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2 | =head1 NAME | |
3 | ||
4 | perlpodspec - Plain Old Documentation: format specification and notes | |
5 | ||
6 | =head1 DESCRIPTION | |
7 | ||
8 | This document is detailed notes on the Pod markup language. Most | |
9 | people will only have to read L<perlpod|perlpod> to know how to write | |
10 | in Pod, but this document may answer some incidental questions to do | |
11 | with parsing and rendering Pod. | |
12 | ||
13 | In this document, "must" / "must not", "should" / | |
14 | "should not", and "may" have their conventional (cf. RFC 2119) | |
15 | meanings: "X must do Y" means that if X doesn't do Y, it's against | |
16 | this specification, and should really be fixed. "X should do Y" | |
17 | means that it's recommended, but X may fail to do Y, if there's a | |
18 | good reason. "X may do Y" is merely a note that X can do Y at | |
19 | will (although it is up to the reader to detect any connotation of | |
20 | "and I think it would be I<nice> if X did Y" versus "it wouldn't | |
21 | really I<bother> me if X did Y"). | |
22 | ||
23 | Notably, when I say "the parser should do Y", the | |
24 | parser may fail to do Y, if the calling application explicitly | |
25 | requests that the parser I<not> do Y. I often phrase this as | |
26 | "the parser should, by default, do Y." This doesn't I<require> | |
27 | the parser to provide an option for turning off whatever | |
28 | feature Y is (like expanding tabs in verbatim paragraphs), although | |
29 | it implicates that such an option I<may> be provided. | |
30 | ||
31 | =head1 Pod Definitions | |
32 | ||
33 | Pod is embedded in files, typically Perl source files -- although you | |
34 | can write a file that's nothing but Pod. | |
35 | ||
36 | A B<line> in a file consists of zero or more non-newline characters, | |
37 | terminated by either a newline or the end of the file. | |
38 | ||
39 | A B<newline sequence> is usually a platform-dependent concept, but | |
40 | Pod parsers should understand it to mean any of CR (ASCII 13), LF | |
41 | (ASCII 10), or a CRLF (ASCII 13 followed immediately by ASCII 10), in | |
42 | addition to any other system-specific meaning. The first CR/CRLF/LF | |
43 | sequence in the file may be used as the basis for identifying the | |
44 | newline sequence for parsing the rest of the file. | |
45 | ||
46 | A B<blank line> is a line consisting entirely of zero or more spaces | |
47 | (ASCII 32) or tabs (ASCII 9), and terminated by a newline or end-of-file. | |
48 | A B<non-blank line> is a line containing one or more characters other | |
49 | than space or tab (and terminated by a newline or end-of-file). | |
50 | ||
51 | (I<Note:> Many older Pod parsers did not accept a line consisting of | |
52 | spaces/tabs and then a newline as a blank line -- the only lines they | |
53 | considered blank were lines consisting of I<no characters at all>, | |
54 | terminated by a newline.) | |
55 | ||
56 | B<Whitespace> is used in this document as a blanket term for spaces, | |
57 | tabs, and newline sequences. (By itself, this term usually refers | |
58 | to literal whitespace. That is, sequences of whitespace characters | |
59 | in Pod source, as opposed to "EE<lt>32>", which is a formatting | |
60 | code that I<denotes> a whitespace character.) | |
61 | ||
62 | A B<Pod parser> is a module meant for parsing Pod (regardless of | |
63 | whether this involves calling callbacks or building a parse tree or | |
64 | directly formatting it). A B<Pod formatter> (or B<Pod translator>) | |
65 | is a module or program that converts Pod to some other format (HTML, | |
66 | plaintext, TeX, PostScript, RTF). A B<Pod processor> might be a | |
67 | formatter or translator, or might be a program that does something | |
68 | else with the Pod (like wordcounting it, scanning for index points, | |
69 | etc.). | |
70 | ||
71 | Pod content is contained in B<Pod blocks>. A Pod block starts with a | |
72 | line that matches <m/\A=[a-zA-Z]/>, and continues up to the next line | |
73 | that matches C<m/\A=cut/> -- or up to the end of the file, if there is | |
74 | no C<m/\A=cut/> line. | |
75 | ||
76 | =for comment | |
77 | The current perlsyn says: | |
78 | [beginquote] | |
79 | Note that pod translators should look at only paragraphs beginning | |
80 | with a pod directive (it makes parsing easier), whereas the compiler | |
81 | actually knows to look for pod escapes even in the middle of a | |
82 | paragraph. This means that the following secret stuff will be ignored | |
83 | by both the compiler and the translators. | |
84 | $a=3; | |
85 | =secret stuff | |
86 | warn "Neither POD nor CODE!?" | |
87 | =cut back | |
88 | print "got $a\n"; | |
89 | You probably shouldn't rely upon the warn() being podded out forever. | |
90 | Not all pod translators are well-behaved in this regard, and perhaps | |
91 | the compiler will become pickier. | |
92 | [endquote] | |
93 | I think that those paragraphs should just be removed; paragraph-based | |
94 | parsing seems to have been largely abandoned, because of the hassle | |
95 | with non-empty blank lines messing up what people meant by "paragraph". | |
96 | Even if the "it makes parsing easier" bit were especially true, | |
97 | it wouldn't be worth the confusion of having perl and pod2whatever | |
98 | actually disagree on what can constitute a Pod block. | |
99 | ||
100 | Within a Pod block, there are B<Pod paragraphs>. A Pod paragraph | |
101 | consists of non-blank lines of text, separated by one or more blank | |
102 | lines. | |
103 | ||
104 | For purposes of Pod processing, there are four types of paragraphs in | |
105 | a Pod block: | |
106 | ||
107 | =over | |
108 | ||
109 | =item * | |
110 | ||
111 | A command paragraph (also called a "directive"). The first line of | |
112 | this paragraph must match C<m/\A=[a-zA-Z]/>. Command paragraphs are | |
113 | typically one line, as in: | |
114 | ||
115 | =head1 NOTES | |
116 | ||
117 | =item * | |
118 | ||
119 | But they may span several (non-blank) lines: | |
120 | ||
121 | =for comment | |
122 | Hm, I wonder what it would look like if | |
123 | you tried to write a BNF for Pod from this. | |
210b36aa | 124 | |
8a93676d SB |
125 | =head3 Dr. Strangelove, or: How I Learned to |
126 | Stop Worrying and Love the Bomb | |
127 | ||
128 | I<Some> command paragraphs allow formatting codes in their content | |
129 | (i.e., after the part that matches C<m/\A=[a-zA-Z]\S*\s*/>), as in: | |
130 | ||
131 | =head1 Did You Remember to C<use strict;>? | |
132 | ||
133 | In other words, the Pod processing handler for "head1" will apply the | |
134 | same processing to "Did You Remember to CE<lt>use strict;>?" that it | |
135 | would to an ordinary paragraph -- i.e., formatting codes (like | |
136 | "CE<lt>...>") are parsed and presumably formatted appropriately, and | |
137 | whitespace in the form of literal spaces and/or tabs is not | |
138 | significant. | |
139 | ||
140 | =item * | |
141 | ||
142 | A B<verbatim paragraph>. The first line of this paragraph must be a | |
143 | literal space or tab, and this paragraph must not be inside a "=begin | |
144 | I<identifier>", ... "=end I<identifier>" sequence unless | |
145 | "I<identifier>" begins with a colon (":"). That is, if a paragraph | |
146 | starts with a literal space or tab, but I<is> inside a | |
147 | "=begin I<identifier>", ... "=end I<identifier>" region, then it's | |
148 | a data paragraph, unless "I<identifier>" begins with a colon. | |
149 | ||
150 | Whitespace I<is> significant in verbatim paragraphs (although, in | |
151 | processing, tabs are probably expanded). | |
152 | ||
153 | =item * | |
154 | ||
155 | An B<ordinary paragraph>. A paragraph is an ordinary paragraph | |
156 | if its first line matches neither C<m/\A=[a-zA-Z]/> nor | |
157 | C<m/\A[ \t]/>, I<and> if it's not inside a "=begin I<identifier>", | |
158 | ... "=end I<identifier>" sequence unless "I<identifier>" begins with | |
159 | a colon (":"). | |
160 | ||
161 | =item * | |
162 | ||
163 | A B<data paragraph>. This is a paragraph that I<is> inside a "=begin | |
164 | I<identifier>" ... "=end I<identifier>" sequence where | |
165 | "I<identifier>" does I<not> begin with a literal colon (":"). In | |
166 | some sense, a data paragraph is not part of Pod at all (i.e., | |
167 | effectively it's "out-of-band"), since it's not subject to most kinds | |
168 | of Pod parsing; but it is specified here, since Pod | |
169 | parsers need to be able to call an event for it, or store it in some | |
170 | form in a parse tree, or at least just parse I<around> it. | |
171 | ||
172 | =back | |
173 | ||
174 | For example: consider the following paragraphs: | |
175 | ||
176 | # <- that's the 0th column | |
177 | ||
178 | =head1 Foo | |
210b36aa | 179 | |
8a93676d | 180 | Stuff |
210b36aa | 181 | |
8a93676d | 182 | $foo->bar |
210b36aa | 183 | |
8a93676d SB |
184 | =cut |
185 | ||
186 | Here, "=head1 Foo" and "=cut" are command paragraphs because the first | |
187 | line of each matches C<m/\A=[a-zA-Z]/>. "I<[space][space]>$foo->bar" | |
188 | is a verbatim paragraph, because its first line starts with a literal | |
189 | whitespace character (and there's no "=begin"..."=end" region around). | |
190 | ||
191 | The "=begin I<identifier>" ... "=end I<identifier>" commands stop | |
192 | paragraphs that they surround from being parsed as data or verbatim | |
193 | paragraphs, if I<identifier> doesn't begin with a colon. This | |
194 | is discussed in detail in the section | |
195 | L</About Data Paragraphs and "=beginE<sol>=end" Regions>. | |
196 | ||
197 | =head1 Pod Commands | |
198 | ||
199 | This section is intended to supplement and clarify the discussion in | |
200 | L<perlpod/"Command Paragraph">. These are the currently recognized | |
201 | Pod commands: | |
202 | ||
203 | =over | |
204 | ||
205 | =item "=head1", "=head2", "=head3", "=head4" | |
206 | ||
207 | This command indicates that the text in the remainder of the paragraph | |
208 | is a heading. That text may contain formatting codes. Examples: | |
209 | ||
210 | =head1 Object Attributes | |
210b36aa | 211 | |
8a93676d SB |
212 | =head3 What B<Not> to Do! |
213 | ||
214 | =item "=pod" | |
215 | ||
216 | This command indicates that this paragraph begins a Pod block. (If we | |
217 | are already in the middle of a Pod block, this command has no effect at | |
218 | all.) If there is any text in this command paragraph after "=pod", | |
219 | it must be ignored. Examples: | |
220 | ||
221 | =pod | |
210b36aa | 222 | |
8a93676d | 223 | This is a plain Pod paragraph. |
210b36aa | 224 | |
8a93676d SB |
225 | =pod This text is ignored. |
226 | ||
227 | =item "=cut" | |
228 | ||
229 | This command indicates that this line is the end of this previously | |
230 | started Pod block. If there is any text after "=cut" on the line, it must be | |
231 | ignored. Examples: | |
232 | ||
233 | =cut | |
234 | ||
235 | =cut The documentation ends here. | |
236 | ||
237 | =cut | |
238 | # This is the first line of program text. | |
239 | sub foo { # This is the second. | |
240 | ||
241 | It is an error to try to I<start> a Pod black with a "=cut" command. In | |
242 | that case, the Pod processor must halt parsing of the input file, and | |
243 | must by default emit a warning. | |
244 | ||
245 | =item "=over" | |
246 | ||
247 | This command indicates that this is the start of a list/indent | |
248 | region. If there is any text following the "=over", it must consist | |
249 | of only a nonzero positive numeral. The semantics of this numeral is | |
250 | explained in the L</"About =over...=back Regions"> section, further | |
251 | below. Formatting codes are not expanded. Examples: | |
252 | ||
253 | =over 3 | |
210b36aa | 254 | |
8a93676d | 255 | =over 3.5 |
210b36aa | 256 | |
8a93676d SB |
257 | =over |
258 | ||
259 | =item "=item" | |
260 | ||
261 | This command indicates that an item in a list begins here. Formatting | |
262 | codes are processed. The semantics of the (optional) text in the | |
263 | remainder of this paragraph are | |
264 | explained in the L</"About =over...=back Regions"> section, further | |
265 | below. Examples: | |
266 | ||
267 | =item | |
210b36aa | 268 | |
8a93676d | 269 | =item * |
210b36aa | 270 | |
8a93676d | 271 | =item * |
210b36aa | 272 | |
8a93676d | 273 | =item 14 |
210b36aa | 274 | |
8a93676d | 275 | =item 3. |
210b36aa | 276 | |
8a93676d | 277 | =item C<< $thing->stuff(I<dodad>) >> |
210b36aa | 278 | |
8a93676d SB |
279 | =item For transporting us beyond seas to be tried for pretended |
280 | offenses | |
210b36aa | 281 | |
8a93676d SB |
282 | =item He is at this time transporting large armies of foreign |
283 | mercenaries to complete the works of death, desolation and | |
284 | tyranny, already begun with circumstances of cruelty and perfidy | |
285 | scarcely paralleled in the most barbarous ages, and totally | |
286 | unworthy the head of a civilized nation. | |
287 | ||
288 | =item "=back" | |
289 | ||
290 | This command indicates that this is the end of the region begun | |
291 | by the most recent "=over" command. It permits no text after the | |
292 | "=back" command. | |
293 | ||
294 | =item "=begin formatname" | |
295 | ||
296 | This marks the following paragraphs (until the matching "=end | |
297 | formatname") as being for some special kind of processing. Unless | |
298 | "formatname" begins with a colon, the contained non-command | |
299 | paragraphs are data paragraphs. But if "formatname" I<does> begin | |
300 | with a colon, then non-command paragraphs are ordinary paragraphs | |
301 | or data paragraphs. This is discussed in detail in the section | |
302 | L</About Data Paragraphs and "=beginE<sol>=end" Regions>. | |
303 | ||
304 | It is advised that formatnames match the regexp | |
305 | C<m/\A:?[-a-zA-Z0-9_]+\z/>. Implementors should anticipate future | |
306 | expansion in the semantics and syntax of the first parameter | |
307 | to "=begin"/"=end"/"=for". | |
308 | ||
309 | =item "=end formatname" | |
310 | ||
311 | This marks the end of the region opened by the matching | |
312 | "=begin formatname" region. If "formatname" is not the formatname | |
313 | of the most recent open "=begin formatname" region, then this | |
314 | is an error, and must generate an error message. This | |
315 | is discussed in detail in the section | |
316 | L</About Data Paragraphs and "=beginE<sol>=end" Regions>. | |
317 | ||
318 | =item "=for formatname text..." | |
319 | ||
320 | This is synonymous with: | |
321 | ||
322 | =begin formatname | |
210b36aa | 323 | |
8a93676d | 324 | text... |
210b36aa | 325 | |
8a93676d SB |
326 | =end formatname |
327 | ||
328 | That is, it creates a region consisting of a single paragraph; that | |
329 | paragraph is to be treated as a normal paragraph if "formatname" | |
330 | begins with a ":"; if "formatname" I<doesn't> begin with a colon, | |
331 | then "text..." will constitute a data paragraph. There is no way | |
332 | to use "=for formatname text..." to express "text..." as a verbatim | |
333 | paragraph. | |
334 | ||
335 | =back | |
336 | ||
337 | If a Pod processor sees any command other than the ones listed | |
338 | above (like "=head", or "=haed1", or "=stuff", or "=cuttlefish", | |
339 | or "=w123"), that processor must by default treat this as an | |
340 | error. It must not process the paragraph beginning with that | |
341 | command, must by default warn of this as an error, and may | |
342 | abort the parse. A Pod parser may allow a way for particular | |
343 | applications to add to the above list of known commands, and to | |
344 | stipulate, for each additional command, whether formatting | |
345 | codes should be processed. | |
346 | ||
347 | Future versions of this specification may add additional | |
348 | commands. | |
349 | ||
350 | ||
351 | ||
352 | =head1 Pod Formatting Codes | |
353 | ||
354 | (Note that in previous drafts of this document and of perlpod, | |
355 | formatting codes were referred to as "interior sequences", and | |
356 | this term may still be found in the documentation for Pod parsers, | |
357 | and in error messages from Pod processors.) | |
358 | ||
359 | There are two syntaxes for formatting codes: | |
360 | ||
361 | =over | |
362 | ||
363 | =item * | |
364 | ||
365 | A formatting code starts with a capital letter (just US-ASCII [A-Z]) | |
366 | followed by a "<", any number of characters, and ending with the first | |
367 | matching ">". Examples: | |
368 | ||
369 | That's what I<you> think! | |
370 | ||
371 | What's C<dump()> for? | |
372 | ||
373 | X<C<chmod> and C<unlink()> Under Different Operating Systems> | |
374 | ||
375 | =item * | |
376 | ||
377 | A formatting code starts with a capital letter (just US-ASCII [A-Z]) | |
378 | followed by two or more "<"'s, one or more whitespace characters, | |
379 | any number of characters, one or more whitespace characters, | |
380 | and ending with the first matching sequence of two or more ">"'s, where | |
381 | the number of ">"'s equals the number of "<"'s in the opening of this | |
382 | formatting code. Examples: | |
383 | ||
384 | That's what I<< you >> think! | |
385 | ||
386 | C<<< open(X, ">>thing.dat") || die $! >>> | |
387 | ||
388 | B<< $foo->bar(); >> | |
389 | ||
390 | With this syntax, the whitespace character(s) after the "CE<lt><<" | |
391 | and before the ">>" (or whatever letter) are I<not> renderable -- they | |
392 | do not signify whitespace, are merely part of the formatting codes | |
393 | themselves. That is, these are all synonymous: | |
394 | ||
395 | C<thing> | |
396 | C<< thing >> | |
397 | C<< thing >> | |
398 | C<<< thing >>> | |
399 | C<<<< | |
400 | thing | |
401 | >>>> | |
402 | ||
403 | and so on. | |
404 | ||
405 | =back | |
406 | ||
407 | In parsing Pod, a notably tricky part is the correct parsing of | |
408 | (potentially nested!) formatting codes. Implementors should | |
409 | consult the code in the C<parse_text> routine in Pod::Parser as an | |
410 | example of a correct implementation. | |
411 | ||
412 | =over | |
413 | ||
414 | =item C<IE<lt>textE<gt>> -- italic text | |
415 | ||
416 | See the brief discussion in L<perlpod/"Formatting Codes">. | |
417 | ||
418 | =item C<BE<lt>textE<gt>> -- bold text | |
419 | ||
420 | See the brief discussion in L<perlpod/"Formatting Codes">. | |
421 | ||
422 | =item C<CE<lt>codeE<gt>> -- code text | |
423 | ||
424 | See the brief discussion in L<perlpod/"Formatting Codes">. | |
425 | ||
426 | =item C<FE<lt>filenameE<gt>> -- style for filenames | |
427 | ||
428 | See the brief discussion in L<perlpod/"Formatting Codes">. | |
429 | ||
430 | =item C<XE<lt>topic nameE<gt>> -- an index entry | |
431 | ||
432 | See the brief discussion in L<perlpod/"Formatting Codes">. | |
433 | ||
434 | This code is unusual in that most formatters completely discard | |
435 | this code and its content. Other formatters will render it with | |
436 | invisible codes that can be used in building an index of | |
437 | the current document. | |
438 | ||
439 | =item C<ZE<lt>E<gt>> -- a null (zero-effect) formatting code | |
440 | ||
441 | Discussed briefly in L<perlpod/"Formatting Codes">. | |
442 | ||
443 | This code is unusual is that it should have no content. That is, | |
444 | a processor may complain if it sees C<ZE<lt>potatoesE<gt>>. Whether | |
445 | or not it complains, the I<potatoes> text should ignored. | |
446 | ||
447 | =item C<LE<lt>nameE<gt>> -- a hyperlink | |
448 | ||
449 | The complicated syntaxes of this code are discussed at length in | |
450 | L<perlpod/"Formatting Codes">, and implementation details are | |
451 | discussed below, in L</"About LE<lt>...E<gt> Codes">. Parsing the | |
452 | contents of LE<lt>content> is tricky. Notably, the content has to be | |
453 | checked for whether it looks like a URL, or whether it has to be split | |
454 | on literal "|" and/or "/" (in the right order!), and so on, | |
455 | I<before> EE<lt>...> codes are resolved. | |
456 | ||
457 | =item C<EE<lt>escapeE<gt>> -- a character escape | |
458 | ||
459 | See L<perlpod/"Formatting Codes">, and several points in | |
460 | L</Notes on Implementing Pod Processors>. | |
461 | ||
462 | =item C<SE<lt>textE<gt>> -- text contains non-breaking spaces | |
463 | ||
464 | This formatting code is syntactically simple, but semantically | |
465 | complex. What it means is that each space in the printable | |
466 | content of this code signifies a nonbreaking space. | |
467 | ||
468 | Consider: | |
469 | ||
470 | C<$x ? $y : $z> | |
471 | ||
472 | S<C<$x ? $y : $z>> | |
473 | ||
474 | Both signify the monospace (c[ode] style) text consisting of | |
475 | "$x", one space, "?", one space, ":", one space, "$z". The | |
476 | difference is that in the latter, with the S code, those spaces | |
477 | are not "normal" spaces, but instead are nonbreaking spaces. | |
478 | ||
479 | =back | |
480 | ||
481 | ||
482 | If a Pod processor sees any formatting code other than the ones | |
483 | listed above (as in "NE<lt>...>", or "QE<lt>...>", etc.), that | |
484 | processor must by default treat this as an error. | |
485 | A Pod parser may allow a way for particular | |
486 | applications to add to the above list of known formatting codes; | |
487 | a Pod parser might even allow a way to stipulate, for each additional | |
488 | command, whether it requires some form of special processing, as | |
489 | LE<lt>...> does. | |
490 | ||
491 | Future versions of this specification may add additional | |
492 | formatting codes. | |
493 | ||
494 | Historical note: A few older Pod processors would not see a ">" as | |
495 | closing a "CE<lt>" code, if the ">" was immediately preceded by | |
496 | a "-". This was so that this: | |
497 | ||
498 | C<$foo->bar> | |
499 | ||
500 | would parse as equivalent to this: | |
501 | ||
502 | C<$foo-E<lt>bar> | |
503 | ||
504 | instead of as equivalent to a "C" formatting code containing | |
505 | only "$foo-", and then a "bar>" outside the "C" formatting code. This | |
506 | problem has since been solved by the addition of syntaxes like this: | |
507 | ||
508 | C<< $foo->bar >> | |
509 | ||
510 | Compliant parsers must not treat "->" as special. | |
511 | ||
512 | Formatting codes absolutely cannot span paragraphs. If a code is | |
513 | opened in one paragraph, and no closing code is found by the end of | |
514 | that paragraph, the Pod parser must close that formatting code, | |
515 | and should complain (as in "Unterminated I code in the paragraph | |
516 | starting at line 123: 'Time objects are not...'"). So these | |
517 | two paragraphs: | |
518 | ||
519 | I<I told you not to do this! | |
210b36aa | 520 | |
8a93676d SB |
521 | Don't make me say it again!> |
522 | ||
523 | ...must I<not> be parsed as two paragraphs in italics (with the I | |
524 | code starting in one paragraph and starting in another.) Instead, | |
525 | the first paragraph should generate a warning, but that aside, the | |
526 | above code must parse as if it were: | |
527 | ||
528 | I<I told you not to do this!> | |
210b36aa | 529 | |
8a93676d SB |
530 | Don't make me say it again!E<gt> |
531 | ||
532 | (In SGMLish jargon, all Pod commands are like block-level | |
533 | elements, whereas all Pod formatting codes are like inline-level | |
534 | elements.) | |
535 | ||
536 | ||
537 | ||
538 | =head1 Notes on Implementing Pod Processors | |
539 | ||
540 | The following is a long section of miscellaneous requirements | |
541 | and suggestions to do with Pod processing. | |
542 | ||
543 | =over | |
544 | ||
545 | =item * | |
546 | ||
547 | Pod formatters should tolerate lines in verbatim blocks that are of | |
548 | any length, even if that means having to break them (possibly several | |
549 | times, for very long lines) to avoid text running off the side of the | |
550 | page. Pod formatters may warn of such line-breaking. Such warnings | |
551 | are particularly appropriate for lines are over 100 characters long, which | |
552 | are usually not intentional. | |
553 | ||
554 | =item * | |
555 | ||
556 | Pod parsers must recognize I<all> of the three well-known newline | |
557 | formats: CR, LF, and CRLF. See L<perlport|perlport>. | |
558 | ||
559 | =item * | |
560 | ||
561 | Pod parsers should accept input lines that are of any length. | |
562 | ||
563 | =item * | |
564 | ||
565 | Since Perl recognizes a Unicode Byte Order Mark at the start of files | |
566 | as signaling that the file is Unicode encoded as in UTF-16 (whether | |
567 | big-endian or little-endian) or UTF-8, Pod parsers should do the | |
568 | same. Otherwise, the character encoding should be understood as | |
569 | being UTF-8 if the first highbit byte sequence in the file seems | |
570 | valid as a UTF-8 sequence, or otherwise as Latin-1. | |
571 | ||
572 | Future versions of this specification may specify | |
573 | how Pod can accept other encodings. Presumably treatment of other | |
574 | encodings in Pod parsing would be as in XML parsing: whatever the | |
575 | encoding declared by a particular Pod file, content is to be | |
576 | stored in memory as Unicode characters. | |
577 | ||
578 | =item * | |
579 | ||
580 | The well known Unicode Byte Order Marks are as follows: if the | |
581 | file begins with the two literal byte values 0xFE 0xFF, this is | |
582 | the BOM for big-endian UTF-16. If the file begins with the two | |
583 | literal byte value 0xFF 0xFE, this is the BOM for little-endian | |
584 | UTF-16. If the file begins with the three literal byte values | |
585 | 0xEF 0xBB 0xBF, this is the BOM for UTF-8. | |
586 | ||
587 | =for comment | |
588 | use bytes; print map sprintf(" 0x%02X", ord $_), split '', "\x{feff}"; | |
589 | 0xEF 0xBB 0xBF | |
590 | ||
591 | =for comment | |
592 | If toke.c is modified to support UTF32, add mention of those here. | |
593 | ||
594 | =item * | |
595 | ||
596 | A naive but sufficient heuristic for testing the first highbit | |
597 | byte-sequence in a BOM-less file (whether in code or in Pod!), to see | |
598 | whether that sequence is valid as UTF-8 (RFC 2279) is to check whether | |
599 | that the first byte in the sequence is in the range 0xC0 - 0xFD | |
600 | I<and> whether the next byte is in the range | |
601 | 0x80 - 0xBF. If so, the parser may conclude that this file is in | |
602 | UTF-8, and all highbit sequences in the file should be assumed to | |
603 | be UTF-8. Otherwise the parser should treat the file as being | |
604 | in Latin-1. In the unlikely circumstance that the first highbit | |
605 | sequence in a truly non-UTF-8 file happens to appear to be UTF-8, one | |
606 | can cater to our heuristic (as well as any more intelligent heuristic) | |
607 | by prefacing that line with a comment line containing a highbit | |
608 | sequence that is clearly I<not> valid as UTF-8. A line consisting | |
609 | of simply "#", an e-acute, and any non-highbit byte, | |
610 | is sufficient to establish this file's encoding. | |
611 | ||
612 | =for comment | |
613 | If/WHEN some brave soul makes these heuristics into a generic | |
fae2c0fb | 614 | text-file class (or PerlIO layer?), we can presumably delete |
8a93676d | 615 | mention of these icky details from this file, and can instead |
fae2c0fb | 616 | tell people to just use appropriate class/layer. |
8a93676d | 617 | Auto-recognition of newline sequences would be another desirable |
fae2c0fb | 618 | feature of such a class/layer. |
8a93676d SB |
619 | HINT HINT HINT. |
620 | ||
621 | =for comment | |
622 | "The probability that a string of characters | |
623 | in any other encoding appears as valid UTF-8 is low" - RFC2279 | |
624 | ||
625 | =item * | |
626 | ||
627 | This document's requirements and suggestions about encodings | |
628 | do not apply to Pod processors running on non-ASCII platforms, | |
629 | notably EBCDIC platforms. | |
630 | ||
631 | =item * | |
632 | ||
633 | Pod processors must treat a "=for [label] [content...]" paragraph as | |
634 | meaning the same thing as a "=begin [label]" paragraph, content, and | |
635 | an "=end [label]" paragraph. (The parser may conflate these two | |
636 | constructs, or may leave them distinct, in the expectation that the | |
637 | formatter will nevertheless treat them the same.) | |
638 | ||
639 | =item * | |
640 | ||
641 | When rendering Pod to a format that allows comments (i.e., to nearly | |
642 | any format other than plaintext), a Pod formatter must insert comment | |
643 | text identifying its name and version number, and the name and | |
644 | version numbers of any modules it might be using to process the Pod. | |
645 | Minimal examples: | |
646 | ||
647 | %% POD::Pod2PS v3.14159, using POD::Parser v1.92 | |
210b36aa | 648 | |
8a93676d | 649 | <!-- Pod::HTML v3.14159, using POD::Parser v1.92 --> |
210b36aa | 650 | |
8a93676d | 651 | {\doccomm generated by Pod::Tree::RTF 3.14159 using Pod::Tree 1.08} |
210b36aa | 652 | |
8a93676d SB |
653 | .\" Pod::Man version 3.14159, using POD::Parser version 1.92 |
654 | ||
655 | Formatters may also insert additional comments, including: the | |
656 | release date of the Pod formatter program, the contact address for | |
657 | the author(s) of the formatter, the current time, the name of input | |
658 | file, the formatting options in effect, version of Perl used, etc. | |
659 | ||
660 | Formatters may also choose to note errors/warnings as comments, | |
661 | besides or instead of emitting them otherwise (as in messages to | |
662 | STDERR, or C<die>ing). | |
663 | ||
664 | =item * | |
665 | ||
666 | Pod parsers I<may> emit warnings or error messages ("Unknown E code | |
667 | EE<lt>zslig>!") to STDERR (whether through printing to STDERR, or | |
668 | C<warn>ing/C<carp>ing, or C<die>ing/C<croak>ing), but I<must> allow | |
669 | suppressing all such STDERR output, and instead allow an option for | |
670 | reporting errors/warnings | |
671 | in some other way, whether by triggering a callback, or noting errors | |
672 | in some attribute of the document object, or some similarly unobtrusive | |
673 | mechanism -- or even by appending a "Pod Errors" section to the end of | |
674 | the parsed form of the document. | |
675 | ||
676 | =item * | |
677 | ||
678 | In cases of exceptionally aberrant documents, Pod parsers may abort the | |
679 | parse. Even then, using C<die>ing/C<croak>ing is to be avoided; where | |
680 | possible, the parser library may simply close the input file | |
681 | and add text like "*** Formatting Aborted ***" to the end of the | |
682 | (partial) in-memory document. | |
683 | ||
684 | =item * | |
685 | ||
686 | In paragraphs where formatting codes (like EE<lt>...>, BE<lt>...>) | |
687 | are understood (i.e., I<not> verbatim paragraphs, but I<including> | |
688 | ordinary paragraphs, and command paragraphs that produce renderable | |
689 | text, like "=head1"), literal whitespace should generally be considered | |
690 | "insignificant", in that one literal space has the same meaning as any | |
691 | (nonzero) number of literal spaces, literal newlines, and literal tabs | |
692 | (as long as this produces no blank lines, since those would terminate | |
693 | the paragraph). Pod parsers should compact literal whitespace in each | |
694 | processed paragraph, but may provide an option for overriding this | |
695 | (since some processing tasks do not require it), or may follow | |
696 | additional special rules (for example, specially treating | |
697 | period-space-space or period-newline sequences). | |
698 | ||
699 | =item * | |
700 | ||
701 | Pod parsers should not, by default, try to coerce apostrophe (') and | |
702 | quote (") into smart quotes (little 9's, 66's, 99's, etc), nor try to | |
703 | turn backtick (`) into anything else but a single backtick character | |
704 | (distinct from an openquote character!), nor "--" into anything but | |
705 | two minus signs. They I<must never> do any of those things to text | |
706 | in CE<lt>...> formatting codes, and never I<ever> to text in verbatim | |
707 | paragraphs. | |
708 | ||
709 | =item * | |
710 | ||
711 | When rendering Pod to a format that has two kinds of hyphens (-), one | |
712 | that's a nonbreaking hyphen, and another that's a breakable hyphen | |
713 | (as in "object-oriented", which can be split across lines as | |
714 | "object-", newline, "oriented"), formatters are encouraged to | |
715 | generally translate "-" to nonbreaking hyphen, but may apply | |
716 | heuristics to convert some of these to breaking hyphens. | |
717 | ||
718 | =item * | |
719 | ||
720 | Pod formatters should make reasonable efforts to keep words of Perl | |
721 | code from being broken across lines. For example, "Foo::Bar" in some | |
722 | formatting systems is seen as eligible for being broken across lines | |
723 | as "Foo::" newline "Bar" or even "Foo::-" newline "Bar". This should | |
724 | be avoided where possible, either by disabling all line-breaking in | |
725 | mid-word, or by wrapping particular words with internal punctuation | |
726 | in "don't break this across lines" codes (which in some formats may | |
727 | not be a single code, but might be a matter of inserting non-breaking | |
728 | zero-width spaces between every pair of characters in a word.) | |
729 | ||
730 | =item * | |
731 | ||
732 | Pod parsers should, by default, expand tabs in verbatim paragraphs as | |
733 | they are processed, before passing them to the formatter or other | |
734 | processor. Parsers may also allow an option for overriding this. | |
735 | ||
736 | =item * | |
737 | ||
738 | Pod parsers should, by default, remove newlines from the end of | |
739 | ordinary and verbatim paragraphs before passing them to the | |
740 | formatter. For example, while the paragraph you're reading now | |
741 | could be considered, in Pod source, to end with (and contain) | |
742 | the newline(s) that end it, it should be processed as ending with | |
743 | (and containing) the period character that ends this sentence. | |
744 | ||
745 | =item * | |
746 | ||
747 | Pod parsers, when reporting errors, should make some effort to report | |
748 | an approximate line number ("Nested EE<lt>>'s in Paragraph #52, near | |
749 | line 633 of Thing/Foo.pm!"), instead of merely noting the paragraph | |
750 | number ("Nested EE<lt>>'s in Paragraph #52 of Thing/Foo.pm!"). Where | |
751 | this is problematic, the paragraph number should at least be | |
752 | accompanied by an excerpt from the paragraph ("Nested EE<lt>>'s in | |
753 | Paragraph #52 of Thing/Foo.pm, which begins 'Read/write accessor for | |
754 | the CE<lt>interest rate> attribute...'"). | |
755 | ||
756 | =item * | |
757 | ||
758 | Pod parsers, when processing a series of verbatim paragraphs one | |
759 | after another, should consider them to be one large verbatim | |
760 | paragraph that happens to contain blank lines. I.e., these two | |
d1be9408 | 761 | lines, which have a blank line between them: |
8a93676d SB |
762 | |
763 | use Foo; | |
764 | ||
765 | print Foo->VERSION | |
766 | ||
767 | should be unified into one paragraph ("\tuse Foo;\n\n\tprint | |
768 | Foo->VERSION") before being passed to the formatter or other | |
769 | processor. Parsers may also allow an option for overriding this. | |
770 | ||
771 | While this might be too cumbersome to implement in event-based Pod | |
772 | parsers, it is straightforward for parsers that return parse trees. | |
773 | ||
774 | =item * | |
775 | ||
776 | Pod formatters, where feasible, are advised to avoid splitting short | |
777 | verbatim paragraphs (under twelve lines, say) across pages. | |
778 | ||
779 | =item * | |
780 | ||
781 | Pod parsers must treat a line with only spaces and/or tabs on it as a | |
782 | "blank line" such as separates paragraphs. (Some older parsers | |
783 | recognized only two adjacent newlines as a "blank line" but would not | |
784 | recognize a newline, a space, and a newline, as a blank line. This | |
785 | is noncompliant behavior.) | |
786 | ||
787 | =item * | |
788 | ||
789 | Authors of Pod formatters/processors should make every effort to | |
790 | avoid writing their own Pod parser. There are already several in | |
791 | CPAN, with a wide range of interface styles -- and one of them, | |
792 | Pod::Parser, comes with modern versions of Perl. | |
793 | ||
794 | =item * | |
795 | ||
796 | Characters in Pod documents may be conveyed either as literals, or by | |
797 | number in EE<lt>n> codes, or by an equivalent mnemonic, as in | |
798 | EE<lt>eacute> which is exactly equivalent to EE<lt>233>. | |
799 | ||
800 | Characters in the range 32-126 refer to those well known US-ASCII | |
801 | characters (also defined there by Unicode, with the same meaning), | |
802 | which all Pod formatters must render faithfully. Characters | |
803 | in the ranges 0-31 and 127-159 should not be used (neither as | |
804 | literals, nor as EE<lt>number> codes), except for the | |
210b36aa | 805 | literal byte-sequences for newline (13, 13 10, or 10), and tab (9). |
8a93676d SB |
806 | |
807 | Characters in the range 160-255 refer to Latin-1 characters (also | |
808 | defined there by Unicode, with the same meaning). Characters above | |
809 | 255 should be understood to refer to Unicode characters. | |
810 | ||
811 | =item * | |
812 | ||
813 | Be warned | |
814 | that some formatters cannot reliably render characters outside 32-126; | |
815 | and many are able to handle 32-126 and 160-255, but nothing above | |
816 | 255. | |
817 | ||
818 | =item * | |
819 | ||
820 | Besides the well-known "EE<lt>lt>" and "EE<lt>gt>" codes for | |
821 | less-than and greater-than, Pod parsers must understand "EE<lt>sol>" | |
822 | for "/" (solidus, slash), and "EE<lt>verbar>" for "|" (vertical bar, | |
823 | pipe). Pod parsers should also understand "EE<lt>lchevron>" and | |
824 | "EE<lt>rchevron>" as legacy codes for characters 171 and 187, i.e., | |
825 | "left-pointing double angle quotation mark" = "left pointing | |
826 | guillemet" and "right-pointing double angle quotation mark" = "right | |
827 | pointing guillemet". (These look like little "<<" and ">>", and they | |
828 | are now preferably expressed with the HTML/XHTML codes "EE<lt>laquo>" | |
829 | and "EE<lt>raquo>".) | |
830 | ||
831 | =item * | |
832 | ||
833 | Pod parsers should understand all "EE<lt>html>" codes as defined | |
834 | in the entity declarations in the most recent XHTML specification at | |
835 | C<www.W3.org>. Pod parsers must understand at least the entities | |
836 | that define characters in the range 160-255 (Latin-1). Pod parsers, | |
837 | when faced with some unknown "EE<lt>I<identifier>>" code, | |
838 | shouldn't simply replace it with nullstring (by default, at least), | |
839 | but may pass it through as a string consisting of the literal characters | |
840 | E, less-than, I<identifier>, greater-than. Or Pod parsers may offer the | |
841 | alternative option of processing such unknown | |
842 | "EE<lt>I<identifier>>" codes by firing an event especially | |
843 | for such codes, or by adding a special node-type to the in-memory | |
844 | document tree. Such "EE<lt>I<identifier>>" may have special meaning | |
845 | to some processors, or some processors may choose to add them to | |
846 | a special error report. | |
847 | ||
848 | =item * | |
849 | ||
850 | Pod parsers must also support the XHTML codes "EE<lt>quot>" for | |
851 | character 34 (doublequote, "), "EE<lt>amp>" for character 38 | |
852 | (ampersand, &), and "EE<lt>apos>" for character 39 (apostrophe, '). | |
853 | ||
854 | =item * | |
855 | ||
856 | Note that in all cases of "EE<lt>whatever>", I<whatever> (whether | |
857 | an htmlname, or a number in any base) must consist only of | |
858 | alphanumeric characters -- that is, I<whatever> must watch | |
859 | C<m/\A\w+\z/>. So "EE<lt> 0 1 2 3 >" is invalid, because | |
860 | it contains spaces, which aren't alphanumeric characters. This | |
861 | presumably does not I<need> special treatment by a Pod processor; | |
862 | " 0 1 2 3 " doesn't look like a number in any base, so it would | |
863 | presumably be looked up in the table of HTML-like names. Since | |
210b36aa | 864 | there isn't (and cannot be) an HTML-like entity called " 0 1 2 3 ", |
8a93676d SB |
865 | this will be treated as an error. However, Pod processors may |
866 | treat "EE<lt> 0 1 2 3 >" or "EE<lt>e-acute>" as I<syntactically> | |
867 | invalid, potentially earning a different error message than the | |
868 | error message (or warning, or event) generated by a merely unknown | |
869 | (but theoretically valid) htmlname, as in "EE<lt>qacute>" | |
870 | [sic]. However, Pod parsers are not required to make this | |
871 | distinction. | |
872 | ||
873 | =item * | |
874 | ||
875 | Note that EE<lt>number> I<must not> be interpreted as simply | |
876 | "codepoint I<number> in the current/native character set". It always | |
877 | means only "the character represented by codepoint I<number> in | |
878 | Unicode." (This is identical to the semantics of &#I<number>; in XML.) | |
879 | ||
880 | This will likely require many formatters to have tables mapping from | |
881 | treatable Unicode codepoints (such as the "\xE9" for the e-acute | |
882 | character) to the escape sequences or codes necessary for conveying | |
883 | such sequences in the target output format. A converter to *roff | |
884 | would, for example know that "\xE9" (whether conveyed literally, or via | |
885 | a EE<lt>...> sequence) is to be conveyed as "e\\*'". | |
8939ba94 | 886 | Similarly, a program rendering Pod in a Mac OS application window, would |
8a93676d | 887 | presumably need to know that "\xE9" maps to codepoint 142 in MacRoman |
8939ba94 | 888 | encoding that (at time of writing) is native for Mac OS. Such |
8a93676d SB |
889 | Unicode2whatever mappings are presumably already widely available for |
890 | common output formats. (Such mappings may be incomplete! Implementers | |
891 | are not expected to bend over backwards in an attempt to render | |
892 | Cherokee syllabics, Etruscan runes, Byzantine musical symbols, or any | |
893 | of the other weird things that Unicode can encode.) And | |
894 | if a Pod document uses a character not found in such a mapping, the | |
895 | formatter should consider it an unrenderable character. | |
896 | ||
897 | =item * | |
898 | ||
899 | If, surprisingly, the implementor of a Pod formatter can't find a | |
900 | satisfactory pre-existing table mapping from Unicode characters to | |
901 | escapes in the target format (e.g., a decent table of Unicode | |
902 | characters to *roff escapes), it will be necessary to build such a | |
903 | table. If you are in this circumstance, you should begin with the | |
904 | characters in the range 0x00A0 - 0x00FF, which is mostly the heavily | |
905 | used accented characters. Then proceed (as patience permits and | |
906 | fastidiousness compels) through the characters that the (X)HTML | |
907 | standards groups judged important enough to merit mnemonics | |
908 | for. These are declared in the (X)HTML specifications at the | |
909 | www.W3.org site. At time of writing (September 2001), the most recent | |
910 | entity declaration files are: | |
911 | ||
912 | http://www.w3.org/TR/xhtml1/DTD/xhtml-lat1.ent | |
913 | http://www.w3.org/TR/xhtml1/DTD/xhtml-special.ent | |
914 | http://www.w3.org/TR/xhtml1/DTD/xhtml-symbol.ent | |
915 | ||
916 | Then you can progress through any remaining notable Unicode characters | |
917 | in the range 0x2000-0x204D (consult the character tables at | |
918 | www.unicode.org), and whatever else strikes your fancy. For example, | |
919 | in F<xhtml-symbol.ent>, there is the entry: | |
920 | ||
921 | <!ENTITY infin "∞"> <!-- infinity, U+221E ISOtech --> | |
922 | ||
923 | While the mapping "infin" to the character "\x{221E}" will (hopefully) | |
924 | have been already handled by the Pod parser, the presence of the | |
925 | character in this file means that it's reasonably important enough to | |
926 | include in a formatter's table that maps from notable Unicode characters | |
927 | to the codes necessary for rendering them. So for a Unicode-to-*roff | |
928 | mapping, for example, this would merit the entry: | |
929 | ||
930 | "\x{221E}" => '\(in', | |
931 | ||
932 | It is eagerly hoped that in the future, increasing numbers of formats | |
933 | (and formatters) will support Unicode characters directly (as (X)HTML | |
934 | does with C<∞>, C<∞>, or C<∞>), reducing the need | |
935 | for idiosyncratic mappings of Unicode-to-I<my_escapes>. | |
936 | ||
937 | =item * | |
938 | ||
939 | It is up to individual Pod formatter to display good judgment when | |
940 | confronted with an unrenderable character (which is distinct from an | |
941 | unknown EE<lt>thing> sequence that the parser couldn't resolve to | |
942 | anything, renderable or not). It is good practice to map Latin letters | |
943 | with diacritics (like "EE<lt>eacute>"/"EE<lt>233>") to the corresponding | |
944 | unaccented US-ASCII letters (like a simple character 101, "e"), but | |
210b36aa | 945 | clearly this is often not feasible, and an unrenderable character may |
8a93676d SB |
946 | be represented as "?", or the like. In attempting a sane fallback |
947 | (as from EE<lt>233> to "e"), Pod formatters may use the | |
948 | %Latin1Code_to_fallback table in L<Pod::Escapes|Pod::Escapes>, or | |
949 | L<Text::Unidecode|Text::Unidecode>, if available. | |
950 | ||
951 | For example, this Pod text: | |
952 | ||
953 | magic is enabled if you set C<$Currency> to 'E<euro>'. | |
954 | ||
955 | may be rendered as: | |
956 | "magic is enabled if you set C<$Currency> to 'I<?>'" or as | |
957 | "magic is enabled if you set C<$Currency> to 'B<[euro]>'", or as | |
958 | "magic is enabled if you set C<$Currency> to '[x20AC]', etc. | |
959 | ||
960 | A Pod formatter may also note, in a comment or warning, a list of what | |
961 | unrenderable characters were encountered. | |
962 | ||
963 | =item * | |
964 | ||
965 | EE<lt>...> may freely appear in any formatting code (other than | |
966 | in another EE<lt>...> or in an ZE<lt>>). That is, "XE<lt>The | |
967 | EE<lt>euro>1,000,000 Solution>" is valid, as is "LE<lt>The | |
968 | EE<lt>euro>1,000,000 Solution|Million::Euros>". | |
969 | ||
970 | =item * | |
971 | ||
972 | Some Pod formatters output to formats that implement nonbreaking | |
973 | spaces as an individual character (which I'll call "NBSP"), and | |
974 | others output to formats that implement nonbreaking spaces just as | |
975 | spaces wrapped in a "don't break this across lines" code. Note that | |
976 | at the level of Pod, both sorts of codes can occur: Pod can contain a | |
977 | NBSP character (whether as a literal, or as a "EE<lt>160>" or | |
978 | "EE<lt>nbsp>" code); and Pod can contain "SE<lt>foo | |
979 | IE<lt>barE<gt> baz>" codes, where "mere spaces" (character 32) in | |
980 | such codes are taken to represent nonbreaking spaces. Pod | |
981 | parsers should consider supporting the optional parsing of "SE<lt>foo | |
982 | IE<lt>barE<gt> baz>" as if it were | |
983 | "fooI<NBSP>IE<lt>barE<gt>I<NBSP>baz", and, going the other way, the | |
984 | optional parsing of groups of words joined by NBSP's as if each group | |
985 | were in a SE<lt>...> code, so that formatters may use the | |
986 | representation that maps best to what the output format demands. | |
987 | ||
988 | =item * | |
989 | ||
210b36aa | 990 | Some processors may find that the C<SE<lt>...E<gt>> code is easiest to |
8a93676d SB |
991 | implement by replacing each space in the parse tree under the content |
992 | of the S, with an NBSP. But note: the replacement should apply I<not> to | |
993 | spaces in I<all> text, but I<only> to spaces in I<printable> text. (This | |
994 | distinction may or may not be evident in the particular tree/event | |
995 | model implemented by the Pod parser.) For example, consider this | |
996 | unusual case: | |
997 | ||
998 | S<L</Autoloaded Functions>> | |
999 | ||
1000 | This means that the space in the middle of the visible link text must | |
1001 | not be broken across lines. In other words, it's the same as this: | |
1002 | ||
1003 | L<"AutoloadedE<160>Functions"/Autoloaded Functions> | |
1004 | ||
1005 | However, a misapplied space-to-NBSP replacement could (wrongly) | |
1006 | produce something equivalent to this: | |
1007 | ||
1008 | L<"AutoloadedE<160>Functions"/AutoloadedE<160>Functions> | |
1009 | ||
1010 | ...which is almost definitely not going to work as a hyperlink (assuming | |
1011 | this formatter outputs a format supporting hypertext). | |
1012 | ||
1013 | Formatters may choose to just not support the S format code, | |
1014 | especially in cases where the output format simply has no NBSP | |
1015 | character/code and no code for "don't break this stuff across lines". | |
1016 | ||
1017 | =item * | |
1018 | ||
1019 | Besides the NBSP character discussed above, implementors are reminded | |
1020 | of the existence of the other "special" character in Latin-1, the | |
210b36aa | 1021 | "soft hyphen" character, also known as "discretionary hyphen", |
8a93676d SB |
1022 | i.e. C<EE<lt>173E<gt>> = C<EE<lt>0xADE<gt>> = |
1023 | C<EE<lt>shyE<gt>>). This character expresses an optional hyphenation | |
1024 | point. That is, it normally renders as nothing, but may render as a | |
1025 | "-" if a formatter breaks the word at that point. Pod formatters | |
1026 | should, as appropriate, do one of the following: 1) render this with | |
1027 | a code with the same meaning (e.g., "\-" in RTF), 2) pass it through | |
1028 | in the expectation that the formatter understands this character as | |
1029 | such, or 3) delete it. | |
1030 | ||
1031 | For example: | |
1032 | ||
1033 | sigE<shy>action | |
1034 | manuE<shy>script | |
1035 | JarkE<shy>ko HieE<shy>taE<shy>nieE<shy>mi | |
1036 | ||
1037 | These signal to a formatter that if it is to hyphenate "sigaction" | |
1038 | or "manuscript", then it should be done as | |
1039 | "sig-I<[linebreak]>action" or "manu-I<[linebreak]>script" | |
1040 | (and if it doesn't hyphenate it, then the C<EE<lt>shyE<gt>> doesn't | |
1041 | show up at all). And if it is | |
1042 | to hyphenate "Jarkko" and/or "Hietaniemi", it can do | |
1043 | so only at the points where there is a C<EE<lt>shyE<gt>> code. | |
1044 | ||
1045 | In practice, it is anticipated that this character will not be used | |
1046 | often, but formatters should either support it, or delete it. | |
1047 | ||
1048 | =item * | |
1049 | ||
1050 | If you think that you want to add a new command to Pod (like, say, a | |
1051 | "=biblio" command), consider whether you could get the same | |
1052 | effect with a for or begin/end sequence: "=for biblio ..." or "=begin | |
1053 | biblio" ... "=end biblio". Pod processors that don't understand | |
1054 | "=for biblio", etc, will simply ignore it, whereas they may complain | |
1055 | loudly if they see "=biblio". | |
1056 | ||
1057 | =item * | |
1058 | ||
1059 | Throughout this document, "Pod" has been the preferred spelling for | |
1060 | the name of the documentation format. One may also use "POD" or | |
da75cd15 | 1061 | "pod". For the documentation that is (typically) in the Pod |
8a93676d SB |
1062 | format, you may use "pod", or "Pod", or "POD". Understanding these |
1063 | distinctions is useful; but obsessing over how to spell them, usually | |
1064 | is not. | |
1065 | ||
1066 | =back | |
1067 | ||
1068 | ||
1069 | ||
1070 | ||
1071 | ||
1072 | =head1 About LE<lt>...E<gt> Codes | |
1073 | ||
1074 | As you can tell from a glance at L<perlpod|perlpod>, the LE<lt>...> | |
1075 | code is the most complex of the Pod formatting codes. The points below | |
1076 | will hopefully clarify what it means and how processors should deal | |
1077 | with it. | |
1078 | ||
1079 | =over | |
1080 | ||
1081 | =item * | |
1082 | ||
1083 | In parsing an LE<lt>...> code, Pod parsers must distinguish at least | |
1084 | four attributes: | |
1085 | ||
1086 | =over | |
1087 | ||
1088 | =item First: | |
1089 | ||
1090 | The link-text. If there is none, this must be undef. (E.g., in | |
1091 | "LE<lt>Perl Functions|perlfunc>", the link-text is "Perl Functions". | |
1092 | In "LE<lt>Time::HiRes>" and even "LE<lt>|Time::HiRes>", there is no | |
1093 | link text. Note that link text may contain formatting.) | |
1094 | ||
1095 | =item Second: | |
1096 | ||
1097 | The possibly inferred link-text -- i.e., if there was no real link | |
1098 | text, then this is the text that we'll infer in its place. (E.g., for | |
1099 | "LE<lt>Getopt::Std>", the inferred link text is "Getopt::Std".) | |
1100 | ||
1101 | =item Third: | |
1102 | ||
1103 | The name or URL, or undef if none. (E.g., in "LE<lt>Perl | |
1104 | Functions|perlfunc>", the name -- also sometimes called the page -- | |
1105 | is "perlfunc". In "LE<lt>/CAVEATS>", the name is undef.) | |
1106 | ||
1107 | =item Fourth: | |
1108 | ||
1109 | The section (AKA "item" in older perlpods), or undef if none. E.g., | |
1110 | in L<Getopt::Std/DESCRIPTION>, "DESCRIPTION" is the section. (Note | |
1111 | that this is not the same as a manpage section like the "5" in "man 5 | |
1112 | crontab". "Section Foo" in the Pod sense means the part of the text | |
6edf2346 | 1113 | that's introduced by the heading or item whose text is "Foo".) |
8a93676d SB |
1114 | |
1115 | =back | |
1116 | ||
1117 | Pod parsers may also note additional attributes including: | |
1118 | ||
1119 | =over | |
1120 | ||
1121 | =item Fifth: | |
1122 | ||
1123 | A flag for whether item 3 (if present) is a URL (like | |
1124 | "http://lists.perl.org" is), in which case there should be no section | |
1125 | attribute; a Pod name (like "perldoc" and "Getopt::Std" are); or | |
1126 | possibly a man page name (like "crontab(5)" is). | |
1127 | ||
1128 | =item Sixth: | |
1129 | ||
1130 | The raw original LE<lt>...> content, before text is split on | |
1131 | "|", "/", etc, and before EE<lt>...> codes are expanded. | |
1132 | ||
1133 | =back | |
1134 | ||
1135 | (The above were numbered only for concise reference below. It is not | |
1136 | a requirement that these be passed as an actual list or array.) | |
1137 | ||
1138 | For example: | |
1139 | ||
1140 | L<Foo::Bar> | |
1141 | => undef, # link text | |
1142 | "Foo::Bar", # possibly inferred link text | |
1143 | "Foo::Bar", # name | |
1144 | undef, # section | |
1145 | 'pod', # what sort of link | |
1146 | "Foo::Bar" # original content | |
1147 | ||
1148 | L<Perlport's section on NL's|perlport/Newlines> | |
1149 | => "Perlport's section on NL's", # link text | |
1150 | "Perlport's section on NL's", # possibly inferred link text | |
1151 | "perlport", # name | |
1152 | "Newlines", # section | |
1153 | 'pod', # what sort of link | |
1154 | "Perlport's section on NL's|perlport/Newlines" # orig. content | |
1155 | ||
1156 | L<perlport/Newlines> | |
1157 | => undef, # link text | |
1158 | '"Newlines" in perlport', # possibly inferred link text | |
1159 | "perlport", # name | |
1160 | "Newlines", # section | |
1161 | 'pod', # what sort of link | |
1162 | "perlport/Newlines" # original content | |
1163 | ||
1164 | L<crontab(5)/"DESCRIPTION"> | |
1165 | => undef, # link text | |
1166 | '"DESCRIPTION" in crontab(5)', # possibly inferred link text | |
1167 | "crontab(5)", # name | |
1168 | "DESCRIPTION", # section | |
1169 | 'man', # what sort of link | |
1170 | 'crontab(5)/"DESCRIPTION"' # original content | |
1171 | ||
1172 | L</Object Attributes> | |
1173 | => undef, # link text | |
1174 | '"Object Attributes"', # possibly inferred link text | |
1175 | undef, # name | |
1176 | "Object Attributes", # section | |
1177 | 'pod', # what sort of link | |
1178 | "/Object Attributes" # original content | |
1179 | ||
1180 | L<http://www.perl.org/> | |
1181 | => undef, # link text | |
1182 | "http://www.perl.org/", # possibly inferred link text | |
1183 | "http://www.perl.org/", # name | |
1184 | undef, # section | |
1185 | 'url', # what sort of link | |
1186 | "http://www.perl.org/" # original content | |
1187 | ||
1188 | Note that you can distinguish URL-links from anything else by the | |
1189 | fact that they match C<m/\A\w+:[^:\s]\S*\z/>. So | |
1190 | C<LE<lt>http://www.perl.comE<gt>> is a URL, but | |
1191 | C<LE<lt>HTTP::ResponseE<gt>> isn't. | |
1192 | ||
1193 | =item * | |
1194 | ||
1195 | In case of LE<lt>...> codes with no "text|" part in them, | |
1196 | older formatters have exhibited great variation in actually displaying | |
1197 | the link or cross reference. For example, LE<lt>crontab(5)> would render | |
1198 | as "the C<crontab(5)> manpage", or "in the C<crontab(5)> manpage" | |
1199 | or just "C<crontab(5)>". | |
1200 | ||
1201 | Pod processors must now treat "text|"-less links as follows: | |
1202 | ||
1203 | L<name> => L<name|name> | |
1204 | L</section> => L<"section"|/section> | |
1205 | L<name/section> => L<"section" in name|name/section> | |
1206 | ||
1207 | =item * | |
1208 | ||
1209 | Note that section names might contain markup. I.e., if a section | |
1210 | starts with: | |
1211 | ||
1212 | =head2 About the C<-M> Operator | |
1213 | ||
1214 | or with: | |
1215 | ||
1216 | =item About the C<-M> Operator | |
1217 | ||
1218 | then a link to it would look like this: | |
1219 | ||
1220 | L<somedoc/About the C<-M> Operator> | |
1221 | ||
1222 | Formatters may choose to ignore the markup for purposes of resolving | |
1223 | the link and use only the renderable characters in the section name, | |
1224 | as in: | |
1225 | ||
1226 | <h1><a name="About_the_-M_Operator">About the <code>-M</code> | |
1227 | Operator</h1> | |
210b36aa | 1228 | |
8a93676d | 1229 | ... |
210b36aa | 1230 | |
8a93676d SB |
1231 | <a href="somedoc#About_the_-M_Operator">About the <code>-M</code> |
1232 | Operator" in somedoc</a> | |
1233 | ||
1234 | =item * | |
1235 | ||
1236 | Previous versions of perlpod distinguished C<LE<lt>name/"section"E<gt>> | |
1237 | links from C<LE<lt>name/itemE<gt>> links (and their targets). These | |
1238 | have been merged syntactically and semantically in the current | |
1239 | specification, and I<section> can refer either to a "=headI<n> Heading | |
1240 | Content" command or to a "=item Item Content" command. This | |
1241 | specification does not specify what behavior should be in the case | |
1242 | of a given document having several things all seeming to produce the | |
1243 | same I<section> identifier (e.g., in HTML, several things all producing | |
1244 | the same I<anchorname> in <a name="I<anchorname>">...</a> | |
1245 | elements). Where Pod processors can control this behavior, they should | |
1246 | use the first such anchor. That is, C<LE<lt>Foo/BarE<gt>> refers to the | |
1247 | I<first> "Bar" section in Foo. | |
1248 | ||
1249 | But for some processors/formats this cannot be easily controlled; as | |
1250 | with the HTML example, the behavior of multiple ambiguous | |
1251 | <a name="I<anchorname>">...</a> is most easily just left up to | |
1252 | browsers to decide. | |
1253 | ||
1254 | =item * | |
1255 | ||
1256 | Authors wanting to link to a particular (absolute) URL, must do so | |
1257 | only with "LE<lt>scheme:...>" codes (like | |
1258 | LE<lt>http://www.perl.org>), and must not attempt "LE<lt>Some Site | |
1259 | Name|scheme:...>" codes. This restriction avoids many problems | |
1260 | in parsing and rendering LE<lt>...> codes. | |
1261 | ||
1262 | =item * | |
1263 | ||
1264 | In a C<LE<lt>text|...E<gt>> code, text may contain formatting codes | |
1265 | for formatting or for EE<lt>...> escapes, as in: | |
1266 | ||
1267 | L<B<ummE<234>stuff>|...> | |
1268 | ||
1269 | For C<LE<lt>...E<gt>> codes without a "name|" part, only | |
1270 | C<EE<lt>...E<gt>> and C<ZE<lt>E<gt>> codes may occur -- no | |
1271 | other formatting codes. That is, authors should not use | |
1272 | "C<LE<lt>BE<lt>Foo::BarE<gt>E<gt>>". | |
1273 | ||
1274 | Note, however, that formatting codes and ZE<lt>>'s can occur in any | |
1275 | and all parts of an LE<lt>...> (i.e., in I<name>, I<section>, I<text>, | |
1276 | and I<url>). | |
1277 | ||
1278 | Authors must not nest LE<lt>...> codes. For example, "LE<lt>The | |
1279 | LE<lt>Foo::Bar> man page>" should be treated as an error. | |
1280 | ||
1281 | =item * | |
1282 | ||
1283 | Note that Pod authors may use formatting codes inside the "text" | |
1284 | part of "LE<lt>text|name>" (and so on for LE<lt>text|/"sec">). | |
1285 | ||
1286 | In other words, this is valid: | |
1287 | ||
1288 | Go read L<the docs on C<$.>|perlvar/"$."> | |
1289 | ||
1290 | Some output formats that do allow rendering "LE<lt>...>" codes as | |
1291 | hypertext, might not allow the link-text to be formatted; in | |
1292 | that case, formatters will have to just ignore that formatting. | |
1293 | ||
1294 | =item * | |
1295 | ||
1296 | At time of writing, C<LE<lt>nameE<gt>> values are of two types: | |
1297 | either the name of a Pod page like C<LE<lt>Foo::BarE<gt>> (which | |
1298 | might be a real Perl module or program in an @INC / PATH | |
1299 | directory, or a .pod file in those places); or the name of a UNIX | |
1300 | man page, like C<LE<lt>crontab(5)E<gt>>. In theory, C<LE<lt>chmodE<gt>> | |
1301 | in ambiguous between a Pod page called "chmod", or the Unix man page | |
1302 | "chmod" (in whatever man-section). However, the presence of a string | |
1303 | in parens, as in "crontab(5)", is sufficient to signal that what | |
1304 | is being discussed is not a Pod page, and so is presumably a | |
1305 | UNIX man page. The distinction is of no importance to many | |
1306 | Pod processors, but some processors that render to hypertext formats | |
1307 | may need to distinguish them in order to know how to render a | |
1308 | given C<LE<lt>fooE<gt>> code. | |
1309 | ||
1310 | =item * | |
1311 | ||
1312 | Previous versions of perlpod allowed for a C<LE<lt>sectionE<gt>> syntax | |
1313 | (as in "C<LE<lt>Object AttributesE<gt>>"), which was not easily distinguishable | |
1314 | from C<LE<lt>nameE<gt>> syntax. This syntax is no longer in the | |
1315 | specification, and has been replaced by the C<LE<lt>"section"E<gt>> syntax | |
1316 | (where the quotes were formerly optional). Pod parsers should tolerate | |
1317 | the C<LE<lt>sectionE<gt>> syntax, for a while at least. The suggested | |
1318 | heuristic for distinguishing C<LE<lt>sectionE<gt>> from C<LE<lt>nameE<gt>> | |
1319 | is that if it contains any whitespace, it's a I<section>. Pod processors | |
1320 | may warn about this being deprecated syntax. | |
1321 | ||
1322 | =back | |
1323 | ||
1324 | =head1 About =over...=back Regions | |
1325 | ||
1326 | "=over"..."=back" regions are used for various kinds of list-like | |
1327 | structures. (I use the term "region" here simply as a collective | |
1328 | term for everything from the "=over" to the matching "=back".) | |
1329 | ||
1330 | =over | |
1331 | ||
1332 | =item * | |
1333 | ||
1334 | The non-zero numeric I<indentlevel> in "=over I<indentlevel>" ... | |
1335 | "=back" is used for giving the formatter a clue as to how many | |
1336 | "spaces" (ems, or roughly equivalent units) it should tab over, | |
1337 | although many formatters will have to convert this to an absolute | |
1338 | measurement that may not exactly match with the size of spaces (or M's) | |
1339 | in the document's base font. Other formatters may have to completely | |
1340 | ignore the number. The lack of any explicit I<indentlevel> parameter is | |
1341 | equivalent to an I<indentlevel> value of 4. Pod processors may | |
1342 | complain if I<indentlevel> is present but is not a positive number | |
1343 | matching C<m/\A(\d*\.)?\d+\z/>. | |
1344 | ||
1345 | =item * | |
1346 | ||
1347 | Authors of Pod formatters are reminded that "=over" ... "=back" may | |
1348 | map to several different constructs in your output format. For | |
1349 | example, in converting Pod to (X)HTML, it can map to any of | |
1350 | <ul>...</ul>, <ol>...</ol>, <dl>...</dl>, or | |
1351 | <blockquote>...</blockquote>. Similarly, "=item" can map to <li> or | |
1352 | <dt>. | |
1353 | ||
1354 | =item * | |
1355 | ||
1356 | Each "=over" ... "=back" region should be one of the following: | |
1357 | ||
1358 | =over | |
1359 | ||
1360 | =item * | |
1361 | ||
1362 | An "=over" ... "=back" region containing only "=item *" commands, | |
1363 | each followed by some number of ordinary/verbatim paragraphs, other | |
1364 | nested "=over" ... "=back" regions, "=for..." paragraphs, and | |
1365 | "=begin"..."=end" regions. | |
1366 | ||
1367 | (Pod processors must tolerate a bare "=item" as if it were "=item | |
1368 | *".) Whether "*" is rendered as a literal asterisk, an "o", or as | |
1369 | some kind of real bullet character, is left up to the Pod formatter, | |
1370 | and may depend on the level of nesting. | |
1371 | ||
1372 | =item * | |
1373 | ||
1374 | An "=over" ... "=back" region containing only | |
1375 | C<m/\A=item\s+\d+\.?\s*\z/> paragraphs, each one (or each group of them) | |
1376 | followed by some number of ordinary/verbatim paragraphs, other nested | |
1377 | "=over" ... "=back" regions, "=for..." paragraphs, and/or | |
1378 | "=begin"..."=end" codes. Note that the numbers must start at 1 | |
1379 | in each section, and must proceed in order and without skipping | |
1380 | numbers. | |
1381 | ||
1382 | (Pod processors must tolerate lines like "=item 1" as if they were | |
1383 | "=item 1.", with the period.) | |
1384 | ||
1385 | =item * | |
1386 | ||
1387 | An "=over" ... "=back" region containing only "=item [text]" | |
1388 | commands, each one (or each group of them) followed by some number of | |
1389 | ordinary/verbatim paragraphs, other nested "=over" ... "=back" | |
1390 | regions, or "=for..." paragraphs, and "=begin"..."=end" regions. | |
1391 | ||
1392 | The "=item [text]" paragraph should not match | |
1393 | C<m/\A=item\s+\d+\.?\s*\z/> or C<m/\A=item\s+\*\s*\z/>, nor should it | |
1394 | match just C<m/\A=item\s*\z/>. | |
1395 | ||
1396 | =item * | |
1397 | ||
1398 | An "=over" ... "=back" region containing no "=item" paragraphs at | |
1399 | all, and containing only some number of | |
1400 | ordinary/verbatim paragraphs, and possibly also some nested "=over" | |
1401 | ... "=back" regions, "=for..." paragraphs, and "=begin"..."=end" | |
1402 | regions. Such an itemless "=over" ... "=back" region in Pod is | |
1403 | equivalent in meaning to a "<blockquote>...</blockquote>" element in | |
1404 | HTML. | |
1405 | ||
1406 | =back | |
1407 | ||
1408 | Note that with all the above cases, you can determine which type of | |
1409 | "=over" ... "=back" you have, by examining the first (non-"=cut", | |
1410 | non-"=pod") Pod paragraph after the "=over" command. | |
1411 | ||
1412 | =item * | |
1413 | ||
1414 | Pod formatters I<must> tolerate arbitrarily large amounts of text | |
1415 | in the "=item I<text...>" paragraph. In practice, most such | |
1416 | paragraphs are short, as in: | |
1417 | ||
1418 | =item For cutting off our trade with all parts of the world | |
1419 | ||
1420 | But they may be arbitrarily long: | |
1421 | ||
1422 | =item For transporting us beyond seas to be tried for pretended | |
1423 | offenses | |
1424 | ||
1425 | =item He is at this time transporting large armies of foreign | |
1426 | mercenaries to complete the works of death, desolation and | |
1427 | tyranny, already begun with circumstances of cruelty and perfidy | |
1428 | scarcely paralleled in the most barbarous ages, and totally | |
1429 | unworthy the head of a civilized nation. | |
1430 | ||
1431 | =item * | |
1432 | ||
1433 | Pod processors should tolerate "=item *" / "=item I<number>" commands | |
1434 | with no accompanying paragraph. The middle item is an example: | |
1435 | ||
1436 | =over | |
210b36aa | 1437 | |
8a93676d | 1438 | =item 1 |
210b36aa | 1439 | |
8a93676d | 1440 | Pick up dry cleaning. |
210b36aa | 1441 | |
8a93676d | 1442 | =item 2 |
210b36aa | 1443 | |
8a93676d | 1444 | =item 3 |
210b36aa | 1445 | |
8a93676d | 1446 | Stop by the store. Get Abba Zabas, Stoli, and cheap lawn chairs. |
210b36aa | 1447 | |
8a93676d SB |
1448 | =back |
1449 | ||
1450 | =item * | |
1451 | ||
1452 | No "=over" ... "=back" region can contain headings. Processors may | |
1453 | treat such a heading as an error. | |
1454 | ||
1455 | =item * | |
1456 | ||
1457 | Note that an "=over" ... "=back" region should have some | |
1458 | content. That is, authors should not have an empty region like this: | |
1459 | ||
1460 | =over | |
210b36aa | 1461 | |
8a93676d SB |
1462 | =back |
1463 | ||
1464 | Pod processors seeing such a contentless "=over" ... "=back" region, | |
1465 | may ignore it, or may report it as an error. | |
1466 | ||
1467 | =item * | |
1468 | ||
1469 | Processors must tolerate an "=over" list that goes off the end of the | |
1470 | document (i.e., which has no matching "=back"), but they may warn | |
1471 | about such a list. | |
1472 | ||
1473 | =item * | |
1474 | ||
1475 | Authors of Pod formatters should note that this construct: | |
1476 | ||
1477 | =item Neque | |
1478 | ||
1479 | =item Porro | |
1480 | ||
1481 | =item Quisquam Est | |
210b36aa | 1482 | |
8a93676d SB |
1483 | Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci |
1484 | velit, sed quia non numquam eius modi tempora incidunt ut | |
1485 | labore et dolore magnam aliquam quaerat voluptatem. | |
1486 | ||
1487 | =item Ut Enim | |
1488 | ||
1489 | is semantically ambiguous, in a way that makes formatting decisions | |
1490 | a bit difficult. On the one hand, it could be mention of an item | |
1491 | "Neque", mention of another item "Porro", and mention of another | |
1492 | item "Quisquam Est", with just the last one requiring the explanatory | |
1493 | paragraph "Qui dolorem ipsum quia dolor..."; and then an item | |
1494 | "Ut Enim". In that case, you'd want to format it like so: | |
1495 | ||
1496 | Neque | |
210b36aa | 1497 | |
8a93676d | 1498 | Porro |
210b36aa | 1499 | |
8a93676d SB |
1500 | Quisquam Est |
1501 | Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci | |
1502 | velit, sed quia non numquam eius modi tempora incidunt ut | |
1503 | labore et dolore magnam aliquam quaerat voluptatem. | |
1504 | ||
1505 | Ut Enim | |
1506 | ||
1507 | But it could equally well be a discussion of three (related or equivalent) | |
1508 | items, "Neque", "Porro", and "Quisquam Est", followed by a paragraph | |
1509 | explaining them all, and then a new item "Ut Enim". In that case, you'd | |
1510 | probably want to format it like so: | |
1511 | ||
1512 | Neque | |
1513 | Porro | |
1514 | Quisquam Est | |
1515 | Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci | |
1516 | velit, sed quia non numquam eius modi tempora incidunt ut | |
1517 | labore et dolore magnam aliquam quaerat voluptatem. | |
1518 | ||
1519 | Ut Enim | |
1520 | ||
1521 | But (for the forseeable future), Pod does not provide any way for Pod | |
1522 | authors to distinguish which grouping is meant by the above | |
1523 | "=item"-cluster structure. So formatters should format it like so: | |
1524 | ||
1525 | Neque | |
1526 | ||
1527 | Porro | |
1528 | ||
1529 | Quisquam Est | |
1530 | ||
1531 | Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci | |
1532 | velit, sed quia non numquam eius modi tempora incidunt ut | |
1533 | labore et dolore magnam aliquam quaerat voluptatem. | |
1534 | ||
1535 | Ut Enim | |
1536 | ||
210b36aa | 1537 | That is, there should be (at least roughly) equal spacing between |
8a93676d SB |
1538 | items as between paragraphs (although that spacing may well be less |
1539 | than the full height of a line of text). This leaves it to the reader | |
1540 | to use (con)textual cues to figure out whether the "Qui dolorem | |
1541 | ipsum..." paragraph applies to the "Quisquam Est" item or to all three | |
1542 | items "Neque", "Porro", and "Quisquam Est". While not an ideal | |
1543 | situation, this is preferable to providing formatting cues that may | |
1544 | be actually contrary to the author's intent. | |
1545 | ||
1546 | =back | |
1547 | ||
1548 | ||
1549 | ||
1550 | =head1 About Data Paragraphs and "=begin/=end" Regions | |
1551 | ||
1552 | Data paragraphs are typically used for inlining non-Pod data that is | |
1553 | to be used (typically passed through) when rendering the document to | |
1554 | a specific format: | |
1555 | ||
1556 | =begin rtf | |
210b36aa | 1557 | |
8a93676d | 1558 | \par{\pard\qr\sa4500{\i Printed\~\chdate\~\chtime}\par} |
210b36aa | 1559 | |
8a93676d SB |
1560 | =end rtf |
1561 | ||
1562 | The exact same effect could, incidentally, be achieved with a single | |
1563 | "=for" paragraph: | |
1564 | ||
1565 | =for rtf \par{\pard\qr\sa4500{\i Printed\~\chdate\~\chtime}\par} | |
1566 | ||
1567 | (Although that is not formally a data paragraph, it has the same | |
1568 | meaning as one, and Pod parsers may parse it as one.) | |
1569 | ||
1570 | Another example of a data paragraph: | |
1571 | ||
1572 | =begin html | |
210b36aa | 1573 | |
8a93676d | 1574 | I like <em>PIE</em>! |
210b36aa | 1575 | |
8a93676d | 1576 | <hr>Especially pecan pie! |
210b36aa | 1577 | |
8a93676d SB |
1578 | =end html |
1579 | ||
1580 | If these were ordinary paragraphs, the Pod parser would try to | |
1581 | expand the "EE<lt>/em>" (in the first paragraph) as a formatting | |
1582 | code, just like "EE<lt>lt>" or "EE<lt>eacute>". But since this | |
1583 | is in a "=begin I<identifier>"..."=end I<identifier>" region I<and> | |
1584 | the identifier "html" doesn't begin have a ":" prefix, the contents | |
1585 | of this region are stored as data paragraphs, instead of being | |
1586 | processed as ordinary paragraphs (or if they began with a spaces | |
1587 | and/or tabs, as verbatim paragraphs). | |
1588 | ||
1589 | As a further example: At time of writing, no "biblio" identifier is | |
1590 | supported, but suppose some processor were written to recognize it as | |
1591 | a way of (say) denoting a bibliographic reference (necessarily | |
1592 | containing formatting codes in ordinary paragraphs). The fact that | |
1593 | "biblio" paragraphs were meant for ordinary processing would be | |
1594 | indicated by prefacing each "biblio" identifier with a colon: | |
1595 | ||
1596 | =begin :biblio | |
1597 | ||
1598 | Wirth, Niklaus. 1976. I<Algorithms + Data Structures = | |
1599 | Programs.> Prentice-Hall, Englewood Cliffs, NJ. | |
1600 | ||
1601 | =end :biblio | |
1602 | ||
1603 | This would signal to the parser that paragraphs in this begin...end | |
1604 | region are subject to normal handling as ordinary/verbatim paragraphs | |
1605 | (while still tagged as meant only for processors that understand the | |
1606 | "biblio" identifier). The same effect could be had with: | |
1607 | ||
1608 | =for :biblio | |
1609 | Wirth, Niklaus. 1976. I<Algorithms + Data Structures = | |
1610 | Programs.> Prentice-Hall, Englewood Cliffs, NJ. | |
1611 | ||
1612 | The ":" on these identifiers means simply "process this stuff | |
1613 | normally, even though the result will be for some special target". | |
1614 | I suggest that parser APIs report "biblio" as the target identifier, | |
1615 | but also report that it had a ":" prefix. (And similarly, with the | |
1616 | above "html", report "html" as the target identifier, and note the | |
1617 | I<lack> of a ":" prefix.) | |
1618 | ||
1619 | Note that a "=begin I<identifier>"..."=end I<identifier>" region where | |
1620 | I<identifier> begins with a colon, I<can> contain commands. For example: | |
1621 | ||
1622 | =begin :biblio | |
210b36aa | 1623 | |
8a93676d | 1624 | Wirth's classic is available in several editions, including: |
210b36aa | 1625 | |
8a93676d SB |
1626 | =for comment |
1627 | hm, check abebooks.com for how much used copies cost. | |
210b36aa | 1628 | |
8a93676d | 1629 | =over |
210b36aa | 1630 | |
8a93676d | 1631 | =item |
210b36aa | 1632 | |
8a93676d SB |
1633 | Wirth, Niklaus. 1975. I<Algorithmen und Datenstrukturen.> |
1634 | Teubner, Stuttgart. [Yes, it's in German.] | |
210b36aa | 1635 | |
8a93676d | 1636 | =item |
210b36aa | 1637 | |
8a93676d SB |
1638 | Wirth, Niklaus. 1976. I<Algorithms + Data Structures = |
1639 | Programs.> Prentice-Hall, Englewood Cliffs, NJ. | |
210b36aa | 1640 | |
8a93676d | 1641 | =back |
210b36aa | 1642 | |
8a93676d SB |
1643 | =end :biblio |
1644 | ||
1645 | Note, however, a "=begin I<identifier>"..."=end I<identifier>" | |
1646 | region where I<identifier> does I<not> begin with a colon, should not | |
1647 | directly contain "=head1" ... "=head4" commands, nor "=over", nor "=back", | |
1648 | nor "=item". For example, this may be considered invalid: | |
1649 | ||
1650 | =begin somedata | |
210b36aa | 1651 | |
8a93676d | 1652 | This is a data paragraph. |
210b36aa | 1653 | |
8a93676d | 1654 | =head1 Don't do this! |
210b36aa | 1655 | |
8a93676d | 1656 | This is a data paragraph too. |
210b36aa | 1657 | |
8a93676d SB |
1658 | =end somedata |
1659 | ||
1660 | A Pod processor may signal that the above (specifically the "=head1" | |
1661 | paragraph) is an error. Note, however, that the following should | |
1662 | I<not> be treated as an error: | |
1663 | ||
1664 | =begin somedata | |
210b36aa | 1665 | |
8a93676d | 1666 | This is a data paragraph. |
210b36aa | 1667 | |
8a93676d | 1668 | =cut |
210b36aa | 1669 | |
8a93676d SB |
1670 | # Yup, this isn't Pod anymore. |
1671 | sub excl { (rand() > .5) ? "hoo!" : "hah!" } | |
210b36aa | 1672 | |
8a93676d | 1673 | =pod |
210b36aa | 1674 | |
8a93676d | 1675 | This is a data paragraph too. |
210b36aa | 1676 | |
8a93676d SB |
1677 | =end somedata |
1678 | ||
1679 | And this too is valid: | |
1680 | ||
1681 | =begin someformat | |
210b36aa | 1682 | |
8a93676d | 1683 | This is a data paragraph. |
210b36aa | 1684 | |
8a93676d | 1685 | And this is a data paragraph. |
210b36aa | 1686 | |
8a93676d | 1687 | =begin someotherformat |
210b36aa | 1688 | |
8a93676d | 1689 | This is a data paragraph too. |
210b36aa | 1690 | |
8a93676d | 1691 | And this is a data paragraph too. |
210b36aa | 1692 | |
8a93676d SB |
1693 | =begin :yetanotherformat |
1694 | ||
1695 | =head2 This is a command paragraph! | |
1696 | ||
1697 | This is an ordinary paragraph! | |
210b36aa | 1698 | |
8a93676d | 1699 | And this is a verbatim paragraph! |
210b36aa | 1700 | |
8a93676d | 1701 | =end :yetanotherformat |
210b36aa | 1702 | |
8a93676d | 1703 | =end someotherformat |
210b36aa | 1704 | |
8a93676d | 1705 | Another data paragraph! |
210b36aa | 1706 | |
8a93676d SB |
1707 | =end someformat |
1708 | ||
1709 | The contents of the above "=begin :yetanotherformat" ... | |
1710 | "=end :yetanotherformat" region I<aren't> data paragraphs, because | |
1711 | the immediately containing region's identifier (":yetanotherformat") | |
1712 | begins with a colon. In practice, most regions that contain | |
1713 | data paragraphs will contain I<only> data paragraphs; however, | |
1714 | the above nesting is syntactically valid as Pod, even if it is | |
1715 | rare. However, the handlers for some formats, like "html", | |
1716 | will accept only data paragraphs, not nested regions; and they may | |
1717 | complain if they see (targeted for them) nested regions, or commands, | |
1718 | other than "=end", "=pod", and "=cut". | |
1719 | ||
1720 | Also consider this valid structure: | |
1721 | ||
1722 | =begin :biblio | |
210b36aa | 1723 | |
8a93676d | 1724 | Wirth's classic is available in several editions, including: |
210b36aa | 1725 | |
8a93676d | 1726 | =over |
210b36aa | 1727 | |
8a93676d | 1728 | =item |
210b36aa | 1729 | |
8a93676d SB |
1730 | Wirth, Niklaus. 1975. I<Algorithmen und Datenstrukturen.> |
1731 | Teubner, Stuttgart. [Yes, it's in German.] | |
210b36aa | 1732 | |
8a93676d | 1733 | =item |
210b36aa | 1734 | |
8a93676d SB |
1735 | Wirth, Niklaus. 1976. I<Algorithms + Data Structures = |
1736 | Programs.> Prentice-Hall, Englewood Cliffs, NJ. | |
1737 | ||
1738 | =back | |
210b36aa | 1739 | |
8a93676d | 1740 | Buy buy buy! |
210b36aa | 1741 | |
8a93676d | 1742 | =begin html |
210b36aa | 1743 | |
8a93676d | 1744 | <img src='wirth_spokesmodeling_book.png'> |
210b36aa | 1745 | |
8a93676d | 1746 | <hr> |
210b36aa | 1747 | |
8a93676d | 1748 | =end html |
210b36aa | 1749 | |
8a93676d | 1750 | Now now now! |
210b36aa | 1751 | |
8a93676d SB |
1752 | =end :biblio |
1753 | ||
1754 | There, the "=begin html"..."=end html" region is nested inside | |
1755 | the larger "=begin :biblio"..."=end :biblio" region. Note that the | |
1756 | content of the "=begin html"..."=end html" region is data | |
1757 | paragraph(s), because the immediately containing region's identifier | |
1758 | ("html") I<doesn't> begin with a colon. | |
1759 | ||
1760 | Pod parsers, when processing a series of data paragraphs one | |
1761 | after another (within a single region), should consider them to | |
1762 | be one large data paragraph that happens to contain blank lines. So | |
1763 | the content of the above "=begin html"..."=end html" I<may> be stored | |
1764 | as two data paragraphs (one consisting of | |
1765 | "<img src='wirth_spokesmodeling_book.png'>\n" | |
1766 | and another consisting of "<hr>\n"), but I<should> be stored as | |
1767 | a single data paragraph (consisting of | |
1768 | "<img src='wirth_spokesmodeling_book.png'>\n\n<hr>\n"). | |
1769 | ||
1770 | Pod processors should tolerate empty | |
1771 | "=begin I<something>"..."=end I<something>" regions, | |
1772 | empty "=begin :I<something>"..."=end :I<something>" regions, and | |
1773 | contentless "=for I<something>" and "=for :I<something>" | |
1774 | paragraphs. I.e., these should be tolerated: | |
1775 | ||
1776 | =for html | |
210b36aa | 1777 | |
8a93676d | 1778 | =begin html |
210b36aa | 1779 | |
8a93676d | 1780 | =end html |
210b36aa | 1781 | |
8a93676d | 1782 | =begin :biblio |
210b36aa | 1783 | |
8a93676d SB |
1784 | =end :biblio |
1785 | ||
1786 | Incidentally, note that there's no easy way to express a data | |
1787 | paragraph starting with something that looks like a command. Consider: | |
1788 | ||
1789 | =begin stuff | |
210b36aa | 1790 | |
8a93676d | 1791 | =shazbot |
210b36aa | 1792 | |
8a93676d SB |
1793 | =end stuff |
1794 | ||
1795 | There, "=shazbot" will be parsed as a Pod command "shazbot", not as a data | |
1796 | paragraph "=shazbot\n". However, you can express a data paragraph consisting | |
1797 | of "=shazbot\n" using this code: | |
1798 | ||
1799 | =for stuff =shazbot | |
1800 | ||
1801 | The situation where this is necessary, is presumably quite rare. | |
1802 | ||
1803 | Note that =end commands must match the currently open =begin command. That | |
1804 | is, they must properly nest. For example, this is valid: | |
1805 | ||
1806 | =begin outer | |
210b36aa | 1807 | |
8a93676d | 1808 | X |
210b36aa | 1809 | |
8a93676d | 1810 | =begin inner |
210b36aa | 1811 | |
8a93676d | 1812 | Y |
210b36aa | 1813 | |
8a93676d | 1814 | =end inner |
210b36aa | 1815 | |
8a93676d | 1816 | Z |
210b36aa | 1817 | |
8a93676d SB |
1818 | =end outer |
1819 | ||
1820 | while this is invalid: | |
1821 | ||
1822 | =begin outer | |
210b36aa | 1823 | |
8a93676d | 1824 | X |
210b36aa | 1825 | |
8a93676d | 1826 | =begin inner |
210b36aa | 1827 | |
8a93676d | 1828 | Y |
210b36aa | 1829 | |
8a93676d | 1830 | =end outer |
210b36aa | 1831 | |
8a93676d | 1832 | Z |
210b36aa | 1833 | |
8a93676d | 1834 | =end inner |
210b36aa | 1835 | |
8a93676d SB |
1836 | This latter is improper because when the "=end outer" command is seen, the |
1837 | currently open region has the formatname "inner", not "outer". (It just | |
1838 | happens that "outer" is the format name of a higher-up region.) This is | |
1839 | an error. Processors must by default report this as an error, and may halt | |
210b36aa | 1840 | processing the document containing that error. A corollary of this is that |
8a93676d SB |
1841 | regions cannot "overlap" -- i.e., the latter block above does not represent |
1842 | a region called "outer" which contains X and Y, overlapping a region called | |
1843 | "inner" which contains Y and Z. But because it is invalid (as all | |
1844 | apparently overlapping regions would be), it doesn't represent that, or | |
1845 | anything at all. | |
1846 | ||
1847 | Similarly, this is invalid: | |
1848 | ||
1849 | =begin thing | |
210b36aa | 1850 | |
8a93676d SB |
1851 | =end hting |
1852 | ||
1853 | This is an error because the region is opened by "thing", and the "=end" | |
1854 | tries to close "hting" [sic]. | |
1855 | ||
1856 | This is also invalid: | |
1857 | ||
1858 | =begin thing | |
210b36aa | 1859 | |
8a93676d SB |
1860 | =end |
1861 | ||
1862 | This is invalid because every "=end" command must have a formatname | |
1863 | parameter. | |
1864 | ||
1865 | =head1 SEE ALSO | |
1866 | ||
1867 | L<perlpod>, L<perlsyn/"PODs: Embedded Documentation">, | |
1868 | L<podchecker> | |
1869 | ||
1870 | =head1 AUTHOR | |
1871 | ||
1872 | Sean M. Burke | |
1873 | ||
1874 | =cut | |
1875 | ||
1876 |