(i.e., after the part that matches C<m/\A=[a-zA-Z]\S*\s*/>), as in:
131
132 =head1 Did You Remember to C<use strict;>?
133
134In other words, the Pod processing handler for "head1" will apply the
135same processing to "Did You Remember to CE<lt>use strict;>?" that it
ac036724 136would to an ordinary paragraph (i.e., formatting codes like
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137"CE<lt>...>") are parsed and presumably formatted appropriately, and
138whitespace in the form of literal spaces and/or tabs is not
139significant.
140
141=item *
142
143A B<verbatim paragraph>. The first line of this paragraph must be a
144literal space or tab, and this paragraph must not be inside a "=begin
145I<identifier>", ... "=end I<identifier>" sequence unless
146"I<identifier>" begins with a colon (":"). That is, if a paragraph
147starts with a literal space or tab, but I<is> inside a
148"=begin I<identifier>", ... "=end I<identifier>" region, then it's
149a data paragraph, unless "I<identifier>" begins with a colon.
150
151Whitespace I<is> significant in verbatim paragraphs (although, in
152processing, tabs are probably expanded).
153
154=item *
155
156An B<ordinary paragraph>. A paragraph is an ordinary paragraph
157if its first line matches neither C<m/\A=[a-zA-Z]/> nor
158C<m/\A[ \t]/>, I<and> if it's not inside a "=begin I<identifier>",
159... "=end I<identifier>" sequence unless "I<identifier>" begins with
160a colon (":").
161
162=item *
163
164A B<data paragraph>. This is a paragraph that I<is> inside a "=begin
165I<identifier>" ... "=end I<identifier>" sequence where
166"I<identifier>" does I<not> begin with a literal colon (":"). In
167some sense, a data paragraph is not part of Pod at all (i.e.,
168effectively it's "out-of-band"), since it's not subject to most kinds
169of Pod parsing; but it is specified here, since Pod
170parsers need to be able to call an event for it, or store it in some
171form in a parse tree, or at least just parse I<around> it.
172
173=back
174
175For example: consider the following paragraphs:
176
177 # <- that's the 0th column
178
179 =head1 Foo
210b36aa 180
8a93676d 181 Stuff
210b36aa 182
8a93676d 183 $foo->bar
210b36aa 184
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185 =cut
186
187Here, "=head1 Foo" and "=cut" are command paragraphs because the first
188line of each matches C<m/\A=[a-zA-Z]/>. "I<[space][space]>$foo->bar"
189is a verbatim paragraph, because its first line starts with a literal
190whitespace character (and there's no "=begin"..."=end" region around).
191
192The "=begin I<identifier>" ... "=end I<identifier>" commands stop
6fbdb1cc 193paragraphs that they surround from being parsed as ordinary or verbatim
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194paragraphs, if I<identifier> doesn't begin with a colon. This
195is discussed in detail in the section
196L</About Data Paragraphs and "=beginE<sol>=end" Regions>.
197
198=head1 Pod Commands
199
200This section is intended to supplement and clarify the discussion in
201L<perlpod/"Command Paragraph">. These are the currently recognized
202Pod commands:
203
204=over
205
206=item "=head1", "=head2", "=head3", "=head4"
207
208This command indicates that the text in the remainder of the paragraph
209is a heading. That text may contain formatting codes. Examples:
210
211 =head1 Object Attributes
210b36aa 212
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213 =head3 What B<Not> to Do!
214
215=item "=pod"
216
217This command indicates that this paragraph begins a Pod block. (If we
218are already in the middle of a Pod block, this command has no effect at
219all.) If there is any text in this command paragraph after "=pod",
220it must be ignored. Examples:
221
222 =pod
210b36aa 223
8a93676d 224 This is a plain Pod paragraph.
210b36aa 225
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226 =pod This text is ignored.
227
228=item "=cut"
229
230This command indicates that this line is the end of this previously
231started Pod block. If there is any text after "=cut" on the line, it must be
232ignored. Examples:
233
234 =cut
235
236 =cut The documentation ends here.
237
238 =cut
239 # This is the first line of program text.
240 sub foo { # This is the second.
241
659cfd94 242It is an error to try to I<start> a Pod block with a "=cut" command. In
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243that case, the Pod processor must halt parsing of the input file, and
244must by default emit a warning.
245
246=item "=over"
247
248This command indicates that this is the start of a list/indent
249region. If there is any text following the "=over", it must consist
250of only a nonzero positive numeral. The semantics of this numeral is
251explained in the L</"About =over...=back Regions"> section, further
252below. Formatting codes are not expanded. Examples:
253
254 =over 3
210b36aa 255
8a93676d 256 =over 3.5
210b36aa 257
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258 =over
259
260=item "=item"
261
262This command indicates that an item in a list begins here. Formatting
263codes are processed. The semantics of the (optional) text in the
264remainder of this paragraph are
265explained in the L</"About =over...=back Regions"> section, further
266below. Examples:
267
268 =item
210b36aa 269
8a93676d 270 =item *
210b36aa 271
8a93676d 272 =item *
210b36aa 273
8a93676d 274 =item 14
210b36aa 275
8a93676d 276 =item 3.
210b36aa 277
8a93676d 278 =item C<< $thing->stuff(I<dodad>) >>
210b36aa 279
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280 =item For transporting us beyond seas to be tried for pretended
281 offenses
210b36aa 282
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283 =item He is at this time transporting large armies of foreign
284 mercenaries to complete the works of death, desolation and
285 tyranny, already begun with circumstances of cruelty and perfidy
286 scarcely paralleled in the most barbarous ages, and totally
287 unworthy the head of a civilized nation.
288
289=item "=back"
290
291This command indicates that this is the end of the region begun
292by the most recent "=over" command. It permits no text after the
293"=back" command.
294
295=item "=begin formatname"
296
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297=item "=begin formatname parameter"
298
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299This marks the following paragraphs (until the matching "=end
300formatname") as being for some special kind of processing. Unless
301"formatname" begins with a colon, the contained non-command
302paragraphs are data paragraphs. But if "formatname" I<does> begin
303with a colon, then non-command paragraphs are ordinary paragraphs
304or data paragraphs. This is discussed in detail in the section
305L</About Data Paragraphs and "=beginE<sol>=end" Regions>.
306
307It is advised that formatnames match the regexp
c85e9b4c 308C<m/\A:?[-a-zA-Z0-9_]+\z/>. Everything following whitespace after the
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309formatname is a parameter that may be used by the formatter when dealing
310with this region. This parameter must not be repeated in the "=end"
311paragraph. Implementors should anticipate future expansion in the
312semantics and syntax of the first parameter to "=begin"/"=end"/"=for".
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313
314=item "=end formatname"
315
316This marks the end of the region opened by the matching
317"=begin formatname" region. If "formatname" is not the formatname
318of the most recent open "=begin formatname" region, then this
319is an error, and must generate an error message. This
320is discussed in detail in the section
321L</About Data Paragraphs and "=beginE<sol>=end" Regions>.
322
323=item "=for formatname text..."
324
325This is synonymous with:
326
327 =begin formatname
210b36aa 328
8a93676d 329 text...
210b36aa 330
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331 =end formatname
332
333That is, it creates a region consisting of a single paragraph; that
334paragraph is to be treated as a normal paragraph if "formatname"
335begins with a ":"; if "formatname" I<doesn't> begin with a colon,
336then "text..." will constitute a data paragraph. There is no way
337to use "=for formatname text..." to express "text..." as a verbatim
338paragraph.
339
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340=item "=encoding encodingname"
341
342This command, which should occur early in the document (at least
1e54db1a 343before any non-US-ASCII data!), declares that this document is
a179871b 344encoded in the encoding I<encodingname>, which must be
6fbdb1cc 345an encoding name that L<Encode> recognizes. (Encode's list
8a3f7e95 346of supported encodings, in L<Encode::Supported>, is useful here.)
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347If the Pod parser cannot decode the declared encoding, it
348should emit a warning and may abort parsing the document
349altogether.
350
351A document having more than one "=encoding" line should be
352considered an error. Pod processors may silently tolerate this if
353the not-first "=encoding" lines are just duplicates of the
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354first one (e.g., if there's a "=encoding utf8" line, and later on
355another "=encoding utf8" line). But Pod processors should complain if
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356there are contradictory "=encoding" lines in the same document
357(e.g., if there is a "=encoding utf8" early in the document and
358"=encoding big5" later). Pod processors that recognize BOMs
359may also complain if they see an "=encoding" line
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360that contradicts the BOM (e.g., if a document with a UTF-16LE
361BOM has an "=encoding shiftjis" line).
a179871b 362
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363=back
364
365If a Pod processor sees any command other than the ones listed
366above (like "=head", or "=haed1", or "=stuff", or "=cuttlefish",
367or "=w123"), that processor must by default treat this as an
368error. It must not process the paragraph beginning with that
369command, must by default warn of this as an error, and may
370abort the parse. A Pod parser may allow a way for particular
371applications to add to the above list of known commands, and to
372stipulate, for each additional command, whether formatting
373codes should be processed.
374
375Future versions of this specification may add additional
376commands.
377
378
379
380=head1 Pod Formatting Codes
381
382(Note that in previous drafts of this document and of perlpod,
383formatting codes were referred to as "interior sequences", and
384this term may still be found in the documentation for Pod parsers,
385and in error messages from Pod processors.)
386
387There are two syntaxes for formatting codes:
388
389=over
390
391=item *
392
393A formatting code starts with a capital letter (just US-ASCII [A-Z])
394followed by a "<", any number of characters, and ending with the first
395matching ">". Examples:
396
397 That's what I<you> think!
398
399 What's C<dump()> for?
400
401 X<C<chmod> and C<unlink()> Under Different Operating Systems>
402
403=item *
404
405A formatting code starts with a capital letter (just US-ASCII [A-Z])
406followed by two or more "<"'s, one or more whitespace characters,
407any number of characters, one or more whitespace characters,
408and ending with the first matching sequence of two or more ">"'s, where
409the number of ">"'s equals the number of "<"'s in the opening of this
410formatting code. Examples:
411
412 That's what I<< you >> think!
413
414 C<<< open(X, ">>thing.dat") || die $! >>>
415
416 B<< $foo->bar(); >>
417
418With this syntax, the whitespace character(s) after the "CE<lt><<"
1bca558f 419and before the ">>>" (or whatever letter) are I<not> renderable. They
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420do not signify whitespace, are merely part of the formatting codes
421themselves. That is, these are all synonymous:
422
423 C<thing>
424 C<< thing >>
425 C<< thing >>
426 C<<< thing >>>
427 C<<<<
428 thing
429 >>>>
430
431and so on.
432
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433Finally, the multiple-angle-bracket form does I<not> alter the interpretation
434of nested formatting codes, meaning that the following four example lines are
435identical in meaning:
436
437 B<example: C<$a E<lt>=E<gt> $b>>
438
439 B<example: C<< $a <=> $b >>>
440
441 B<example: C<< $a E<lt>=E<gt> $b >>>
442
443 B<<< example: C<< $a E<lt>=E<gt> $b >> >>>
444
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445=back
446
447In parsing Pod, a notably tricky part is the correct parsing of
448(potentially nested!) formatting codes. Implementors should
449consult the code in the C<parse_text> routine in Pod::Parser as an
450example of a correct implementation.
451
452=over
453
454=item C<IE<lt>textE<gt>> -- italic text
455
456See the brief discussion in L<perlpod/"Formatting Codes">.
457
458=item C<BE<lt>textE<gt>> -- bold text
459
460See the brief discussion in L<perlpod/"Formatting Codes">.
461
462=item C<CE<lt>codeE<gt>> -- code text
463
464See the brief discussion in L<perlpod/"Formatting Codes">.
465
466=item C<FE<lt>filenameE<gt>> -- style for filenames
467
468See the brief discussion in L<perlpod/"Formatting Codes">.
469
470=item C<XE<lt>topic nameE<gt>> -- an index entry
471
472See the brief discussion in L<perlpod/"Formatting Codes">.
473
474This code is unusual in that most formatters completely discard
475this code and its content. Other formatters will render it with
476invisible codes that can be used in building an index of
477the current document.
478
479=item C<ZE<lt>E<gt>> -- a null (zero-effect) formatting code
480
481Discussed briefly in L<perlpod/"Formatting Codes">.
482
c195f169 483This code is unusual in that it should have no content. That is,
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484a processor may complain if it sees C<ZE<lt>potatoesE<gt>>. Whether
485or not it complains, the I<potatoes> text should ignored.
486
487=item C<LE<lt>nameE<gt>> -- a hyperlink
488
489The complicated syntaxes of this code are discussed at length in
490L<perlpod/"Formatting Codes">, and implementation details are
491discussed below, in L</"About LE<lt>...E<gt> Codes">. Parsing the
492contents of LE<lt>content> is tricky. Notably, the content has to be
493checked for whether it looks like a URL, or whether it has to be split
494on literal "|" and/or "/" (in the right order!), and so on,
495I<before> EE<lt>...> codes are resolved.
496
497=item C<EE<lt>escapeE<gt>> -- a character escape
498
499See L<perlpod/"Formatting Codes">, and several points in
500L</Notes on Implementing Pod Processors>.
501
502=item C<SE<lt>textE<gt>> -- text contains non-breaking spaces
503
504This formatting code is syntactically simple, but semantically
505complex. What it means is that each space in the printable
3e666715 506content of this code signifies a non-breaking space.
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507
508Consider:
509
510 C<$x ? $y : $z>
511
512 S<C<$x ? $y : $z>>
513
514Both signify the monospace (c[ode] style) text consisting of
515"$x", one space, "?", one space, ":", one space, "$z". The
516difference is that in the latter, with the S code, those spaces
3e666715 517are not "normal" spaces, but instead are non-breaking spaces.
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518
519=back
520
521
522If a Pod processor sees any formatting code other than the ones
523listed above (as in "NE<lt>...>", or "QE<lt>...>", etc.), that
524processor must by default treat this as an error.
525A Pod parser may allow a way for particular
526applications to add to the above list of known formatting codes;
527a Pod parser might even allow a way to stipulate, for each additional
528command, whether it requires some form of special processing, as
529LE<lt>...> does.
530
531Future versions of this specification may add additional
532formatting codes.
533
534Historical note: A few older Pod processors would not see a ">" as
535closing a "CE<lt>" code, if the ">" was immediately preceded by
536a "-". This was so that this:
537
538 C<$foo->bar>
539
540would parse as equivalent to this:
541
75f15e9f 542 C<$foo-E<gt>bar>
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543
544instead of as equivalent to a "C" formatting code containing
545only "$foo-", and then a "bar>" outside the "C" formatting code. This
546problem has since been solved by the addition of syntaxes like this:
547
548 C<< $foo->bar >>
549
550Compliant parsers must not treat "->" as special.
551
552Formatting codes absolutely cannot span paragraphs. If a code is
553opened in one paragraph, and no closing code is found by the end of
554that paragraph, the Pod parser must close that formatting code,
555and should complain (as in "Unterminated I code in the paragraph
556starting at line 123: 'Time objects are not...'"). So these
557two paragraphs:
558
559 I<I told you not to do this!
210b36aa 560
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561 Don't make me say it again!>
562
563...must I<not> be parsed as two paragraphs in italics (with the I
564code starting in one paragraph and starting in another.) Instead,
565the first paragraph should generate a warning, but that aside, the
566above code must parse as if it were:
567
568 I<I told you not to do this!>
210b36aa 569
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570 Don't make me say it again!E<gt>
571
572(In SGMLish jargon, all Pod commands are like block-level
573elements, whereas all Pod formatting codes are like inline-level
574elements.)
575
576
577
578=head1 Notes on Implementing Pod Processors
579
580The following is a long section of miscellaneous requirements
581and suggestions to do with Pod processing.
582
583=over
584
585=item *
586
587Pod formatters should tolerate lines in verbatim blocks that are of
588any length, even if that means having to break them (possibly several
589times, for very long lines) to avoid text running off the side of the
590page. Pod formatters may warn of such line-breaking. Such warnings
591are particularly appropriate for lines are over 100 characters long, which
592are usually not intentional.
593
594=item *
595
596Pod parsers must recognize I<all> of the three well-known newline
597formats: CR, LF, and CRLF. See L<perlport|perlport>.
598
599=item *
600
601Pod parsers should accept input lines that are of any length.
602
603=item *
604
605Since Perl recognizes a Unicode Byte Order Mark at the start of files
606as signaling that the file is Unicode encoded as in UTF-16 (whether
607big-endian or little-endian) or UTF-8, Pod parsers should do the
608same. Otherwise, the character encoding should be understood as
609being UTF-8 if the first highbit byte sequence in the file seems
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610valid as a UTF-8 sequence, or otherwise as CP-1252 (earlier versions of
611this specification used Latin-1 instead of CP-1252).
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612
613Future versions of this specification may specify
614how Pod can accept other encodings. Presumably treatment of other
615encodings in Pod parsing would be as in XML parsing: whatever the
616encoding declared by a particular Pod file, content is to be
617stored in memory as Unicode characters.
618
619=item *
620
621The well known Unicode Byte Order Marks are as follows: if the
622file begins with the two literal byte values 0xFE 0xFF, this is
623the BOM for big-endian UTF-16. If the file begins with the two
624literal byte value 0xFF 0xFE, this is the BOM for little-endian
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625UTF-16. On an ASCII platform, if the file begins with the three literal
626byte values
8a93676d 6270xEF 0xBB 0xBF, this is the BOM for UTF-8.
e8a0e562 628A mechanism portable to EBCDIC platforms is to:
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629
630 my $utf8_bom = "\x{FEFF}";
631 utf8::encode($utf8_bom);
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632
633=for comment
634 use bytes; print map sprintf(" 0x%02X", ord $_), split '', "\x{feff}";
635 0xEF 0xBB 0xBF
636
637=for comment
1e54db1a 638 If toke.c is modified to support UTF-32, add mention of those here.
8a93676d
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639
640=item *
641
df0c7995
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642A naive, but often sufficient heuristic on ASCII platforms, for testing
643the first highbit
8a93676d
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644byte-sequence in a BOM-less file (whether in code or in Pod!), to see
645whether that sequence is valid as UTF-8 (RFC 2279) is to check whether
9a5b9407 646that the first byte in the sequence is in the range 0xC2 - 0xFD
8a93676d
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647I<and> whether the next byte is in the range
6480x80 - 0xBF. If so, the parser may conclude that this file is in
649UTF-8, and all highbit sequences in the file should be assumed to
650be UTF-8. Otherwise the parser should treat the file as being
df0c7995
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651in CP-1252. (A better check, and which works on EBCDIC platforms as
652well, is to pass a copy of the sequence to
9a5b9407
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653L<utf8::decode()|utf8> which performs a full validity check on the
654sequence and returns TRUE if it is valid UTF-8, FALSE otherwise. This
655function is always pre-loaded, is fast because it is written in C, and
656will only get called at most once, so you don't need to avoid it out of
657performance concerns.)
658In the unlikely circumstance that the first highbit
8a93676d
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659sequence in a truly non-UTF-8 file happens to appear to be UTF-8, one
660can cater to our heuristic (as well as any more intelligent heuristic)
661by prefacing that line with a comment line containing a highbit
662sequence that is clearly I<not> valid as UTF-8. A line consisting
663of simply "#", an e-acute, and any non-highbit byte,
664is sufficient to establish this file's encoding.
665
666=for comment
667 If/WHEN some brave soul makes these heuristics into a generic
fae2c0fb 668 text-file class (or PerlIO layer?), we can presumably delete
8a93676d 669 mention of these icky details from this file, and can instead
fae2c0fb 670 tell people to just use appropriate class/layer.
8a93676d 671 Auto-recognition of newline sequences would be another desirable
fae2c0fb 672 feature of such a class/layer.
8a93676d
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673 HINT HINT HINT.
674
675=for comment
676 "The probability that a string of characters
677 in any other encoding appears as valid UTF-8 is low" - RFC2279
678
679=item *
680
8a93676d
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681Pod processors must treat a "=for [label] [content...]" paragraph as
682meaning the same thing as a "=begin [label]" paragraph, content, and
683an "=end [label]" paragraph. (The parser may conflate these two
684constructs, or may leave them distinct, in the expectation that the
685formatter will nevertheless treat them the same.)
686
687=item *
688
689When rendering Pod to a format that allows comments (i.e., to nearly
690any format other than plaintext), a Pod formatter must insert comment
691text identifying its name and version number, and the name and
692version numbers of any modules it might be using to process the Pod.
693Minimal examples:
694
555bd962 695 %% POD::Pod2PS v3.14159, using POD::Parser v1.92
210b36aa 696
555bd962 697 <!-- Pod::HTML v3.14159, using POD::Parser v1.92 -->
210b36aa 698
555bd962 699 {\doccomm generated by Pod::Tree::RTF 3.14159 using Pod::Tree 1.08}
210b36aa 700
555bd962 701 .\" Pod::Man version 3.14159, using POD::Parser version 1.92
8a93676d
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702
703Formatters may also insert additional comments, including: the
704release date of the Pod formatter program, the contact address for
705the author(s) of the formatter, the current time, the name of input
706file, the formatting options in effect, version of Perl used, etc.
707
708Formatters may also choose to note errors/warnings as comments,
709besides or instead of emitting them otherwise (as in messages to
710STDERR, or C<die>ing).
711
712=item *
713
714Pod parsers I<may> emit warnings or error messages ("Unknown E code
715EE<lt>zslig>!") to STDERR (whether through printing to STDERR, or
716C<warn>ing/C<carp>ing, or C<die>ing/C<croak>ing), but I<must> allow
717suppressing all such STDERR output, and instead allow an option for
718reporting errors/warnings
719in some other way, whether by triggering a callback, or noting errors
720in some attribute of the document object, or some similarly unobtrusive
721mechanism -- or even by appending a "Pod Errors" section to the end of
722the parsed form of the document.
723
724=item *
725
726In cases of exceptionally aberrant documents, Pod parsers may abort the
727parse. Even then, using C<die>ing/C<croak>ing is to be avoided; where
728possible, the parser library may simply close the input file
729and add text like "*** Formatting Aborted ***" to the end of the
730(partial) in-memory document.
731
732=item *
733
734In paragraphs where formatting codes (like EE<lt>...>, BE<lt>...>)
735are understood (i.e., I<not> verbatim paragraphs, but I<including>
736ordinary paragraphs, and command paragraphs that produce renderable
737text, like "=head1"), literal whitespace should generally be considered
738"insignificant", in that one literal space has the same meaning as any
739(nonzero) number of literal spaces, literal newlines, and literal tabs
740(as long as this produces no blank lines, since those would terminate
741the paragraph). Pod parsers should compact literal whitespace in each
742processed paragraph, but may provide an option for overriding this
743(since some processing tasks do not require it), or may follow
744additional special rules (for example, specially treating
745period-space-space or period-newline sequences).
746
747=item *
748
749Pod parsers should not, by default, try to coerce apostrophe (') and
750quote (") into smart quotes (little 9's, 66's, 99's, etc), nor try to
751turn backtick (`) into anything else but a single backtick character
353c6505 752(distinct from an open quote character!), nor "--" into anything but
8a93676d
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753two minus signs. They I<must never> do any of those things to text
754in CE<lt>...> formatting codes, and never I<ever> to text in verbatim
755paragraphs.
756
757=item *
758
759When rendering Pod to a format that has two kinds of hyphens (-), one
3e666715 760that's a non-breaking hyphen, and another that's a breakable hyphen
8a93676d
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761(as in "object-oriented", which can be split across lines as
762"object-", newline, "oriented"), formatters are encouraged to
3e666715 763generally translate "-" to non-breaking hyphen, but may apply
8a93676d
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764heuristics to convert some of these to breaking hyphens.
765
766=item *
767
768Pod formatters should make reasonable efforts to keep words of Perl
769code from being broken across lines. For example, "Foo::Bar" in some
770formatting systems is seen as eligible for being broken across lines
771as "Foo::" newline "Bar" or even "Foo::-" newline "Bar". This should
772be avoided where possible, either by disabling all line-breaking in
773mid-word, or by wrapping particular words with internal punctuation
774in "don't break this across lines" codes (which in some formats may
775not be a single code, but might be a matter of inserting non-breaking
776zero-width spaces between every pair of characters in a word.)
777
778=item *
779
780Pod parsers should, by default, expand tabs in verbatim paragraphs as
781they are processed, before passing them to the formatter or other
782processor. Parsers may also allow an option for overriding this.
783
784=item *
785
786Pod parsers should, by default, remove newlines from the end of
787ordinary and verbatim paragraphs before passing them to the
788formatter. For example, while the paragraph you're reading now
789could be considered, in Pod source, to end with (and contain)
790the newline(s) that end it, it should be processed as ending with
791(and containing) the period character that ends this sentence.
792
793=item *
794
795Pod parsers, when reporting errors, should make some effort to report
796an approximate line number ("Nested EE<lt>>'s in Paragraph #52, near
797line 633 of Thing/Foo.pm!"), instead of merely noting the paragraph
798number ("Nested EE<lt>>'s in Paragraph #52 of Thing/Foo.pm!"). Where
799this is problematic, the paragraph number should at least be
800accompanied by an excerpt from the paragraph ("Nested EE<lt>>'s in
801Paragraph #52 of Thing/Foo.pm, which begins 'Read/write accessor for
802the CE<lt>interest rate> attribute...'").
803
804=item *
805
806Pod parsers, when processing a series of verbatim paragraphs one
807after another, should consider them to be one large verbatim
808paragraph that happens to contain blank lines. I.e., these two
d1be9408 809lines, which have a blank line between them:
8a93676d
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810
811 use Foo;
812
813 print Foo->VERSION
814
815should be unified into one paragraph ("\tuse Foo;\n\n\tprint
816Foo->VERSION") before being passed to the formatter or other
817processor. Parsers may also allow an option for overriding this.
818
819While this might be too cumbersome to implement in event-based Pod
820parsers, it is straightforward for parsers that return parse trees.
821
822=item *
823
824Pod formatters, where feasible, are advised to avoid splitting short
825verbatim paragraphs (under twelve lines, say) across pages.
826
827=item *
828
829Pod parsers must treat a line with only spaces and/or tabs on it as a
830"blank line" such as separates paragraphs. (Some older parsers
831recognized only two adjacent newlines as a "blank line" but would not
832recognize a newline, a space, and a newline, as a blank line. This
833is noncompliant behavior.)
834
835=item *
836
837Authors of Pod formatters/processors should make every effort to
838avoid writing their own Pod parser. There are already several in
839CPAN, with a wide range of interface styles -- and one of them,
33874d2e 840Pod::Simple, comes with modern versions of Perl.
8a93676d
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841
842=item *
843
844Characters in Pod documents may be conveyed either as literals, or by
845number in EE<lt>n> codes, or by an equivalent mnemonic, as in
bd940430
KW
846EE<lt>eacute> which is exactly equivalent to EE<lt>233>. The numbers
847are the Latin1/Unicode values, even on EBCDIC platforms.
848
849When referring to characters by using a EE<lt>n> numeric code, numbers
850in the range 32-126 refer to those well known US-ASCII characters (also
851defined there by Unicode, with the same meaning), which all Pod
df0c7995
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852formatters must render faithfully. Characters whose EE<lt>E<gt> numbers
853are in the ranges 0-31 and 127-159 should not be used (neither as
854literals,
855nor as EE<lt>number> codes), except for the literal byte-sequences for
856newline (ASCII 13, ASCII 13 10, or ASCII 10), and tab (ASCII 9).
bd940430
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857
858Numbers in the range 160-255 refer to Latin-1 characters (also
859defined there by Unicode, with the same meaning). Numbers above
8a93676d
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860255 should be understood to refer to Unicode characters.
861
862=item *
863
864Be warned
865that some formatters cannot reliably render characters outside 32-126;
866and many are able to handle 32-126 and 160-255, but nothing above
867255.
868
869=item *
870
871Besides the well-known "EE<lt>lt>" and "EE<lt>gt>" codes for
872less-than and greater-than, Pod parsers must understand "EE<lt>sol>"
873for "/" (solidus, slash), and "EE<lt>verbar>" for "|" (vertical bar,
874pipe). Pod parsers should also understand "EE<lt>lchevron>" and
875"EE<lt>rchevron>" as legacy codes for characters 171 and 187, i.e.,
876"left-pointing double angle quotation mark" = "left pointing
877guillemet" and "right-pointing double angle quotation mark" = "right
878pointing guillemet". (These look like little "<<" and ">>", and they
879are now preferably expressed with the HTML/XHTML codes "EE<lt>laquo>"
880and "EE<lt>raquo>".)
881
882=item *
883
884Pod parsers should understand all "EE<lt>html>" codes as defined
885in the entity declarations in the most recent XHTML specification at
886C<www.W3.org>. Pod parsers must understand at least the entities
887that define characters in the range 160-255 (Latin-1). Pod parsers,
888when faced with some unknown "EE<lt>I<identifier>>" code,
889shouldn't simply replace it with nullstring (by default, at least),
890but may pass it through as a string consisting of the literal characters
891E, less-than, I<identifier>, greater-than. Or Pod parsers may offer the
892alternative option of processing such unknown
893"EE<lt>I<identifier>>" codes by firing an event especially
894for such codes, or by adding a special node-type to the in-memory
895document tree. Such "EE<lt>I<identifier>>" may have special meaning
896to some processors, or some processors may choose to add them to
897a special error report.
898
899=item *
900
901Pod parsers must also support the XHTML codes "EE<lt>quot>" for
902character 34 (doublequote, "), "EE<lt>amp>" for character 38
903(ampersand, &), and "EE<lt>apos>" for character 39 (apostrophe, ').
904
905=item *
906
1bca558f 907Note that in all cases of "EE<lt>whateverE<gt>", I<whatever> (whether
8a93676d 908an htmlname, or a number in any base) must consist only of
817141f8 909alphanumeric characters -- that is, I<whatever> must match
1bca558f 910C<m/\A\w+\z/>. So S<"EE<lt> 0 1 2 3 E<gt>"> is invalid, because
8a93676d
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911it contains spaces, which aren't alphanumeric characters. This
912presumably does not I<need> special treatment by a Pod processor;
1bca558f 913S<" 0 1 2 3 "> doesn't look like a number in any base, so it would
8a93676d 914presumably be looked up in the table of HTML-like names. Since
1bca558f 915there isn't (and cannot be) an HTML-like entity called S<" 0 1 2 3 ">,
8a93676d 916this will be treated as an error. However, Pod processors may
1bca558f 917treat S<"EE<lt> 0 1 2 3 E<gt>"> or "EE<lt>e-acute>" as I<syntactically>
8a93676d
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918invalid, potentially earning a different error message than the
919error message (or warning, or event) generated by a merely unknown
920(but theoretically valid) htmlname, as in "EE<lt>qacute>"
921[sic]. However, Pod parsers are not required to make this
922distinction.
923
924=item *
925
926Note that EE<lt>number> I<must not> be interpreted as simply
927"codepoint I<number> in the current/native character set". It always
928means only "the character represented by codepoint I<number> in
929Unicode." (This is identical to the semantics of &#I<number>; in XML.)
930
931This will likely require many formatters to have tables mapping from
932treatable Unicode codepoints (such as the "\xE9" for the e-acute
933character) to the escape sequences or codes necessary for conveying
934such sequences in the target output format. A converter to *roff
935would, for example know that "\xE9" (whether conveyed literally, or via
936a EE<lt>...> sequence) is to be conveyed as "e\\*'".
8939ba94 937Similarly, a program rendering Pod in a Mac OS application window, would
8a93676d 938presumably need to know that "\xE9" maps to codepoint 142 in MacRoman
8939ba94 939encoding that (at time of writing) is native for Mac OS. Such
8a93676d
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940Unicode2whatever mappings are presumably already widely available for
941common output formats. (Such mappings may be incomplete! Implementers
942are not expected to bend over backwards in an attempt to render
943Cherokee syllabics, Etruscan runes, Byzantine musical symbols, or any
944of the other weird things that Unicode can encode.) And
945if a Pod document uses a character not found in such a mapping, the
946formatter should consider it an unrenderable character.
947
948=item *
949
950If, surprisingly, the implementor of a Pod formatter can't find a
951satisfactory pre-existing table mapping from Unicode characters to
952escapes in the target format (e.g., a decent table of Unicode
953characters to *roff escapes), it will be necessary to build such a
954table. If you are in this circumstance, you should begin with the
955characters in the range 0x00A0 - 0x00FF, which is mostly the heavily
956used accented characters. Then proceed (as patience permits and
957fastidiousness compels) through the characters that the (X)HTML
958standards groups judged important enough to merit mnemonics
959for. These are declared in the (X)HTML specifications at the
960www.W3.org site. At time of writing (September 2001), the most recent
961entity declaration files are:
962
963 http://www.w3.org/TR/xhtml1/DTD/xhtml-lat1.ent
964 http://www.w3.org/TR/xhtml1/DTD/xhtml-special.ent
965 http://www.w3.org/TR/xhtml1/DTD/xhtml-symbol.ent
966
967Then you can progress through any remaining notable Unicode characters
968in the range 0x2000-0x204D (consult the character tables at
969www.unicode.org), and whatever else strikes your fancy. For example,
970in F<xhtml-symbol.ent>, there is the entry:
971
972 <!ENTITY infin "&#8734;"> <!-- infinity, U+221E ISOtech -->
973
974While the mapping "infin" to the character "\x{221E}" will (hopefully)
975have been already handled by the Pod parser, the presence of the
976character in this file means that it's reasonably important enough to
977include in a formatter's table that maps from notable Unicode characters
978to the codes necessary for rendering them. So for a Unicode-to-*roff
979mapping, for example, this would merit the entry:
980
981 "\x{221E}" => '\(in',
982
983It is eagerly hoped that in the future, increasing numbers of formats
984(and formatters) will support Unicode characters directly (as (X)HTML
985does with C<&infin;>, C<&#8734;>, or C<&#x221E;>), reducing the need
986for idiosyncratic mappings of Unicode-to-I<my_escapes>.
987
988=item *
989
353c6505 990It is up to individual Pod formatter to display good judgement when
8a93676d
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991confronted with an unrenderable character (which is distinct from an
992unknown EE<lt>thing> sequence that the parser couldn't resolve to
993anything, renderable or not). It is good practice to map Latin letters
994with diacritics (like "EE<lt>eacute>"/"EE<lt>233>") to the corresponding
995unaccented US-ASCII letters (like a simple character 101, "e"), but
210b36aa 996clearly this is often not feasible, and an unrenderable character may
8a93676d
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997be represented as "?", or the like. In attempting a sane fallback
998(as from EE<lt>233> to "e"), Pod formatters may use the
999%Latin1Code_to_fallback table in L<Pod::Escapes|Pod::Escapes>, or
1000L<Text::Unidecode|Text::Unidecode>, if available.
1001
1002For example, this Pod text:
1003
1004 magic is enabled if you set C<$Currency> to 'E<euro>'.
1005
1006may be rendered as:
1007"magic is enabled if you set C<$Currency> to 'I<?>'" or as
1008"magic is enabled if you set C<$Currency> to 'B<[euro]>'", or as
1009"magic is enabled if you set C<$Currency> to '[x20AC]', etc.
1010
1011A Pod formatter may also note, in a comment or warning, a list of what
1012unrenderable characters were encountered.
1013
1014=item *
1015
1016EE<lt>...> may freely appear in any formatting code (other than
1017in another EE<lt>...> or in an ZE<lt>>). That is, "XE<lt>The
1018EE<lt>euro>1,000,000 Solution>" is valid, as is "LE<lt>The
1019EE<lt>euro>1,000,000 Solution|Million::Euros>".
1020
1021=item *
1022
3e666715 1023Some Pod formatters output to formats that implement non-breaking
8a93676d 1024spaces as an individual character (which I'll call "NBSP"), and
3e666715 1025others output to formats that implement non-breaking spaces just as
8a93676d
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1026spaces wrapped in a "don't break this across lines" code. Note that
1027at the level of Pod, both sorts of codes can occur: Pod can contain a
1028NBSP character (whether as a literal, or as a "EE<lt>160>" or
1029"EE<lt>nbsp>" code); and Pod can contain "SE<lt>foo
1030IE<lt>barE<gt> baz>" codes, where "mere spaces" (character 32) in
3e666715 1031such codes are taken to represent non-breaking spaces. Pod
8a93676d
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1032parsers should consider supporting the optional parsing of "SE<lt>foo
1033IE<lt>barE<gt> baz>" as if it were
1034"fooI<NBSP>IE<lt>barE<gt>I<NBSP>baz", and, going the other way, the
1035optional parsing of groups of words joined by NBSP's as if each group
1036were in a SE<lt>...> code, so that formatters may use the
1037representation that maps best to what the output format demands.
1038
1039=item *
1040
210b36aa 1041Some processors may find that the C<SE<lt>...E<gt>> code is easiest to
8a93676d
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1042implement by replacing each space in the parse tree under the content
1043of the S, with an NBSP. But note: the replacement should apply I<not> to
1044spaces in I<all> text, but I<only> to spaces in I<printable> text. (This
1045distinction may or may not be evident in the particular tree/event
1046model implemented by the Pod parser.) For example, consider this
1047unusual case:
1048
1049 S<L</Autoloaded Functions>>
1050
1051This means that the space in the middle of the visible link text must
1052not be broken across lines. In other words, it's the same as this:
1053
1054 L<"AutoloadedE<160>Functions"/Autoloaded Functions>
1055
1056However, a misapplied space-to-NBSP replacement could (wrongly)
1057produce something equivalent to this:
1058
1059 L<"AutoloadedE<160>Functions"/AutoloadedE<160>Functions>
1060
1061...which is almost definitely not going to work as a hyperlink (assuming
1062this formatter outputs a format supporting hypertext).
1063
1064Formatters may choose to just not support the S format code,
1065especially in cases where the output format simply has no NBSP
1066character/code and no code for "don't break this stuff across lines".
1067
1068=item *
1069
1070Besides the NBSP character discussed above, implementors are reminded
1071of the existence of the other "special" character in Latin-1, the
210b36aa 1072"soft hyphen" character, also known as "discretionary hyphen",
8a93676d
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1073i.e. C<EE<lt>173E<gt>> = C<EE<lt>0xADE<gt>> =
1074C<EE<lt>shyE<gt>>). This character expresses an optional hyphenation
1075point. That is, it normally renders as nothing, but may render as a
1076"-" if a formatter breaks the word at that point. Pod formatters
1077should, as appropriate, do one of the following: 1) render this with
1078a code with the same meaning (e.g., "\-" in RTF), 2) pass it through
1079in the expectation that the formatter understands this character as
1080such, or 3) delete it.
1081
1082For example:
1083
1084 sigE<shy>action
1085 manuE<shy>script
1086 JarkE<shy>ko HieE<shy>taE<shy>nieE<shy>mi
1087
1088These signal to a formatter that if it is to hyphenate "sigaction"
1089or "manuscript", then it should be done as
1090"sig-I<[linebreak]>action" or "manu-I<[linebreak]>script"
1091(and if it doesn't hyphenate it, then the C<EE<lt>shyE<gt>> doesn't
1092show up at all). And if it is
1093to hyphenate "Jarkko" and/or "Hietaniemi", it can do
1094so only at the points where there is a C<EE<lt>shyE<gt>> code.
1095
1096In practice, it is anticipated that this character will not be used
1097often, but formatters should either support it, or delete it.
1098
1099=item *
1100
1101If you think that you want to add a new command to Pod (like, say, a
1102"=biblio" command), consider whether you could get the same
1103effect with a for or begin/end sequence: "=for biblio ..." or "=begin
1104biblio" ... "=end biblio". Pod processors that don't understand
1105"=for biblio", etc, will simply ignore it, whereas they may complain
1106loudly if they see "=biblio".
1107
1108=item *
1109
1110Throughout this document, "Pod" has been the preferred spelling for
1111the name of the documentation format. One may also use "POD" or
da75cd15 1112"pod". For the documentation that is (typically) in the Pod
8a93676d
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1113format, you may use "pod", or "Pod", or "POD". Understanding these
1114distinctions is useful; but obsessing over how to spell them, usually
1115is not.
1116
1117=back
1118
1119
1120
1121
1122
1123=head1 About LE<lt>...E<gt> Codes
1124
1125As you can tell from a glance at L<perlpod|perlpod>, the LE<lt>...>
1126code is the most complex of the Pod formatting codes. The points below
1127will hopefully clarify what it means and how processors should deal
1128with it.
1129
1130=over
1131
1132=item *
1133
1134In parsing an LE<lt>...> code, Pod parsers must distinguish at least
1135four attributes:
1136
1137=over
1138
1139=item First:
1140
1bca558f 1141The link-text. If there is none, this must be C<undef>. (E.g., in
8a93676d
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1142"LE<lt>Perl Functions|perlfunc>", the link-text is "Perl Functions".
1143In "LE<lt>Time::HiRes>" and even "LE<lt>|Time::HiRes>", there is no
1144link text. Note that link text may contain formatting.)
1145
1146=item Second:
1147
ac036724 1148The possibly inferred link-text; i.e., if there was no real link
8a93676d
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1149text, then this is the text that we'll infer in its place. (E.g., for
1150"LE<lt>Getopt::Std>", the inferred link text is "Getopt::Std".)
1151
1152=item Third:
1153
1bca558f 1154The name or URL, or C<undef> if none. (E.g., in "LE<lt>Perl
ac036724 1155Functions|perlfunc>", the name (also sometimes called the page)
1bca558f 1156is "perlfunc". In "LE<lt>/CAVEATS>", the name is C<undef>.)
8a93676d
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1157
1158=item Fourth:
1159
1bca558f 1160The section (AKA "item" in older perlpods), or C<undef> if none. E.g.,
f41e638c 1161in "LE<lt>Getopt::Std/DESCRIPTIONE<gt>", "DESCRIPTION" is the section. (Note
8a93676d
SB
1162that this is not the same as a manpage section like the "5" in "man 5
1163crontab". "Section Foo" in the Pod sense means the part of the text
6edf2346 1164that's introduced by the heading or item whose text is "Foo".)
8a93676d
SB
1165
1166=back
1167
1168Pod parsers may also note additional attributes including:
1169
1170=over
1171
1172=item Fifth:
1173
1174A flag for whether item 3 (if present) is a URL (like
1175"http://lists.perl.org" is), in which case there should be no section
1176attribute; a Pod name (like "perldoc" and "Getopt::Std" are); or
1177possibly a man page name (like "crontab(5)" is).
1178
1179=item Sixth:
1180
1181The raw original LE<lt>...> content, before text is split on
1182"|", "/", etc, and before EE<lt>...> codes are expanded.
1183
1184=back
1185
1186(The above were numbered only for concise reference below. It is not
1187a requirement that these be passed as an actual list or array.)
1188
1189For example:
1190
1191 L<Foo::Bar>
555bd962
BG
1192 => undef, # link text
1193 "Foo::Bar", # possibly inferred link text
1194 "Foo::Bar", # name
1195 undef, # section
1196 'pod', # what sort of link
1197 "Foo::Bar" # original content
8a93676d
SB
1198
1199 L<Perlport's section on NL's|perlport/Newlines>
555bd962
BG
1200 => "Perlport's section on NL's", # link text
1201 "Perlport's section on NL's", # possibly inferred link text
1202 "perlport", # name
1203 "Newlines", # section
1204 'pod', # what sort of link
1205 "Perlport's section on NL's|perlport/Newlines"
1206 # original content
8a93676d
SB
1207
1208 L<perlport/Newlines>
555bd962
BG
1209 => undef, # link text
1210 '"Newlines" in perlport', # possibly inferred link text
1211 "perlport", # name
1212 "Newlines", # section
1213 'pod', # what sort of link
1214 "perlport/Newlines" # original content
8a93676d
SB
1215
1216 L<crontab(5)/"DESCRIPTION">
555bd962
BG
1217 => undef, # link text
1218 '"DESCRIPTION" in crontab(5)', # possibly inferred link text
1219 "crontab(5)", # name
1220 "DESCRIPTION", # section
1221 'man', # what sort of link
1222 'crontab(5)/"DESCRIPTION"' # original content
8a93676d
SB
1223
1224 L</Object Attributes>
555bd962
BG
1225 => undef, # link text
1226 '"Object Attributes"', # possibly inferred link text
1227 undef, # name
1228 "Object Attributes", # section
1229 'pod', # what sort of link
1230 "/Object Attributes" # original content
8a93676d
SB
1231
1232 L<http://www.perl.org/>
555bd962
BG
1233 => undef, # link text
1234 "http://www.perl.org/", # possibly inferred link text
1235 "http://www.perl.org/", # name
1236 undef, # section
1237 'url', # what sort of link
1238 "http://www.perl.org/" # original content
8a93676d 1239
f6e963e4 1240 L<Perl.org|http://www.perl.org/>
555bd962
BG
1241 => "Perl.org", # link text
1242 "http://www.perl.org/", # possibly inferred link text
1243 "http://www.perl.org/", # name
1244 undef, # section
1245 'url', # what sort of link
f6e963e4
RS
1246 "Perl.org|http://www.perl.org/" # original content
1247
8a93676d
SB
1248Note that you can distinguish URL-links from anything else by the
1249fact that they match C<m/\A\w+:[^:\s]\S*\z/>. So
1250C<LE<lt>http://www.perl.comE<gt>> is a URL, but
1251C<LE<lt>HTTP::ResponseE<gt>> isn't.
1252
1253=item *
1254
1255In case of LE<lt>...> codes with no "text|" part in them,
1256older formatters have exhibited great variation in actually displaying
1257the link or cross reference. For example, LE<lt>crontab(5)> would render
1258as "the C<crontab(5)> manpage", or "in the C<crontab(5)> manpage"
1259or just "C<crontab(5)>".
1260
1261Pod processors must now treat "text|"-less links as follows:
1262
1263 L<name> => L<name|name>
1264 L</section> => L<"section"|/section>
1265 L<name/section> => L<"section" in name|name/section>
1266
1267=item *
1268
1269Note that section names might contain markup. I.e., if a section
1270starts with:
1271
1272 =head2 About the C<-M> Operator
1273
1274or with:
1275
1276 =item About the C<-M> Operator
1277
1278then a link to it would look like this:
1279
1280 L<somedoc/About the C<-M> Operator>
1281
1282Formatters may choose to ignore the markup for purposes of resolving
1283the link and use only the renderable characters in the section name,
1284as in:
1285
1286 <h1><a name="About_the_-M_Operator">About the <code>-M</code>
1287 Operator</h1>
210b36aa 1288
8a93676d 1289 ...
210b36aa 1290
8a93676d
SB
1291 <a href="somedoc#About_the_-M_Operator">About the <code>-M</code>
1292 Operator" in somedoc</a>
1293
1294=item *
1295
1296Previous versions of perlpod distinguished C<LE<lt>name/"section"E<gt>>
1297links from C<LE<lt>name/itemE<gt>> links (and their targets). These
1298have been merged syntactically and semantically in the current
1299specification, and I<section> can refer either to a "=headI<n> Heading
1300Content" command or to a "=item Item Content" command. This
1301specification does not specify what behavior should be in the case
1302of a given document having several things all seeming to produce the
1303same I<section> identifier (e.g., in HTML, several things all producing
1304the same I<anchorname> in <a name="I<anchorname>">...</a>
1305elements). Where Pod processors can control this behavior, they should
1306use the first such anchor. That is, C<LE<lt>Foo/BarE<gt>> refers to the
1307I<first> "Bar" section in Foo.
1308
1309But for some processors/formats this cannot be easily controlled; as
1310with the HTML example, the behavior of multiple ambiguous
1311<a name="I<anchorname>">...</a> is most easily just left up to
1312browsers to decide.
1313
1314=item *
1315
8a93676d
SB
1316In a C<LE<lt>text|...E<gt>> code, text may contain formatting codes
1317for formatting or for EE<lt>...> escapes, as in:
1318
1319 L<B<ummE<234>stuff>|...>
1320
1321For C<LE<lt>...E<gt>> codes without a "name|" part, only
ac036724 1322C<EE<lt>...E<gt>> and C<ZE<lt>E<gt>> codes may occur. That is,
1323authors should not use "C<LE<lt>BE<lt>Foo::BarE<gt>E<gt>>".
8a93676d
SB
1324
1325Note, however, that formatting codes and ZE<lt>>'s can occur in any
1326and all parts of an LE<lt>...> (i.e., in I<name>, I<section>, I<text>,
1327and I<url>).
1328
1329Authors must not nest LE<lt>...> codes. For example, "LE<lt>The
1330LE<lt>Foo::Bar> man page>" should be treated as an error.
1331
1332=item *
1333
1334Note that Pod authors may use formatting codes inside the "text"
1335part of "LE<lt>text|name>" (and so on for LE<lt>text|/"sec">).
1336
1337In other words, this is valid:
1338
1339 Go read L<the docs on C<$.>|perlvar/"$.">
1340
1341Some output formats that do allow rendering "LE<lt>...>" codes as
1342hypertext, might not allow the link-text to be formatted; in
1343that case, formatters will have to just ignore that formatting.
1344
1345=item *
1346
1347At time of writing, C<LE<lt>nameE<gt>> values are of two types:
1348either the name of a Pod page like C<LE<lt>Foo::BarE<gt>> (which
1349might be a real Perl module or program in an @INC / PATH
e1020413 1350directory, or a .pod file in those places); or the name of a Unix
8a93676d 1351man page, like C<LE<lt>crontab(5)E<gt>>. In theory, C<LE<lt>chmodE<gt>>
62a78fcb 1352is ambiguous between a Pod page called "chmod", or the Unix man page
8a93676d
SB
1353"chmod" (in whatever man-section). However, the presence of a string
1354in parens, as in "crontab(5)", is sufficient to signal that what
1355is being discussed is not a Pod page, and so is presumably a
e1020413 1356Unix man page. The distinction is of no importance to many
8a93676d
SB
1357Pod processors, but some processors that render to hypertext formats
1358may need to distinguish them in order to know how to render a
1359given C<LE<lt>fooE<gt>> code.
1360
1361=item *
1362
b41aadf2
RS
1363Previous versions of perlpod allowed for a C<LE<lt>sectionE<gt>> syntax (as in
1364C<LE<lt>Object AttributesE<gt>>), which was not easily distinguishable from
1365C<LE<lt>nameE<gt>> syntax and for C<LE<lt>"section"E<gt>> which was only
1366slightly less ambiguous. This syntax is no longer in the specification, and
1367has been replaced by the C<LE<lt>/sectionE<gt>> syntax (where the slash was
1368formerly optional). Pod parsers should tolerate the C<LE<lt>"section"E<gt>>
1369syntax, for a while at least. The suggested heuristic for distinguishing
1370C<LE<lt>sectionE<gt>> from C<LE<lt>nameE<gt>> is that if it contains any
1371whitespace, it's a I<section>. Pod processors should warn about this being
1372deprecated syntax.
8a93676d
SB
1373
1374=back
1375
1376=head1 About =over...=back Regions
1377
1378"=over"..."=back" regions are used for various kinds of list-like
1379structures. (I use the term "region" here simply as a collective
1380term for everything from the "=over" to the matching "=back".)
1381
1382=over
1383
1384=item *
1385
1386The non-zero numeric I<indentlevel> in "=over I<indentlevel>" ...
1387"=back" is used for giving the formatter a clue as to how many
1388"spaces" (ems, or roughly equivalent units) it should tab over,
1389although many formatters will have to convert this to an absolute
1390measurement that may not exactly match with the size of spaces (or M's)
1391in the document's base font. Other formatters may have to completely
1392ignore the number. The lack of any explicit I<indentlevel> parameter is
1393equivalent to an I<indentlevel> value of 4. Pod processors may
1394complain if I<indentlevel> is present but is not a positive number
1395matching C<m/\A(\d*\.)?\d+\z/>.
1396
1397=item *
1398
1399Authors of Pod formatters are reminded that "=over" ... "=back" may
1400map to several different constructs in your output format. For
1401example, in converting Pod to (X)HTML, it can map to any of
1402<ul>...</ul>, <ol>...</ol>, <dl>...</dl>, or
1403<blockquote>...</blockquote>. Similarly, "=item" can map to <li> or
1404<dt>.
1405
1406=item *
1407
1408Each "=over" ... "=back" region should be one of the following:
1409
1410=over
1411
1412=item *
1413
1414An "=over" ... "=back" region containing only "=item *" commands,
1415each followed by some number of ordinary/verbatim paragraphs, other
1416nested "=over" ... "=back" regions, "=for..." paragraphs, and
1417"=begin"..."=end" regions.
1418
1419(Pod processors must tolerate a bare "=item" as if it were "=item
1420*".) Whether "*" is rendered as a literal asterisk, an "o", or as
1421some kind of real bullet character, is left up to the Pod formatter,
1422and may depend on the level of nesting.
1423
1424=item *
1425
1426An "=over" ... "=back" region containing only
1427C<m/\A=item\s+\d+\.?\s*\z/> paragraphs, each one (or each group of them)
1428followed by some number of ordinary/verbatim paragraphs, other nested
1429"=over" ... "=back" regions, "=for..." paragraphs, and/or
1430"=begin"..."=end" codes. Note that the numbers must start at 1
1431in each section, and must proceed in order and without skipping
1432numbers.
1433
1434(Pod processors must tolerate lines like "=item 1" as if they were
1435"=item 1.", with the period.)
1436
1437=item *
1438
1439An "=over" ... "=back" region containing only "=item [text]"
1440commands, each one (or each group of them) followed by some number of
1441ordinary/verbatim paragraphs, other nested "=over" ... "=back"
1442regions, or "=for..." paragraphs, and "=begin"..."=end" regions.
1443
1444The "=item [text]" paragraph should not match
1445C<m/\A=item\s+\d+\.?\s*\z/> or C<m/\A=item\s+\*\s*\z/>, nor should it
1446match just C<m/\A=item\s*\z/>.
1447
1448=item *
1449
1450An "=over" ... "=back" region containing no "=item" paragraphs at
1451all, and containing only some number of
1452ordinary/verbatim paragraphs, and possibly also some nested "=over"
1453... "=back" regions, "=for..." paragraphs, and "=begin"..."=end"
1454regions. Such an itemless "=over" ... "=back" region in Pod is
1455equivalent in meaning to a "<blockquote>...</blockquote>" element in
1456HTML.
1457
1458=back
1459
1460Note that with all the above cases, you can determine which type of
1461"=over" ... "=back" you have, by examining the first (non-"=cut",
1462non-"=pod") Pod paragraph after the "=over" command.
1463
1464=item *
1465
1466Pod formatters I<must> tolerate arbitrarily large amounts of text
1467in the "=item I<text...>" paragraph. In practice, most such
1468paragraphs are short, as in:
1469
1470 =item For cutting off our trade with all parts of the world
1471
1472But they may be arbitrarily long:
1473
1474 =item For transporting us beyond seas to be tried for pretended
1475 offenses
1476
1477 =item He is at this time transporting large armies of foreign
1478 mercenaries to complete the works of death, desolation and
1479 tyranny, already begun with circumstances of cruelty and perfidy
1480 scarcely paralleled in the most barbarous ages, and totally
1481 unworthy the head of a civilized nation.
1482
1483=item *
1484
1485Pod processors should tolerate "=item *" / "=item I<number>" commands
1486with no accompanying paragraph. The middle item is an example:
1487
1488 =over
210b36aa 1489
8a93676d 1490 =item 1
210b36aa 1491
8a93676d 1492 Pick up dry cleaning.
210b36aa 1493
8a93676d 1494 =item 2
210b36aa 1495
8a93676d 1496 =item 3
210b36aa 1497
8a93676d 1498 Stop by the store. Get Abba Zabas, Stoli, and cheap lawn chairs.
210b36aa 1499
8a93676d
SB
1500 =back
1501
1502=item *
1503
1504No "=over" ... "=back" region can contain headings. Processors may
1505treat such a heading as an error.
1506
1507=item *
1508
1509Note that an "=over" ... "=back" region should have some
1510content. That is, authors should not have an empty region like this:
1511
1512 =over
210b36aa 1513
8a93676d
SB
1514 =back
1515
1516Pod processors seeing such a contentless "=over" ... "=back" region,
1517may ignore it, or may report it as an error.
1518
1519=item *
1520
1521Processors must tolerate an "=over" list that goes off the end of the
1522document (i.e., which has no matching "=back"), but they may warn
1523about such a list.
1524
1525=item *
1526
1527Authors of Pod formatters should note that this construct:
1528
1529 =item Neque
1530
1531 =item Porro
1532
1533 =item Quisquam Est
210b36aa 1534
8a93676d
SB
1535 Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci
1536 velit, sed quia non numquam eius modi tempora incidunt ut
1537 labore et dolore magnam aliquam quaerat voluptatem.
1538
1539 =item Ut Enim
1540
1541is semantically ambiguous, in a way that makes formatting decisions
1542a bit difficult. On the one hand, it could be mention of an item
1543"Neque", mention of another item "Porro", and mention of another
1544item "Quisquam Est", with just the last one requiring the explanatory
1545paragraph "Qui dolorem ipsum quia dolor..."; and then an item
1546"Ut Enim". In that case, you'd want to format it like so:
1547
1548 Neque
210b36aa 1549
8a93676d 1550 Porro
210b36aa 1551
8a93676d
SB
1552 Quisquam Est
1553 Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci
1554 velit, sed quia non numquam eius modi tempora incidunt ut
1555 labore et dolore magnam aliquam quaerat voluptatem.
1556
1557 Ut Enim
1558
1559But it could equally well be a discussion of three (related or equivalent)
1560items, "Neque", "Porro", and "Quisquam Est", followed by a paragraph
1561explaining them all, and then a new item "Ut Enim". In that case, you'd
1562probably want to format it like so:
1563
1564 Neque
1565 Porro
1566 Quisquam Est
1567 Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci
1568 velit, sed quia non numquam eius modi tempora incidunt ut
1569 labore et dolore magnam aliquam quaerat voluptatem.
1570
1571 Ut Enim
1572
353c6505 1573But (for the foreseeable future), Pod does not provide any way for Pod
8a93676d
SB
1574authors to distinguish which grouping is meant by the above
1575"=item"-cluster structure. So formatters should format it like so:
1576
1577 Neque
1578
1579 Porro
1580
1581 Quisquam Est
1582
1583 Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci
1584 velit, sed quia non numquam eius modi tempora incidunt ut
1585 labore et dolore magnam aliquam quaerat voluptatem.
1586
1587 Ut Enim
1588
210b36aa 1589That is, there should be (at least roughly) equal spacing between
8a93676d
SB
1590items as between paragraphs (although that spacing may well be less
1591than the full height of a line of text). This leaves it to the reader
1592to use (con)textual cues to figure out whether the "Qui dolorem
1593ipsum..." paragraph applies to the "Quisquam Est" item or to all three
1594items "Neque", "Porro", and "Quisquam Est". While not an ideal
1595situation, this is preferable to providing formatting cues that may
1596be actually contrary to the author's intent.
1597
1598=back
1599
1600
1601
1602=head1 About Data Paragraphs and "=begin/=end" Regions
1603
1604Data paragraphs are typically used for inlining non-Pod data that is
1605to be used (typically passed through) when rendering the document to
1606a specific format:
1607
1608 =begin rtf
210b36aa 1609
8a93676d 1610 \par{\pard\qr\sa4500{\i Printed\~\chdate\~\chtime}\par}
210b36aa 1611
8a93676d
SB
1612 =end rtf
1613
1614The exact same effect could, incidentally, be achieved with a single
1615"=for" paragraph:
1616
1617 =for rtf \par{\pard\qr\sa4500{\i Printed\~\chdate\~\chtime}\par}
1618
1619(Although that is not formally a data paragraph, it has the same
1620meaning as one, and Pod parsers may parse it as one.)
1621
1622Another example of a data paragraph:
1623
1624 =begin html
210b36aa 1625
8a93676d 1626 I like <em>PIE</em>!
210b36aa 1627
8a93676d 1628 <hr>Especially pecan pie!
210b36aa 1629
8a93676d
SB
1630 =end html
1631
1632If these were ordinary paragraphs, the Pod parser would try to
1633expand the "EE<lt>/em>" (in the first paragraph) as a formatting
1634code, just like "EE<lt>lt>" or "EE<lt>eacute>". But since this
1635is in a "=begin I<identifier>"..."=end I<identifier>" region I<and>
1636the identifier "html" doesn't begin have a ":" prefix, the contents
1637of this region are stored as data paragraphs, instead of being
1638processed as ordinary paragraphs (or if they began with a spaces
1639and/or tabs, as verbatim paragraphs).
1640
1641As a further example: At time of writing, no "biblio" identifier is
1642supported, but suppose some processor were written to recognize it as
1643a way of (say) denoting a bibliographic reference (necessarily
1644containing formatting codes in ordinary paragraphs). The fact that
1645"biblio" paragraphs were meant for ordinary processing would be
1646indicated by prefacing each "biblio" identifier with a colon:
1647
1648 =begin :biblio
1649
1650 Wirth, Niklaus. 1976. I<Algorithms + Data Structures =
1651 Programs.> Prentice-Hall, Englewood Cliffs, NJ.
1652
1653 =end :biblio
1654
1655This would signal to the parser that paragraphs in this begin...end
1656region are subject to normal handling as ordinary/verbatim paragraphs
1657(while still tagged as meant only for processors that understand the
1658"biblio" identifier). The same effect could be had with:
1659
1660 =for :biblio
1661 Wirth, Niklaus. 1976. I<Algorithms + Data Structures =
1662 Programs.> Prentice-Hall, Englewood Cliffs, NJ.
1663
1664The ":" on these identifiers means simply "process this stuff
1665normally, even though the result will be for some special target".
1666I suggest that parser APIs report "biblio" as the target identifier,
1667but also report that it had a ":" prefix. (And similarly, with the
1668above "html", report "html" as the target identifier, and note the
1669I<lack> of a ":" prefix.)
1670
1671Note that a "=begin I<identifier>"..."=end I<identifier>" region where
1672I<identifier> begins with a colon, I<can> contain commands. For example:
1673
1674 =begin :biblio
210b36aa 1675
8a93676d 1676 Wirth's classic is available in several editions, including:
210b36aa 1677
8a93676d
SB
1678 =for comment
1679 hm, check abebooks.com for how much used copies cost.
210b36aa 1680
8a93676d 1681 =over
210b36aa 1682
8a93676d 1683 =item
210b36aa 1684
8a93676d
SB
1685 Wirth, Niklaus. 1975. I<Algorithmen und Datenstrukturen.>
1686 Teubner, Stuttgart. [Yes, it's in German.]
210b36aa 1687
8a93676d 1688 =item
210b36aa 1689
8a93676d
SB
1690 Wirth, Niklaus. 1976. I<Algorithms + Data Structures =
1691 Programs.> Prentice-Hall, Englewood Cliffs, NJ.
210b36aa 1692
8a93676d 1693 =back
210b36aa 1694
8a93676d
SB
1695 =end :biblio
1696
1697Note, however, a "=begin I<identifier>"..."=end I<identifier>"
1698region where I<identifier> does I<not> begin with a colon, should not
1699directly contain "=head1" ... "=head4" commands, nor "=over", nor "=back",
1700nor "=item". For example, this may be considered invalid:
1701
1702 =begin somedata
210b36aa 1703
8a93676d 1704 This is a data paragraph.
210b36aa 1705
8a93676d 1706 =head1 Don't do this!
210b36aa 1707
8a93676d 1708 This is a data paragraph too.
210b36aa 1709
8a93676d
SB
1710 =end somedata
1711
1712A Pod processor may signal that the above (specifically the "=head1"
1713paragraph) is an error. Note, however, that the following should
1714I<not> be treated as an error:
1715
1716 =begin somedata
210b36aa 1717
8a93676d 1718 This is a data paragraph.
210b36aa 1719
8a93676d 1720 =cut
210b36aa 1721
8a93676d
SB
1722 # Yup, this isn't Pod anymore.
1723 sub excl { (rand() > .5) ? "hoo!" : "hah!" }
210b36aa 1724
8a93676d 1725 =pod
210b36aa 1726
8a93676d 1727 This is a data paragraph too.
210b36aa 1728
8a93676d
SB
1729 =end somedata
1730
1731And this too is valid:
1732
1733 =begin someformat
210b36aa 1734
8a93676d 1735 This is a data paragraph.
210b36aa 1736
8a93676d 1737 And this is a data paragraph.
210b36aa 1738
8a93676d 1739 =begin someotherformat
210b36aa 1740
8a93676d 1741 This is a data paragraph too.
210b36aa 1742
8a93676d 1743 And this is a data paragraph too.
210b36aa 1744
8a93676d
SB
1745 =begin :yetanotherformat
1746
1747 =head2 This is a command paragraph!
1748
1749 This is an ordinary paragraph!
210b36aa 1750
8a93676d 1751 And this is a verbatim paragraph!
210b36aa 1752
8a93676d 1753 =end :yetanotherformat
210b36aa 1754
8a93676d 1755 =end someotherformat
210b36aa 1756
8a93676d 1757 Another data paragraph!
210b36aa 1758
8a93676d
SB
1759 =end someformat
1760
1761The contents of the above "=begin :yetanotherformat" ...
1762"=end :yetanotherformat" region I<aren't> data paragraphs, because
1763the immediately containing region's identifier (":yetanotherformat")
1764begins with a colon. In practice, most regions that contain
1765data paragraphs will contain I<only> data paragraphs; however,
1766the above nesting is syntactically valid as Pod, even if it is
1767rare. However, the handlers for some formats, like "html",
1768will accept only data paragraphs, not nested regions; and they may
1769complain if they see (targeted for them) nested regions, or commands,
1770other than "=end", "=pod", and "=cut".
1771
1772Also consider this valid structure:
1773
1774 =begin :biblio
210b36aa 1775
8a93676d 1776 Wirth's classic is available in several editions, including:
210b36aa 1777
8a93676d 1778 =over
210b36aa 1779
8a93676d 1780 =item
210b36aa 1781
8a93676d
SB
1782 Wirth, Niklaus. 1975. I<Algorithmen und Datenstrukturen.>
1783 Teubner, Stuttgart. [Yes, it's in German.]
210b36aa 1784
8a93676d 1785 =item
210b36aa 1786
8a93676d
SB
1787 Wirth, Niklaus. 1976. I<Algorithms + Data Structures =
1788 Programs.> Prentice-Hall, Englewood Cliffs, NJ.
1789
1790 =back
210b36aa 1791
8a93676d 1792 Buy buy buy!
210b36aa 1793
8a93676d 1794 =begin html
210b36aa 1795
8a93676d 1796 <img src='wirth_spokesmodeling_book.png'>
210b36aa 1797
8a93676d 1798 <hr>
210b36aa 1799
8a93676d 1800 =end html
210b36aa 1801
8a93676d 1802 Now now now!
210b36aa 1803
8a93676d
SB
1804 =end :biblio
1805
1806There, the "=begin html"..."=end html" region is nested inside
1807the larger "=begin :biblio"..."=end :biblio" region. Note that the
1808content of the "=begin html"..."=end html" region is data
1809paragraph(s), because the immediately containing region's identifier
1810("html") I<doesn't> begin with a colon.
1811
1812Pod parsers, when processing a series of data paragraphs one
1813after another (within a single region), should consider them to
1814be one large data paragraph that happens to contain blank lines. So
1815the content of the above "=begin html"..."=end html" I<may> be stored
1816as two data paragraphs (one consisting of
1817"<img src='wirth_spokesmodeling_book.png'>\n"
1818and another consisting of "<hr>\n"), but I<should> be stored as
1819a single data paragraph (consisting of
1820"<img src='wirth_spokesmodeling_book.png'>\n\n<hr>\n").
1821
1822Pod processors should tolerate empty
1823"=begin I<something>"..."=end I<something>" regions,
1824empty "=begin :I<something>"..."=end :I<something>" regions, and
1825contentless "=for I<something>" and "=for :I<something>"
1826paragraphs. I.e., these should be tolerated:
1827
1828 =for html
210b36aa 1829
8a93676d 1830 =begin html
210b36aa 1831
8a93676d 1832 =end html
210b36aa 1833
8a93676d 1834 =begin :biblio
210b36aa 1835
8a93676d
SB
1836 =end :biblio
1837
1838Incidentally, note that there's no easy way to express a data
1839paragraph starting with something that looks like a command. Consider:
1840
1841 =begin stuff
210b36aa 1842
8a93676d 1843 =shazbot
210b36aa 1844
8a93676d
SB
1845 =end stuff
1846
1847There, "=shazbot" will be parsed as a Pod command "shazbot", not as a data
1848paragraph "=shazbot\n". However, you can express a data paragraph consisting
1849of "=shazbot\n" using this code:
1850
1851 =for stuff =shazbot
1852
1853The situation where this is necessary, is presumably quite rare.
1854
1855Note that =end commands must match the currently open =begin command. That
1856is, they must properly nest. For example, this is valid:
1857
1858 =begin outer
210b36aa 1859
8a93676d 1860 X
210b36aa 1861
8a93676d 1862 =begin inner
210b36aa 1863
8a93676d 1864 Y
210b36aa 1865
8a93676d 1866 =end inner
210b36aa 1867
8a93676d 1868 Z
210b36aa 1869
8a93676d
SB
1870 =end outer
1871
1872while this is invalid:
1873
1874 =begin outer
210b36aa 1875
8a93676d 1876 X
210b36aa 1877
8a93676d 1878 =begin inner
210b36aa 1879
8a93676d 1880 Y
210b36aa 1881
8a93676d 1882 =end outer
210b36aa 1883
8a93676d 1884 Z
210b36aa 1885
8a93676d 1886 =end inner
210b36aa 1887
8a93676d
SB
1888This latter is improper because when the "=end outer" command is seen, the
1889currently open region has the formatname "inner", not "outer". (It just
1890happens that "outer" is the format name of a higher-up region.) This is
1891an error. Processors must by default report this as an error, and may halt
210b36aa 1892processing the document containing that error. A corollary of this is that
ac036724 1893regions cannot "overlap". That is, the latter block above does not represent
8a93676d
SB
1894a region called "outer" which contains X and Y, overlapping a region called
1895"inner" which contains Y and Z. But because it is invalid (as all
1896apparently overlapping regions would be), it doesn't represent that, or
1897anything at all.
1898
1899Similarly, this is invalid:
1900
1901 =begin thing
210b36aa 1902
8a93676d
SB
1903 =end hting
1904
1905This is an error because the region is opened by "thing", and the "=end"
1906tries to close "hting" [sic].
1907
1908This is also invalid:
1909
1910 =begin thing
210b36aa 1911
8a93676d
SB
1912 =end
1913
1914This is invalid because every "=end" command must have a formatname
1915parameter.
1916
1917=head1 SEE ALSO
1918
1919L<perlpod>, L<perlsyn/"PODs: Embedded Documentation">,
1920L<podchecker>
1921
1922=head1 AUTHOR
1923
1924Sean M. Burke
1925
1926=cut
1927
1928