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1 | |
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 | ||
ac036724 | 33 | Pod is embedded in files, typically Perl source files, although you |
8a93676d SB |
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 | |
ac036724 | 52 | spaces/tabs and then a newline as a blank line. The only lines they |
8a93676d SB |
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 | |
353c6505 | 68 | else with the Pod (like counting words, scanning for index points, |
8a93676d SB |
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 | |
ac036724 | 73 | that matches C<m/\A=cut/> or up to the end of the file if there is |
8a93676d SB |
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 | |
ac036724 | 135 | would to an ordinary paragraph (i.e., formatting codes like |
8a93676d SB |
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 | |
6fbdb1cc | 192 | paragraphs that they surround from being parsed as ordinary or verbatim |
8a93676d SB |
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 | ||
659cfd94 | 241 | It is an error to try to I<start> a Pod block with a "=cut" command. In |
8a93676d SB |
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 | ||
93592fd5 RS |
296 | =item "=begin formatname parameter" |
297 | ||
8a93676d SB |
298 | This marks the following paragraphs (until the matching "=end |
299 | formatname") as being for some special kind of processing. Unless | |
300 | "formatname" begins with a colon, the contained non-command | |
301 | paragraphs are data paragraphs. But if "formatname" I<does> begin | |
302 | with a colon, then non-command paragraphs are ordinary paragraphs | |
303 | or data paragraphs. This is discussed in detail in the section | |
304 | L</About Data Paragraphs and "=beginE<sol>=end" Regions>. | |
305 | ||
306 | It is advised that formatnames match the regexp | |
93592fd5 RS |
307 | C<m/\A:?[−a−zA−Z0−9_]+\z/>. Everything following whitespace after the |
308 | formatname is a parameter that may be used by the formatter when dealing | |
309 | with this region. This parameter must not be repeated in the "=end" | |
310 | paragraph. Implementors should anticipate future expansion in the | |
311 | semantics and syntax of the first parameter to "=begin"/"=end"/"=for". | |
8a93676d SB |
312 | |
313 | =item "=end formatname" | |
314 | ||
315 | This marks the end of the region opened by the matching | |
316 | "=begin formatname" region. If "formatname" is not the formatname | |
317 | of the most recent open "=begin formatname" region, then this | |
318 | is an error, and must generate an error message. This | |
319 | is discussed in detail in the section | |
320 | L</About Data Paragraphs and "=beginE<sol>=end" Regions>. | |
321 | ||
322 | =item "=for formatname text..." | |
323 | ||
324 | This is synonymous with: | |
325 | ||
326 | =begin formatname | |
210b36aa | 327 | |
8a93676d | 328 | text... |
210b36aa | 329 | |
8a93676d SB |
330 | =end formatname |
331 | ||
332 | That is, it creates a region consisting of a single paragraph; that | |
333 | paragraph is to be treated as a normal paragraph if "formatname" | |
334 | begins with a ":"; if "formatname" I<doesn't> begin with a colon, | |
335 | then "text..." will constitute a data paragraph. There is no way | |
336 | to use "=for formatname text..." to express "text..." as a verbatim | |
337 | paragraph. | |
338 | ||
a179871b SB |
339 | =item "=encoding encodingname" |
340 | ||
341 | This command, which should occur early in the document (at least | |
1e54db1a | 342 | before any non-US-ASCII data!), declares that this document is |
a179871b | 343 | encoded in the encoding I<encodingname>, which must be |
6fbdb1cc | 344 | an encoding name that L<Encode> recognizes. (Encode's list |
8a3f7e95 | 345 | of supported encodings, in L<Encode::Supported>, is useful here.) |
a179871b SB |
346 | If the Pod parser cannot decode the declared encoding, it |
347 | should emit a warning and may abort parsing the document | |
348 | altogether. | |
349 | ||
350 | A document having more than one "=encoding" line should be | |
351 | considered an error. Pod processors may silently tolerate this if | |
352 | the not-first "=encoding" lines are just duplicates of the | |
6fbdb1cc RS |
353 | first one (e.g., if there's a "=encoding utf8" line, and later on |
354 | another "=encoding utf8" line). But Pod processors should complain if | |
a179871b SB |
355 | there are contradictory "=encoding" lines in the same document |
356 | (e.g., if there is a "=encoding utf8" early in the document and | |
357 | "=encoding big5" later). Pod processors that recognize BOMs | |
358 | may also complain if they see an "=encoding" line | |
1e54db1a JH |
359 | that contradicts the BOM (e.g., if a document with a UTF-16LE |
360 | BOM has an "=encoding shiftjis" line). | |
a179871b | 361 | |
8a93676d SB |
362 | =back |
363 | ||
364 | If a Pod processor sees any command other than the ones listed | |
365 | above (like "=head", or "=haed1", or "=stuff", or "=cuttlefish", | |
366 | or "=w123"), that processor must by default treat this as an | |
367 | error. It must not process the paragraph beginning with that | |
368 | command, must by default warn of this as an error, and may | |
369 | abort the parse. A Pod parser may allow a way for particular | |
370 | applications to add to the above list of known commands, and to | |
371 | stipulate, for each additional command, whether formatting | |
372 | codes should be processed. | |
373 | ||
374 | Future versions of this specification may add additional | |
375 | commands. | |
376 | ||
377 | ||
378 | ||
379 | =head1 Pod Formatting Codes | |
380 | ||
381 | (Note that in previous drafts of this document and of perlpod, | |
382 | formatting codes were referred to as "interior sequences", and | |
383 | this term may still be found in the documentation for Pod parsers, | |
384 | and in error messages from Pod processors.) | |
385 | ||
386 | There are two syntaxes for formatting codes: | |
387 | ||
388 | =over | |
389 | ||
390 | =item * | |
391 | ||
392 | A formatting code starts with a capital letter (just US-ASCII [A-Z]) | |
393 | followed by a "<", any number of characters, and ending with the first | |
394 | matching ">". Examples: | |
395 | ||
396 | That's what I<you> think! | |
397 | ||
398 | What's C<dump()> for? | |
399 | ||
400 | X<C<chmod> and C<unlink()> Under Different Operating Systems> | |
401 | ||
402 | =item * | |
403 | ||
404 | A formatting code starts with a capital letter (just US-ASCII [A-Z]) | |
405 | followed by two or more "<"'s, one or more whitespace characters, | |
406 | any number of characters, one or more whitespace characters, | |
407 | and ending with the first matching sequence of two or more ">"'s, where | |
408 | the number of ">"'s equals the number of "<"'s in the opening of this | |
409 | formatting code. Examples: | |
410 | ||
411 | That's what I<< you >> think! | |
412 | ||
413 | C<<< open(X, ">>thing.dat") || die $! >>> | |
414 | ||
415 | B<< $foo->bar(); >> | |
416 | ||
417 | With this syntax, the whitespace character(s) after the "CE<lt><<" | |
ac036724 | 418 | and before the ">>" (or whatever letter) are I<not> renderable. They |
8a93676d SB |
419 | do not signify whitespace, are merely part of the formatting codes |
420 | themselves. That is, these are all synonymous: | |
421 | ||
422 | C<thing> | |
423 | C<< thing >> | |
424 | C<< thing >> | |
425 | C<<< thing >>> | |
426 | C<<<< | |
427 | thing | |
428 | >>>> | |
429 | ||
430 | and so on. | |
431 | ||
432 | =back | |
433 | ||
434 | In parsing Pod, a notably tricky part is the correct parsing of | |
435 | (potentially nested!) formatting codes. Implementors should | |
436 | consult the code in the C<parse_text> routine in Pod::Parser as an | |
437 | example of a correct implementation. | |
438 | ||
439 | =over | |
440 | ||
441 | =item C<IE<lt>textE<gt>> -- italic text | |
442 | ||
443 | See the brief discussion in L<perlpod/"Formatting Codes">. | |
444 | ||
445 | =item C<BE<lt>textE<gt>> -- bold text | |
446 | ||
447 | See the brief discussion in L<perlpod/"Formatting Codes">. | |
448 | ||
449 | =item C<CE<lt>codeE<gt>> -- code text | |
450 | ||
451 | See the brief discussion in L<perlpod/"Formatting Codes">. | |
452 | ||
453 | =item C<FE<lt>filenameE<gt>> -- style for filenames | |
454 | ||
455 | See the brief discussion in L<perlpod/"Formatting Codes">. | |
456 | ||
457 | =item C<XE<lt>topic nameE<gt>> -- an index entry | |
458 | ||
459 | See the brief discussion in L<perlpod/"Formatting Codes">. | |
460 | ||
461 | This code is unusual in that most formatters completely discard | |
462 | this code and its content. Other formatters will render it with | |
463 | invisible codes that can be used in building an index of | |
464 | the current document. | |
465 | ||
466 | =item C<ZE<lt>E<gt>> -- a null (zero-effect) formatting code | |
467 | ||
468 | Discussed briefly in L<perlpod/"Formatting Codes">. | |
469 | ||
470 | This code is unusual is that it should have no content. That is, | |
471 | a processor may complain if it sees C<ZE<lt>potatoesE<gt>>. Whether | |
472 | or not it complains, the I<potatoes> text should ignored. | |
473 | ||
474 | =item C<LE<lt>nameE<gt>> -- a hyperlink | |
475 | ||
476 | The complicated syntaxes of this code are discussed at length in | |
477 | L<perlpod/"Formatting Codes">, and implementation details are | |
478 | discussed below, in L</"About LE<lt>...E<gt> Codes">. Parsing the | |
479 | contents of LE<lt>content> is tricky. Notably, the content has to be | |
480 | checked for whether it looks like a URL, or whether it has to be split | |
481 | on literal "|" and/or "/" (in the right order!), and so on, | |
482 | I<before> EE<lt>...> codes are resolved. | |
483 | ||
484 | =item C<EE<lt>escapeE<gt>> -- a character escape | |
485 | ||
486 | See L<perlpod/"Formatting Codes">, and several points in | |
487 | L</Notes on Implementing Pod Processors>. | |
488 | ||
489 | =item C<SE<lt>textE<gt>> -- text contains non-breaking spaces | |
490 | ||
491 | This formatting code is syntactically simple, but semantically | |
492 | complex. What it means is that each space in the printable | |
3e666715 | 493 | content of this code signifies a non-breaking space. |
8a93676d SB |
494 | |
495 | Consider: | |
496 | ||
497 | C<$x ? $y : $z> | |
498 | ||
499 | S<C<$x ? $y : $z>> | |
500 | ||
501 | Both signify the monospace (c[ode] style) text consisting of | |
502 | "$x", one space, "?", one space, ":", one space, "$z". The | |
503 | difference is that in the latter, with the S code, those spaces | |
3e666715 | 504 | are not "normal" spaces, but instead are non-breaking spaces. |
8a93676d SB |
505 | |
506 | =back | |
507 | ||
508 | ||
509 | If a Pod processor sees any formatting code other than the ones | |
510 | listed above (as in "NE<lt>...>", or "QE<lt>...>", etc.), that | |
511 | processor must by default treat this as an error. | |
512 | A Pod parser may allow a way for particular | |
513 | applications to add to the above list of known formatting codes; | |
514 | a Pod parser might even allow a way to stipulate, for each additional | |
515 | command, whether it requires some form of special processing, as | |
516 | LE<lt>...> does. | |
517 | ||
518 | Future versions of this specification may add additional | |
519 | formatting codes. | |
520 | ||
521 | Historical note: A few older Pod processors would not see a ">" as | |
522 | closing a "CE<lt>" code, if the ">" was immediately preceded by | |
523 | a "-". This was so that this: | |
524 | ||
525 | C<$foo->bar> | |
526 | ||
527 | would parse as equivalent to this: | |
528 | ||
75f15e9f | 529 | C<$foo-E<gt>bar> |
8a93676d SB |
530 | |
531 | instead of as equivalent to a "C" formatting code containing | |
532 | only "$foo-", and then a "bar>" outside the "C" formatting code. This | |
533 | problem has since been solved by the addition of syntaxes like this: | |
534 | ||
535 | C<< $foo->bar >> | |
536 | ||
537 | Compliant parsers must not treat "->" as special. | |
538 | ||
539 | Formatting codes absolutely cannot span paragraphs. If a code is | |
540 | opened in one paragraph, and no closing code is found by the end of | |
541 | that paragraph, the Pod parser must close that formatting code, | |
542 | and should complain (as in "Unterminated I code in the paragraph | |
543 | starting at line 123: 'Time objects are not...'"). So these | |
544 | two paragraphs: | |
545 | ||
546 | I<I told you not to do this! | |
210b36aa | 547 | |
8a93676d SB |
548 | Don't make me say it again!> |
549 | ||
550 | ...must I<not> be parsed as two paragraphs in italics (with the I | |
551 | code starting in one paragraph and starting in another.) Instead, | |
552 | the first paragraph should generate a warning, but that aside, the | |
553 | above code must parse as if it were: | |
554 | ||
555 | I<I told you not to do this!> | |
210b36aa | 556 | |
8a93676d SB |
557 | Don't make me say it again!E<gt> |
558 | ||
559 | (In SGMLish jargon, all Pod commands are like block-level | |
560 | elements, whereas all Pod formatting codes are like inline-level | |
561 | elements.) | |
562 | ||
563 | ||
564 | ||
565 | =head1 Notes on Implementing Pod Processors | |
566 | ||
567 | The following is a long section of miscellaneous requirements | |
568 | and suggestions to do with Pod processing. | |
569 | ||
570 | =over | |
571 | ||
572 | =item * | |
573 | ||
574 | Pod formatters should tolerate lines in verbatim blocks that are of | |
575 | any length, even if that means having to break them (possibly several | |
576 | times, for very long lines) to avoid text running off the side of the | |
577 | page. Pod formatters may warn of such line-breaking. Such warnings | |
578 | are particularly appropriate for lines are over 100 characters long, which | |
579 | are usually not intentional. | |
580 | ||
581 | =item * | |
582 | ||
583 | Pod parsers must recognize I<all> of the three well-known newline | |
584 | formats: CR, LF, and CRLF. See L<perlport|perlport>. | |
585 | ||
586 | =item * | |
587 | ||
588 | Pod parsers should accept input lines that are of any length. | |
589 | ||
590 | =item * | |
591 | ||
592 | Since Perl recognizes a Unicode Byte Order Mark at the start of files | |
593 | as signaling that the file is Unicode encoded as in UTF-16 (whether | |
594 | big-endian or little-endian) or UTF-8, Pod parsers should do the | |
595 | same. Otherwise, the character encoding should be understood as | |
596 | being UTF-8 if the first highbit byte sequence in the file seems | |
597 | valid as a UTF-8 sequence, or otherwise as Latin-1. | |
598 | ||
599 | Future versions of this specification may specify | |
600 | how Pod can accept other encodings. Presumably treatment of other | |
601 | encodings in Pod parsing would be as in XML parsing: whatever the | |
602 | encoding declared by a particular Pod file, content is to be | |
603 | stored in memory as Unicode characters. | |
604 | ||
605 | =item * | |
606 | ||
607 | The well known Unicode Byte Order Marks are as follows: if the | |
608 | file begins with the two literal byte values 0xFE 0xFF, this is | |
609 | the BOM for big-endian UTF-16. If the file begins with the two | |
610 | literal byte value 0xFF 0xFE, this is the BOM for little-endian | |
611 | UTF-16. If the file begins with the three literal byte values | |
612 | 0xEF 0xBB 0xBF, this is the BOM for UTF-8. | |
613 | ||
614 | =for comment | |
615 | use bytes; print map sprintf(" 0x%02X", ord $_), split '', "\x{feff}"; | |
616 | 0xEF 0xBB 0xBF | |
617 | ||
618 | =for comment | |
1e54db1a | 619 | If toke.c is modified to support UTF-32, add mention of those here. |
8a93676d SB |
620 | |
621 | =item * | |
622 | ||
623 | A naive but sufficient heuristic for testing the first highbit | |
624 | byte-sequence in a BOM-less file (whether in code or in Pod!), to see | |
625 | whether that sequence is valid as UTF-8 (RFC 2279) is to check whether | |
626 | that the first byte in the sequence is in the range 0xC0 - 0xFD | |
627 | I<and> whether the next byte is in the range | |
628 | 0x80 - 0xBF. If so, the parser may conclude that this file is in | |
629 | UTF-8, and all highbit sequences in the file should be assumed to | |
630 | be UTF-8. Otherwise the parser should treat the file as being | |
631 | in Latin-1. In the unlikely circumstance that the first highbit | |
632 | sequence in a truly non-UTF-8 file happens to appear to be UTF-8, one | |
633 | can cater to our heuristic (as well as any more intelligent heuristic) | |
634 | by prefacing that line with a comment line containing a highbit | |
635 | sequence that is clearly I<not> valid as UTF-8. A line consisting | |
636 | of simply "#", an e-acute, and any non-highbit byte, | |
637 | is sufficient to establish this file's encoding. | |
638 | ||
639 | =for comment | |
640 | If/WHEN some brave soul makes these heuristics into a generic | |
fae2c0fb | 641 | text-file class (or PerlIO layer?), we can presumably delete |
8a93676d | 642 | mention of these icky details from this file, and can instead |
fae2c0fb | 643 | tell people to just use appropriate class/layer. |
8a93676d | 644 | Auto-recognition of newline sequences would be another desirable |
fae2c0fb | 645 | feature of such a class/layer. |
8a93676d SB |
646 | HINT HINT HINT. |
647 | ||
648 | =for comment | |
649 | "The probability that a string of characters | |
650 | in any other encoding appears as valid UTF-8 is low" - RFC2279 | |
651 | ||
652 | =item * | |
653 | ||
654 | This document's requirements and suggestions about encodings | |
655 | do not apply to Pod processors running on non-ASCII platforms, | |
656 | notably EBCDIC platforms. | |
657 | ||
658 | =item * | |
659 | ||
660 | Pod processors must treat a "=for [label] [content...]" paragraph as | |
661 | meaning the same thing as a "=begin [label]" paragraph, content, and | |
662 | an "=end [label]" paragraph. (The parser may conflate these two | |
663 | constructs, or may leave them distinct, in the expectation that the | |
664 | formatter will nevertheless treat them the same.) | |
665 | ||
666 | =item * | |
667 | ||
668 | When rendering Pod to a format that allows comments (i.e., to nearly | |
669 | any format other than plaintext), a Pod formatter must insert comment | |
670 | text identifying its name and version number, and the name and | |
671 | version numbers of any modules it might be using to process the Pod. | |
672 | Minimal examples: | |
673 | ||
674 | %% POD::Pod2PS v3.14159, using POD::Parser v1.92 | |
210b36aa | 675 | |
8a93676d | 676 | <!-- Pod::HTML v3.14159, using POD::Parser v1.92 --> |
210b36aa | 677 | |
8a93676d | 678 | {\doccomm generated by Pod::Tree::RTF 3.14159 using Pod::Tree 1.08} |
210b36aa | 679 | |
8a93676d SB |
680 | .\" Pod::Man version 3.14159, using POD::Parser version 1.92 |
681 | ||
682 | Formatters may also insert additional comments, including: the | |
683 | release date of the Pod formatter program, the contact address for | |
684 | the author(s) of the formatter, the current time, the name of input | |
685 | file, the formatting options in effect, version of Perl used, etc. | |
686 | ||
687 | Formatters may also choose to note errors/warnings as comments, | |
688 | besides or instead of emitting them otherwise (as in messages to | |
689 | STDERR, or C<die>ing). | |
690 | ||
691 | =item * | |
692 | ||
693 | Pod parsers I<may> emit warnings or error messages ("Unknown E code | |
694 | EE<lt>zslig>!") to STDERR (whether through printing to STDERR, or | |
695 | C<warn>ing/C<carp>ing, or C<die>ing/C<croak>ing), but I<must> allow | |
696 | suppressing all such STDERR output, and instead allow an option for | |
697 | reporting errors/warnings | |
698 | in some other way, whether by triggering a callback, or noting errors | |
699 | in some attribute of the document object, or some similarly unobtrusive | |
700 | mechanism -- or even by appending a "Pod Errors" section to the end of | |
701 | the parsed form of the document. | |
702 | ||
703 | =item * | |
704 | ||
705 | In cases of exceptionally aberrant documents, Pod parsers may abort the | |
706 | parse. Even then, using C<die>ing/C<croak>ing is to be avoided; where | |
707 | possible, the parser library may simply close the input file | |
708 | and add text like "*** Formatting Aborted ***" to the end of the | |
709 | (partial) in-memory document. | |
710 | ||
711 | =item * | |
712 | ||
713 | In paragraphs where formatting codes (like EE<lt>...>, BE<lt>...>) | |
714 | are understood (i.e., I<not> verbatim paragraphs, but I<including> | |
715 | ordinary paragraphs, and command paragraphs that produce renderable | |
716 | text, like "=head1"), literal whitespace should generally be considered | |
717 | "insignificant", in that one literal space has the same meaning as any | |
718 | (nonzero) number of literal spaces, literal newlines, and literal tabs | |
719 | (as long as this produces no blank lines, since those would terminate | |
720 | the paragraph). Pod parsers should compact literal whitespace in each | |
721 | processed paragraph, but may provide an option for overriding this | |
722 | (since some processing tasks do not require it), or may follow | |
723 | additional special rules (for example, specially treating | |
724 | period-space-space or period-newline sequences). | |
725 | ||
726 | =item * | |
727 | ||
728 | Pod parsers should not, by default, try to coerce apostrophe (') and | |
729 | quote (") into smart quotes (little 9's, 66's, 99's, etc), nor try to | |
730 | turn backtick (`) into anything else but a single backtick character | |
353c6505 | 731 | (distinct from an open quote character!), nor "--" into anything but |
8a93676d SB |
732 | two minus signs. They I<must never> do any of those things to text |
733 | in CE<lt>...> formatting codes, and never I<ever> to text in verbatim | |
734 | paragraphs. | |
735 | ||
736 | =item * | |
737 | ||
738 | When rendering Pod to a format that has two kinds of hyphens (-), one | |
3e666715 | 739 | that's a non-breaking hyphen, and another that's a breakable hyphen |
8a93676d SB |
740 | (as in "object-oriented", which can be split across lines as |
741 | "object-", newline, "oriented"), formatters are encouraged to | |
3e666715 | 742 | generally translate "-" to non-breaking hyphen, but may apply |
8a93676d SB |
743 | heuristics to convert some of these to breaking hyphens. |
744 | ||
745 | =item * | |
746 | ||
747 | Pod formatters should make reasonable efforts to keep words of Perl | |
748 | code from being broken across lines. For example, "Foo::Bar" in some | |
749 | formatting systems is seen as eligible for being broken across lines | |
750 | as "Foo::" newline "Bar" or even "Foo::-" newline "Bar". This should | |
751 | be avoided where possible, either by disabling all line-breaking in | |
752 | mid-word, or by wrapping particular words with internal punctuation | |
753 | in "don't break this across lines" codes (which in some formats may | |
754 | not be a single code, but might be a matter of inserting non-breaking | |
755 | zero-width spaces between every pair of characters in a word.) | |
756 | ||
757 | =item * | |
758 | ||
759 | Pod parsers should, by default, expand tabs in verbatim paragraphs as | |
760 | they are processed, before passing them to the formatter or other | |
761 | processor. Parsers may also allow an option for overriding this. | |
762 | ||
763 | =item * | |
764 | ||
765 | Pod parsers should, by default, remove newlines from the end of | |
766 | ordinary and verbatim paragraphs before passing them to the | |
767 | formatter. For example, while the paragraph you're reading now | |
768 | could be considered, in Pod source, to end with (and contain) | |
769 | the newline(s) that end it, it should be processed as ending with | |
770 | (and containing) the period character that ends this sentence. | |
771 | ||
772 | =item * | |
773 | ||
774 | Pod parsers, when reporting errors, should make some effort to report | |
775 | an approximate line number ("Nested EE<lt>>'s in Paragraph #52, near | |
776 | line 633 of Thing/Foo.pm!"), instead of merely noting the paragraph | |
777 | number ("Nested EE<lt>>'s in Paragraph #52 of Thing/Foo.pm!"). Where | |
778 | this is problematic, the paragraph number should at least be | |
779 | accompanied by an excerpt from the paragraph ("Nested EE<lt>>'s in | |
780 | Paragraph #52 of Thing/Foo.pm, which begins 'Read/write accessor for | |
781 | the CE<lt>interest rate> attribute...'"). | |
782 | ||
783 | =item * | |
784 | ||
785 | Pod parsers, when processing a series of verbatim paragraphs one | |
786 | after another, should consider them to be one large verbatim | |
787 | paragraph that happens to contain blank lines. I.e., these two | |
d1be9408 | 788 | lines, which have a blank line between them: |
8a93676d SB |
789 | |
790 | use Foo; | |
791 | ||
792 | print Foo->VERSION | |
793 | ||
794 | should be unified into one paragraph ("\tuse Foo;\n\n\tprint | |
795 | Foo->VERSION") before being passed to the formatter or other | |
796 | processor. Parsers may also allow an option for overriding this. | |
797 | ||
798 | While this might be too cumbersome to implement in event-based Pod | |
799 | parsers, it is straightforward for parsers that return parse trees. | |
800 | ||
801 | =item * | |
802 | ||
803 | Pod formatters, where feasible, are advised to avoid splitting short | |
804 | verbatim paragraphs (under twelve lines, say) across pages. | |
805 | ||
806 | =item * | |
807 | ||
808 | Pod parsers must treat a line with only spaces and/or tabs on it as a | |
809 | "blank line" such as separates paragraphs. (Some older parsers | |
810 | recognized only two adjacent newlines as a "blank line" but would not | |
811 | recognize a newline, a space, and a newline, as a blank line. This | |
812 | is noncompliant behavior.) | |
813 | ||
814 | =item * | |
815 | ||
816 | Authors of Pod formatters/processors should make every effort to | |
817 | avoid writing their own Pod parser. There are already several in | |
818 | CPAN, with a wide range of interface styles -- and one of them, | |
819 | Pod::Parser, comes with modern versions of Perl. | |
820 | ||
821 | =item * | |
822 | ||
823 | Characters in Pod documents may be conveyed either as literals, or by | |
824 | number in EE<lt>n> codes, or by an equivalent mnemonic, as in | |
825 | EE<lt>eacute> which is exactly equivalent to EE<lt>233>. | |
826 | ||
827 | Characters in the range 32-126 refer to those well known US-ASCII | |
828 | characters (also defined there by Unicode, with the same meaning), | |
829 | which all Pod formatters must render faithfully. Characters | |
830 | in the ranges 0-31 and 127-159 should not be used (neither as | |
831 | literals, nor as EE<lt>number> codes), except for the | |
210b36aa | 832 | literal byte-sequences for newline (13, 13 10, or 10), and tab (9). |
8a93676d SB |
833 | |
834 | Characters in the range 160-255 refer to Latin-1 characters (also | |
835 | defined there by Unicode, with the same meaning). Characters above | |
836 | 255 should be understood to refer to Unicode characters. | |
837 | ||
838 | =item * | |
839 | ||
840 | Be warned | |
841 | that some formatters cannot reliably render characters outside 32-126; | |
842 | and many are able to handle 32-126 and 160-255, but nothing above | |
843 | 255. | |
844 | ||
845 | =item * | |
846 | ||
847 | Besides the well-known "EE<lt>lt>" and "EE<lt>gt>" codes for | |
848 | less-than and greater-than, Pod parsers must understand "EE<lt>sol>" | |
849 | for "/" (solidus, slash), and "EE<lt>verbar>" for "|" (vertical bar, | |
850 | pipe). Pod parsers should also understand "EE<lt>lchevron>" and | |
851 | "EE<lt>rchevron>" as legacy codes for characters 171 and 187, i.e., | |
852 | "left-pointing double angle quotation mark" = "left pointing | |
853 | guillemet" and "right-pointing double angle quotation mark" = "right | |
854 | pointing guillemet". (These look like little "<<" and ">>", and they | |
855 | are now preferably expressed with the HTML/XHTML codes "EE<lt>laquo>" | |
856 | and "EE<lt>raquo>".) | |
857 | ||
858 | =item * | |
859 | ||
860 | Pod parsers should understand all "EE<lt>html>" codes as defined | |
861 | in the entity declarations in the most recent XHTML specification at | |
862 | C<www.W3.org>. Pod parsers must understand at least the entities | |
863 | that define characters in the range 160-255 (Latin-1). Pod parsers, | |
864 | when faced with some unknown "EE<lt>I<identifier>>" code, | |
865 | shouldn't simply replace it with nullstring (by default, at least), | |
866 | but may pass it through as a string consisting of the literal characters | |
867 | E, less-than, I<identifier>, greater-than. Or Pod parsers may offer the | |
868 | alternative option of processing such unknown | |
869 | "EE<lt>I<identifier>>" codes by firing an event especially | |
870 | for such codes, or by adding a special node-type to the in-memory | |
871 | document tree. Such "EE<lt>I<identifier>>" may have special meaning | |
872 | to some processors, or some processors may choose to add them to | |
873 | a special error report. | |
874 | ||
875 | =item * | |
876 | ||
877 | Pod parsers must also support the XHTML codes "EE<lt>quot>" for | |
878 | character 34 (doublequote, "), "EE<lt>amp>" for character 38 | |
879 | (ampersand, &), and "EE<lt>apos>" for character 39 (apostrophe, '). | |
880 | ||
881 | =item * | |
882 | ||
883 | Note that in all cases of "EE<lt>whatever>", I<whatever> (whether | |
884 | an htmlname, or a number in any base) must consist only of | |
885 | alphanumeric characters -- that is, I<whatever> must watch | |
886 | C<m/\A\w+\z/>. So "EE<lt> 0 1 2 3 >" is invalid, because | |
887 | it contains spaces, which aren't alphanumeric characters. This | |
888 | presumably does not I<need> special treatment by a Pod processor; | |
889 | " 0 1 2 3 " doesn't look like a number in any base, so it would | |
890 | presumably be looked up in the table of HTML-like names. Since | |
210b36aa | 891 | there isn't (and cannot be) an HTML-like entity called " 0 1 2 3 ", |
8a93676d SB |
892 | this will be treated as an error. However, Pod processors may |
893 | treat "EE<lt> 0 1 2 3 >" or "EE<lt>e-acute>" as I<syntactically> | |
894 | invalid, potentially earning a different error message than the | |
895 | error message (or warning, or event) generated by a merely unknown | |
896 | (but theoretically valid) htmlname, as in "EE<lt>qacute>" | |
897 | [sic]. However, Pod parsers are not required to make this | |
898 | distinction. | |
899 | ||
900 | =item * | |
901 | ||
902 | Note that EE<lt>number> I<must not> be interpreted as simply | |
903 | "codepoint I<number> in the current/native character set". It always | |
904 | means only "the character represented by codepoint I<number> in | |
905 | Unicode." (This is identical to the semantics of &#I<number>; in XML.) | |
906 | ||
907 | This will likely require many formatters to have tables mapping from | |
908 | treatable Unicode codepoints (such as the "\xE9" for the e-acute | |
909 | character) to the escape sequences or codes necessary for conveying | |
910 | such sequences in the target output format. A converter to *roff | |
911 | would, for example know that "\xE9" (whether conveyed literally, or via | |
912 | a EE<lt>...> sequence) is to be conveyed as "e\\*'". | |
8939ba94 | 913 | Similarly, a program rendering Pod in a Mac OS application window, would |
8a93676d | 914 | presumably need to know that "\xE9" maps to codepoint 142 in MacRoman |
8939ba94 | 915 | encoding that (at time of writing) is native for Mac OS. Such |
8a93676d SB |
916 | Unicode2whatever mappings are presumably already widely available for |
917 | common output formats. (Such mappings may be incomplete! Implementers | |
918 | are not expected to bend over backwards in an attempt to render | |
919 | Cherokee syllabics, Etruscan runes, Byzantine musical symbols, or any | |
920 | of the other weird things that Unicode can encode.) And | |
921 | if a Pod document uses a character not found in such a mapping, the | |
922 | formatter should consider it an unrenderable character. | |
923 | ||
924 | =item * | |
925 | ||
926 | If, surprisingly, the implementor of a Pod formatter can't find a | |
927 | satisfactory pre-existing table mapping from Unicode characters to | |
928 | escapes in the target format (e.g., a decent table of Unicode | |
929 | characters to *roff escapes), it will be necessary to build such a | |
930 | table. If you are in this circumstance, you should begin with the | |
931 | characters in the range 0x00A0 - 0x00FF, which is mostly the heavily | |
932 | used accented characters. Then proceed (as patience permits and | |
933 | fastidiousness compels) through the characters that the (X)HTML | |
934 | standards groups judged important enough to merit mnemonics | |
935 | for. These are declared in the (X)HTML specifications at the | |
936 | www.W3.org site. At time of writing (September 2001), the most recent | |
937 | entity declaration files are: | |
938 | ||
939 | http://www.w3.org/TR/xhtml1/DTD/xhtml-lat1.ent | |
940 | http://www.w3.org/TR/xhtml1/DTD/xhtml-special.ent | |
941 | http://www.w3.org/TR/xhtml1/DTD/xhtml-symbol.ent | |
942 | ||
943 | Then you can progress through any remaining notable Unicode characters | |
944 | in the range 0x2000-0x204D (consult the character tables at | |
945 | www.unicode.org), and whatever else strikes your fancy. For example, | |
946 | in F<xhtml-symbol.ent>, there is the entry: | |
947 | ||
948 | <!ENTITY infin "∞"> <!-- infinity, U+221E ISOtech --> | |
949 | ||
950 | While the mapping "infin" to the character "\x{221E}" will (hopefully) | |
951 | have been already handled by the Pod parser, the presence of the | |
952 | character in this file means that it's reasonably important enough to | |
953 | include in a formatter's table that maps from notable Unicode characters | |
954 | to the codes necessary for rendering them. So for a Unicode-to-*roff | |
955 | mapping, for example, this would merit the entry: | |
956 | ||
957 | "\x{221E}" => '\(in', | |
958 | ||
959 | It is eagerly hoped that in the future, increasing numbers of formats | |
960 | (and formatters) will support Unicode characters directly (as (X)HTML | |
961 | does with C<∞>, C<∞>, or C<∞>), reducing the need | |
962 | for idiosyncratic mappings of Unicode-to-I<my_escapes>. | |
963 | ||
964 | =item * | |
965 | ||
353c6505 | 966 | It is up to individual Pod formatter to display good judgement when |
8a93676d SB |
967 | confronted with an unrenderable character (which is distinct from an |
968 | unknown EE<lt>thing> sequence that the parser couldn't resolve to | |
969 | anything, renderable or not). It is good practice to map Latin letters | |
970 | with diacritics (like "EE<lt>eacute>"/"EE<lt>233>") to the corresponding | |
971 | unaccented US-ASCII letters (like a simple character 101, "e"), but | |
210b36aa | 972 | clearly this is often not feasible, and an unrenderable character may |
8a93676d SB |
973 | be represented as "?", or the like. In attempting a sane fallback |
974 | (as from EE<lt>233> to "e"), Pod formatters may use the | |
975 | %Latin1Code_to_fallback table in L<Pod::Escapes|Pod::Escapes>, or | |
976 | L<Text::Unidecode|Text::Unidecode>, if available. | |
977 | ||
978 | For example, this Pod text: | |
979 | ||
980 | magic is enabled if you set C<$Currency> to 'E<euro>'. | |
981 | ||
982 | may be rendered as: | |
983 | "magic is enabled if you set C<$Currency> to 'I<?>'" or as | |
984 | "magic is enabled if you set C<$Currency> to 'B<[euro]>'", or as | |
985 | "magic is enabled if you set C<$Currency> to '[x20AC]', etc. | |
986 | ||
987 | A Pod formatter may also note, in a comment or warning, a list of what | |
988 | unrenderable characters were encountered. | |
989 | ||
990 | =item * | |
991 | ||
992 | EE<lt>...> may freely appear in any formatting code (other than | |
993 | in another EE<lt>...> or in an ZE<lt>>). That is, "XE<lt>The | |
994 | EE<lt>euro>1,000,000 Solution>" is valid, as is "LE<lt>The | |
995 | EE<lt>euro>1,000,000 Solution|Million::Euros>". | |
996 | ||
997 | =item * | |
998 | ||
3e666715 | 999 | Some Pod formatters output to formats that implement non-breaking |
8a93676d | 1000 | spaces as an individual character (which I'll call "NBSP"), and |
3e666715 | 1001 | others output to formats that implement non-breaking spaces just as |
8a93676d SB |
1002 | spaces wrapped in a "don't break this across lines" code. Note that |
1003 | at the level of Pod, both sorts of codes can occur: Pod can contain a | |
1004 | NBSP character (whether as a literal, or as a "EE<lt>160>" or | |
1005 | "EE<lt>nbsp>" code); and Pod can contain "SE<lt>foo | |
1006 | IE<lt>barE<gt> baz>" codes, where "mere spaces" (character 32) in | |
3e666715 | 1007 | such codes are taken to represent non-breaking spaces. Pod |
8a93676d SB |
1008 | parsers should consider supporting the optional parsing of "SE<lt>foo |
1009 | IE<lt>barE<gt> baz>" as if it were | |
1010 | "fooI<NBSP>IE<lt>barE<gt>I<NBSP>baz", and, going the other way, the | |
1011 | optional parsing of groups of words joined by NBSP's as if each group | |
1012 | were in a SE<lt>...> code, so that formatters may use the | |
1013 | representation that maps best to what the output format demands. | |
1014 | ||
1015 | =item * | |
1016 | ||
210b36aa | 1017 | Some processors may find that the C<SE<lt>...E<gt>> code is easiest to |
8a93676d SB |
1018 | implement by replacing each space in the parse tree under the content |
1019 | of the S, with an NBSP. But note: the replacement should apply I<not> to | |
1020 | spaces in I<all> text, but I<only> to spaces in I<printable> text. (This | |
1021 | distinction may or may not be evident in the particular tree/event | |
1022 | model implemented by the Pod parser.) For example, consider this | |
1023 | unusual case: | |
1024 | ||
1025 | S<L</Autoloaded Functions>> | |
1026 | ||
1027 | This means that the space in the middle of the visible link text must | |
1028 | not be broken across lines. In other words, it's the same as this: | |
1029 | ||
1030 | L<"AutoloadedE<160>Functions"/Autoloaded Functions> | |
1031 | ||
1032 | However, a misapplied space-to-NBSP replacement could (wrongly) | |
1033 | produce something equivalent to this: | |
1034 | ||
1035 | L<"AutoloadedE<160>Functions"/AutoloadedE<160>Functions> | |
1036 | ||
1037 | ...which is almost definitely not going to work as a hyperlink (assuming | |
1038 | this formatter outputs a format supporting hypertext). | |
1039 | ||
1040 | Formatters may choose to just not support the S format code, | |
1041 | especially in cases where the output format simply has no NBSP | |
1042 | character/code and no code for "don't break this stuff across lines". | |
1043 | ||
1044 | =item * | |
1045 | ||
1046 | Besides the NBSP character discussed above, implementors are reminded | |
1047 | of the existence of the other "special" character in Latin-1, the | |
210b36aa | 1048 | "soft hyphen" character, also known as "discretionary hyphen", |
8a93676d SB |
1049 | i.e. C<EE<lt>173E<gt>> = C<EE<lt>0xADE<gt>> = |
1050 | C<EE<lt>shyE<gt>>). This character expresses an optional hyphenation | |
1051 | point. That is, it normally renders as nothing, but may render as a | |
1052 | "-" if a formatter breaks the word at that point. Pod formatters | |
1053 | should, as appropriate, do one of the following: 1) render this with | |
1054 | a code with the same meaning (e.g., "\-" in RTF), 2) pass it through | |
1055 | in the expectation that the formatter understands this character as | |
1056 | such, or 3) delete it. | |
1057 | ||
1058 | For example: | |
1059 | ||
1060 | sigE<shy>action | |
1061 | manuE<shy>script | |
1062 | JarkE<shy>ko HieE<shy>taE<shy>nieE<shy>mi | |
1063 | ||
1064 | These signal to a formatter that if it is to hyphenate "sigaction" | |
1065 | or "manuscript", then it should be done as | |
1066 | "sig-I<[linebreak]>action" or "manu-I<[linebreak]>script" | |
1067 | (and if it doesn't hyphenate it, then the C<EE<lt>shyE<gt>> doesn't | |
1068 | show up at all). And if it is | |
1069 | to hyphenate "Jarkko" and/or "Hietaniemi", it can do | |
1070 | so only at the points where there is a C<EE<lt>shyE<gt>> code. | |
1071 | ||
1072 | In practice, it is anticipated that this character will not be used | |
1073 | often, but formatters should either support it, or delete it. | |
1074 | ||
1075 | =item * | |
1076 | ||
1077 | If you think that you want to add a new command to Pod (like, say, a | |
1078 | "=biblio" command), consider whether you could get the same | |
1079 | effect with a for or begin/end sequence: "=for biblio ..." or "=begin | |
1080 | biblio" ... "=end biblio". Pod processors that don't understand | |
1081 | "=for biblio", etc, will simply ignore it, whereas they may complain | |
1082 | loudly if they see "=biblio". | |
1083 | ||
1084 | =item * | |
1085 | ||
1086 | Throughout this document, "Pod" has been the preferred spelling for | |
1087 | the name of the documentation format. One may also use "POD" or | |
da75cd15 | 1088 | "pod". For the documentation that is (typically) in the Pod |
8a93676d SB |
1089 | format, you may use "pod", or "Pod", or "POD". Understanding these |
1090 | distinctions is useful; but obsessing over how to spell them, usually | |
1091 | is not. | |
1092 | ||
1093 | =back | |
1094 | ||
1095 | ||
1096 | ||
1097 | ||
1098 | ||
1099 | =head1 About LE<lt>...E<gt> Codes | |
1100 | ||
1101 | As you can tell from a glance at L<perlpod|perlpod>, the LE<lt>...> | |
1102 | code is the most complex of the Pod formatting codes. The points below | |
1103 | will hopefully clarify what it means and how processors should deal | |
1104 | with it. | |
1105 | ||
1106 | =over | |
1107 | ||
1108 | =item * | |
1109 | ||
1110 | In parsing an LE<lt>...> code, Pod parsers must distinguish at least | |
1111 | four attributes: | |
1112 | ||
1113 | =over | |
1114 | ||
1115 | =item First: | |
1116 | ||
1117 | The link-text. If there is none, this must be undef. (E.g., in | |
1118 | "LE<lt>Perl Functions|perlfunc>", the link-text is "Perl Functions". | |
1119 | In "LE<lt>Time::HiRes>" and even "LE<lt>|Time::HiRes>", there is no | |
1120 | link text. Note that link text may contain formatting.) | |
1121 | ||
1122 | =item Second: | |
1123 | ||
ac036724 | 1124 | The possibly inferred link-text; i.e., if there was no real link |
8a93676d SB |
1125 | text, then this is the text that we'll infer in its place. (E.g., for |
1126 | "LE<lt>Getopt::Std>", the inferred link text is "Getopt::Std".) | |
1127 | ||
1128 | =item Third: | |
1129 | ||
1130 | The name or URL, or undef if none. (E.g., in "LE<lt>Perl | |
ac036724 | 1131 | Functions|perlfunc>", the name (also sometimes called the page) |
8a93676d SB |
1132 | is "perlfunc". In "LE<lt>/CAVEATS>", the name is undef.) |
1133 | ||
1134 | =item Fourth: | |
1135 | ||
1136 | The section (AKA "item" in older perlpods), or undef if none. E.g., | |
f41e638c | 1137 | in "LE<lt>Getopt::Std/DESCRIPTIONE<gt>", "DESCRIPTION" is the section. (Note |
8a93676d SB |
1138 | that this is not the same as a manpage section like the "5" in "man 5 |
1139 | crontab". "Section Foo" in the Pod sense means the part of the text | |
6edf2346 | 1140 | that's introduced by the heading or item whose text is "Foo".) |
8a93676d SB |
1141 | |
1142 | =back | |
1143 | ||
1144 | Pod parsers may also note additional attributes including: | |
1145 | ||
1146 | =over | |
1147 | ||
1148 | =item Fifth: | |
1149 | ||
1150 | A flag for whether item 3 (if present) is a URL (like | |
1151 | "http://lists.perl.org" is), in which case there should be no section | |
1152 | attribute; a Pod name (like "perldoc" and "Getopt::Std" are); or | |
1153 | possibly a man page name (like "crontab(5)" is). | |
1154 | ||
1155 | =item Sixth: | |
1156 | ||
1157 | The raw original LE<lt>...> content, before text is split on | |
1158 | "|", "/", etc, and before EE<lt>...> codes are expanded. | |
1159 | ||
1160 | =back | |
1161 | ||
1162 | (The above were numbered only for concise reference below. It is not | |
1163 | a requirement that these be passed as an actual list or array.) | |
1164 | ||
1165 | For example: | |
1166 | ||
1167 | L<Foo::Bar> | |
1168 | => undef, # link text | |
1169 | "Foo::Bar", # possibly inferred link text | |
1170 | "Foo::Bar", # name | |
1171 | undef, # section | |
1172 | 'pod', # what sort of link | |
1173 | "Foo::Bar" # original content | |
1174 | ||
1175 | L<Perlport's section on NL's|perlport/Newlines> | |
1176 | => "Perlport's section on NL's", # link text | |
1177 | "Perlport's section on NL's", # possibly inferred link text | |
1178 | "perlport", # name | |
1179 | "Newlines", # section | |
1180 | 'pod', # what sort of link | |
1181 | "Perlport's section on NL's|perlport/Newlines" # orig. content | |
1182 | ||
1183 | L<perlport/Newlines> | |
1184 | => undef, # link text | |
1185 | '"Newlines" in perlport', # possibly inferred link text | |
1186 | "perlport", # name | |
1187 | "Newlines", # section | |
1188 | 'pod', # what sort of link | |
1189 | "perlport/Newlines" # original content | |
1190 | ||
1191 | L<crontab(5)/"DESCRIPTION"> | |
1192 | => undef, # link text | |
1193 | '"DESCRIPTION" in crontab(5)', # possibly inferred link text | |
1194 | "crontab(5)", # name | |
1195 | "DESCRIPTION", # section | |
1196 | 'man', # what sort of link | |
1197 | 'crontab(5)/"DESCRIPTION"' # original content | |
1198 | ||
1199 | L</Object Attributes> | |
1200 | => undef, # link text | |
1201 | '"Object Attributes"', # possibly inferred link text | |
1202 | undef, # name | |
1203 | "Object Attributes", # section | |
1204 | 'pod', # what sort of link | |
1205 | "/Object Attributes" # original content | |
1206 | ||
1207 | L<http://www.perl.org/> | |
1208 | => undef, # link text | |
1209 | "http://www.perl.org/", # possibly inferred link text | |
1210 | "http://www.perl.org/", # name | |
1211 | undef, # section | |
1212 | 'url', # what sort of link | |
1213 | "http://www.perl.org/" # original content | |
1214 | ||
f6e963e4 RS |
1215 | L<Perl.org|http://www.perl.org/> |
1216 | => "Perl.org", # link text | |
1217 | "http://www.perl.org/", # possibly inferred link text | |
1218 | "http://www.perl.org/", # name | |
1219 | undef, # section | |
1220 | 'url', # what sort of link | |
1221 | "Perl.org|http://www.perl.org/" # original content | |
1222 | ||
8a93676d SB |
1223 | Note that you can distinguish URL-links from anything else by the |
1224 | fact that they match C<m/\A\w+:[^:\s]\S*\z/>. So | |
1225 | C<LE<lt>http://www.perl.comE<gt>> is a URL, but | |
1226 | C<LE<lt>HTTP::ResponseE<gt>> isn't. | |
1227 | ||
1228 | =item * | |
1229 | ||
1230 | In case of LE<lt>...> codes with no "text|" part in them, | |
1231 | older formatters have exhibited great variation in actually displaying | |
1232 | the link or cross reference. For example, LE<lt>crontab(5)> would render | |
1233 | as "the C<crontab(5)> manpage", or "in the C<crontab(5)> manpage" | |
1234 | or just "C<crontab(5)>". | |
1235 | ||
1236 | Pod processors must now treat "text|"-less links as follows: | |
1237 | ||
1238 | L<name> => L<name|name> | |
1239 | L</section> => L<"section"|/section> | |
1240 | L<name/section> => L<"section" in name|name/section> | |
1241 | ||
1242 | =item * | |
1243 | ||
1244 | Note that section names might contain markup. I.e., if a section | |
1245 | starts with: | |
1246 | ||
1247 | =head2 About the C<-M> Operator | |
1248 | ||
1249 | or with: | |
1250 | ||
1251 | =item About the C<-M> Operator | |
1252 | ||
1253 | then a link to it would look like this: | |
1254 | ||
1255 | L<somedoc/About the C<-M> Operator> | |
1256 | ||
1257 | Formatters may choose to ignore the markup for purposes of resolving | |
1258 | the link and use only the renderable characters in the section name, | |
1259 | as in: | |
1260 | ||
1261 | <h1><a name="About_the_-M_Operator">About the <code>-M</code> | |
1262 | Operator</h1> | |
210b36aa | 1263 | |
8a93676d | 1264 | ... |
210b36aa | 1265 | |
8a93676d SB |
1266 | <a href="somedoc#About_the_-M_Operator">About the <code>-M</code> |
1267 | Operator" in somedoc</a> | |
1268 | ||
1269 | =item * | |
1270 | ||
1271 | Previous versions of perlpod distinguished C<LE<lt>name/"section"E<gt>> | |
1272 | links from C<LE<lt>name/itemE<gt>> links (and their targets). These | |
1273 | have been merged syntactically and semantically in the current | |
1274 | specification, and I<section> can refer either to a "=headI<n> Heading | |
1275 | Content" command or to a "=item Item Content" command. This | |
1276 | specification does not specify what behavior should be in the case | |
1277 | of a given document having several things all seeming to produce the | |
1278 | same I<section> identifier (e.g., in HTML, several things all producing | |
1279 | the same I<anchorname> in <a name="I<anchorname>">...</a> | |
1280 | elements). Where Pod processors can control this behavior, they should | |
1281 | use the first such anchor. That is, C<LE<lt>Foo/BarE<gt>> refers to the | |
1282 | I<first> "Bar" section in Foo. | |
1283 | ||
1284 | But for some processors/formats this cannot be easily controlled; as | |
1285 | with the HTML example, the behavior of multiple ambiguous | |
1286 | <a name="I<anchorname>">...</a> is most easily just left up to | |
1287 | browsers to decide. | |
1288 | ||
1289 | =item * | |
1290 | ||
1291 | Authors wanting to link to a particular (absolute) URL, must do so | |
1292 | only with "LE<lt>scheme:...>" codes (like | |
1293 | LE<lt>http://www.perl.org>), and must not attempt "LE<lt>Some Site | |
1294 | Name|scheme:...>" codes. This restriction avoids many problems | |
1295 | in parsing and rendering LE<lt>...> codes. | |
1296 | ||
1297 | =item * | |
1298 | ||
1299 | In a C<LE<lt>text|...E<gt>> code, text may contain formatting codes | |
1300 | for formatting or for EE<lt>...> escapes, as in: | |
1301 | ||
1302 | L<B<ummE<234>stuff>|...> | |
1303 | ||
1304 | For C<LE<lt>...E<gt>> codes without a "name|" part, only | |
ac036724 | 1305 | C<EE<lt>...E<gt>> and C<ZE<lt>E<gt>> codes may occur. That is, |
1306 | authors should not use "C<LE<lt>BE<lt>Foo::BarE<gt>E<gt>>". | |
8a93676d SB |
1307 | |
1308 | Note, however, that formatting codes and ZE<lt>>'s can occur in any | |
1309 | and all parts of an LE<lt>...> (i.e., in I<name>, I<section>, I<text>, | |
1310 | and I<url>). | |
1311 | ||
1312 | Authors must not nest LE<lt>...> codes. For example, "LE<lt>The | |
1313 | LE<lt>Foo::Bar> man page>" should be treated as an error. | |
1314 | ||
1315 | =item * | |
1316 | ||
1317 | Note that Pod authors may use formatting codes inside the "text" | |
1318 | part of "LE<lt>text|name>" (and so on for LE<lt>text|/"sec">). | |
1319 | ||
1320 | In other words, this is valid: | |
1321 | ||
1322 | Go read L<the docs on C<$.>|perlvar/"$."> | |
1323 | ||
1324 | Some output formats that do allow rendering "LE<lt>...>" codes as | |
1325 | hypertext, might not allow the link-text to be formatted; in | |
1326 | that case, formatters will have to just ignore that formatting. | |
1327 | ||
1328 | =item * | |
1329 | ||
1330 | At time of writing, C<LE<lt>nameE<gt>> values are of two types: | |
1331 | either the name of a Pod page like C<LE<lt>Foo::BarE<gt>> (which | |
1332 | might be a real Perl module or program in an @INC / PATH | |
e1020413 | 1333 | directory, or a .pod file in those places); or the name of a Unix |
8a93676d SB |
1334 | man page, like C<LE<lt>crontab(5)E<gt>>. In theory, C<LE<lt>chmodE<gt>> |
1335 | in ambiguous between a Pod page called "chmod", or the Unix man page | |
1336 | "chmod" (in whatever man-section). However, the presence of a string | |
1337 | in parens, as in "crontab(5)", is sufficient to signal that what | |
1338 | is being discussed is not a Pod page, and so is presumably a | |
e1020413 | 1339 | Unix man page. The distinction is of no importance to many |
8a93676d SB |
1340 | Pod processors, but some processors that render to hypertext formats |
1341 | may need to distinguish them in order to know how to render a | |
1342 | given C<LE<lt>fooE<gt>> code. | |
1343 | ||
1344 | =item * | |
1345 | ||
b41aadf2 RS |
1346 | Previous versions of perlpod allowed for a C<LE<lt>sectionE<gt>> syntax (as in |
1347 | C<LE<lt>Object AttributesE<gt>>), which was not easily distinguishable from | |
1348 | C<LE<lt>nameE<gt>> syntax and for C<LE<lt>"section"E<gt>> which was only | |
1349 | slightly less ambiguous. This syntax is no longer in the specification, and | |
1350 | has been replaced by the C<LE<lt>/sectionE<gt>> syntax (where the slash was | |
1351 | formerly optional). Pod parsers should tolerate the C<LE<lt>"section"E<gt>> | |
1352 | syntax, for a while at least. The suggested heuristic for distinguishing | |
1353 | C<LE<lt>sectionE<gt>> from C<LE<lt>nameE<gt>> is that if it contains any | |
1354 | whitespace, it's a I<section>. Pod processors should warn about this being | |
1355 | deprecated syntax. | |
8a93676d SB |
1356 | |
1357 | =back | |
1358 | ||
1359 | =head1 About =over...=back Regions | |
1360 | ||
1361 | "=over"..."=back" regions are used for various kinds of list-like | |
1362 | structures. (I use the term "region" here simply as a collective | |
1363 | term for everything from the "=over" to the matching "=back".) | |
1364 | ||
1365 | =over | |
1366 | ||
1367 | =item * | |
1368 | ||
1369 | The non-zero numeric I<indentlevel> in "=over I<indentlevel>" ... | |
1370 | "=back" is used for giving the formatter a clue as to how many | |
1371 | "spaces" (ems, or roughly equivalent units) it should tab over, | |
1372 | although many formatters will have to convert this to an absolute | |
1373 | measurement that may not exactly match with the size of spaces (or M's) | |
1374 | in the document's base font. Other formatters may have to completely | |
1375 | ignore the number. The lack of any explicit I<indentlevel> parameter is | |
1376 | equivalent to an I<indentlevel> value of 4. Pod processors may | |
1377 | complain if I<indentlevel> is present but is not a positive number | |
1378 | matching C<m/\A(\d*\.)?\d+\z/>. | |
1379 | ||
1380 | =item * | |
1381 | ||
1382 | Authors of Pod formatters are reminded that "=over" ... "=back" may | |
1383 | map to several different constructs in your output format. For | |
1384 | example, in converting Pod to (X)HTML, it can map to any of | |
1385 | <ul>...</ul>, <ol>...</ol>, <dl>...</dl>, or | |
1386 | <blockquote>...</blockquote>. Similarly, "=item" can map to <li> or | |
1387 | <dt>. | |
1388 | ||
1389 | =item * | |
1390 | ||
1391 | Each "=over" ... "=back" region should be one of the following: | |
1392 | ||
1393 | =over | |
1394 | ||
1395 | =item * | |
1396 | ||
1397 | An "=over" ... "=back" region containing only "=item *" commands, | |
1398 | each followed by some number of ordinary/verbatim paragraphs, other | |
1399 | nested "=over" ... "=back" regions, "=for..." paragraphs, and | |
1400 | "=begin"..."=end" regions. | |
1401 | ||
1402 | (Pod processors must tolerate a bare "=item" as if it were "=item | |
1403 | *".) Whether "*" is rendered as a literal asterisk, an "o", or as | |
1404 | some kind of real bullet character, is left up to the Pod formatter, | |
1405 | and may depend on the level of nesting. | |
1406 | ||
1407 | =item * | |
1408 | ||
1409 | An "=over" ... "=back" region containing only | |
1410 | C<m/\A=item\s+\d+\.?\s*\z/> paragraphs, each one (or each group of them) | |
1411 | followed by some number of ordinary/verbatim paragraphs, other nested | |
1412 | "=over" ... "=back" regions, "=for..." paragraphs, and/or | |
1413 | "=begin"..."=end" codes. Note that the numbers must start at 1 | |
1414 | in each section, and must proceed in order and without skipping | |
1415 | numbers. | |
1416 | ||
1417 | (Pod processors must tolerate lines like "=item 1" as if they were | |
1418 | "=item 1.", with the period.) | |
1419 | ||
1420 | =item * | |
1421 | ||
1422 | An "=over" ... "=back" region containing only "=item [text]" | |
1423 | commands, each one (or each group of them) followed by some number of | |
1424 | ordinary/verbatim paragraphs, other nested "=over" ... "=back" | |
1425 | regions, or "=for..." paragraphs, and "=begin"..."=end" regions. | |
1426 | ||
1427 | The "=item [text]" paragraph should not match | |
1428 | C<m/\A=item\s+\d+\.?\s*\z/> or C<m/\A=item\s+\*\s*\z/>, nor should it | |
1429 | match just C<m/\A=item\s*\z/>. | |
1430 | ||
1431 | =item * | |
1432 | ||
1433 | An "=over" ... "=back" region containing no "=item" paragraphs at | |
1434 | all, and containing only some number of | |
1435 | ordinary/verbatim paragraphs, and possibly also some nested "=over" | |
1436 | ... "=back" regions, "=for..." paragraphs, and "=begin"..."=end" | |
1437 | regions. Such an itemless "=over" ... "=back" region in Pod is | |
1438 | equivalent in meaning to a "<blockquote>...</blockquote>" element in | |
1439 | HTML. | |
1440 | ||
1441 | =back | |
1442 | ||
1443 | Note that with all the above cases, you can determine which type of | |
1444 | "=over" ... "=back" you have, by examining the first (non-"=cut", | |
1445 | non-"=pod") Pod paragraph after the "=over" command. | |
1446 | ||
1447 | =item * | |
1448 | ||
1449 | Pod formatters I<must> tolerate arbitrarily large amounts of text | |
1450 | in the "=item I<text...>" paragraph. In practice, most such | |
1451 | paragraphs are short, as in: | |
1452 | ||
1453 | =item For cutting off our trade with all parts of the world | |
1454 | ||
1455 | But they may be arbitrarily long: | |
1456 | ||
1457 | =item For transporting us beyond seas to be tried for pretended | |
1458 | offenses | |
1459 | ||
1460 | =item He is at this time transporting large armies of foreign | |
1461 | mercenaries to complete the works of death, desolation and | |
1462 | tyranny, already begun with circumstances of cruelty and perfidy | |
1463 | scarcely paralleled in the most barbarous ages, and totally | |
1464 | unworthy the head of a civilized nation. | |
1465 | ||
1466 | =item * | |
1467 | ||
1468 | Pod processors should tolerate "=item *" / "=item I<number>" commands | |
1469 | with no accompanying paragraph. The middle item is an example: | |
1470 | ||
1471 | =over | |
210b36aa | 1472 | |
8a93676d | 1473 | =item 1 |
210b36aa | 1474 | |
8a93676d | 1475 | Pick up dry cleaning. |
210b36aa | 1476 | |
8a93676d | 1477 | =item 2 |
210b36aa | 1478 | |
8a93676d | 1479 | =item 3 |
210b36aa | 1480 | |
8a93676d | 1481 | Stop by the store. Get Abba Zabas, Stoli, and cheap lawn chairs. |
210b36aa | 1482 | |
8a93676d SB |
1483 | =back |
1484 | ||
1485 | =item * | |
1486 | ||
1487 | No "=over" ... "=back" region can contain headings. Processors may | |
1488 | treat such a heading as an error. | |
1489 | ||
1490 | =item * | |
1491 | ||
1492 | Note that an "=over" ... "=back" region should have some | |
1493 | content. That is, authors should not have an empty region like this: | |
1494 | ||
1495 | =over | |
210b36aa | 1496 | |
8a93676d SB |
1497 | =back |
1498 | ||
1499 | Pod processors seeing such a contentless "=over" ... "=back" region, | |
1500 | may ignore it, or may report it as an error. | |
1501 | ||
1502 | =item * | |
1503 | ||
1504 | Processors must tolerate an "=over" list that goes off the end of the | |
1505 | document (i.e., which has no matching "=back"), but they may warn | |
1506 | about such a list. | |
1507 | ||
1508 | =item * | |
1509 | ||
1510 | Authors of Pod formatters should note that this construct: | |
1511 | ||
1512 | =item Neque | |
1513 | ||
1514 | =item Porro | |
1515 | ||
1516 | =item Quisquam Est | |
210b36aa | 1517 | |
8a93676d SB |
1518 | Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci |
1519 | velit, sed quia non numquam eius modi tempora incidunt ut | |
1520 | labore et dolore magnam aliquam quaerat voluptatem. | |
1521 | ||
1522 | =item Ut Enim | |
1523 | ||
1524 | is semantically ambiguous, in a way that makes formatting decisions | |
1525 | a bit difficult. On the one hand, it could be mention of an item | |
1526 | "Neque", mention of another item "Porro", and mention of another | |
1527 | item "Quisquam Est", with just the last one requiring the explanatory | |
1528 | paragraph "Qui dolorem ipsum quia dolor..."; and then an item | |
1529 | "Ut Enim". In that case, you'd want to format it like so: | |
1530 | ||
1531 | Neque | |
210b36aa | 1532 | |
8a93676d | 1533 | Porro |
210b36aa | 1534 | |
8a93676d SB |
1535 | Quisquam Est |
1536 | Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci | |
1537 | velit, sed quia non numquam eius modi tempora incidunt ut | |
1538 | labore et dolore magnam aliquam quaerat voluptatem. | |
1539 | ||
1540 | Ut Enim | |
1541 | ||
1542 | But it could equally well be a discussion of three (related or equivalent) | |
1543 | items, "Neque", "Porro", and "Quisquam Est", followed by a paragraph | |
1544 | explaining them all, and then a new item "Ut Enim". In that case, you'd | |
1545 | probably want to format it like so: | |
1546 | ||
1547 | Neque | |
1548 | Porro | |
1549 | Quisquam Est | |
1550 | Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci | |
1551 | velit, sed quia non numquam eius modi tempora incidunt ut | |
1552 | labore et dolore magnam aliquam quaerat voluptatem. | |
1553 | ||
1554 | Ut Enim | |
1555 | ||
353c6505 | 1556 | But (for the foreseeable future), Pod does not provide any way for Pod |
8a93676d SB |
1557 | authors to distinguish which grouping is meant by the above |
1558 | "=item"-cluster structure. So formatters should format it like so: | |
1559 | ||
1560 | Neque | |
1561 | ||
1562 | Porro | |
1563 | ||
1564 | Quisquam Est | |
1565 | ||
1566 | Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci | |
1567 | velit, sed quia non numquam eius modi tempora incidunt ut | |
1568 | labore et dolore magnam aliquam quaerat voluptatem. | |
1569 | ||
1570 | Ut Enim | |
1571 | ||
210b36aa | 1572 | That is, there should be (at least roughly) equal spacing between |
8a93676d SB |
1573 | items as between paragraphs (although that spacing may well be less |
1574 | than the full height of a line of text). This leaves it to the reader | |
1575 | to use (con)textual cues to figure out whether the "Qui dolorem | |
1576 | ipsum..." paragraph applies to the "Quisquam Est" item or to all three | |
1577 | items "Neque", "Porro", and "Quisquam Est". While not an ideal | |
1578 | situation, this is preferable to providing formatting cues that may | |
1579 | be actually contrary to the author's intent. | |
1580 | ||
1581 | =back | |
1582 | ||
1583 | ||
1584 | ||
1585 | =head1 About Data Paragraphs and "=begin/=end" Regions | |
1586 | ||
1587 | Data paragraphs are typically used for inlining non-Pod data that is | |
1588 | to be used (typically passed through) when rendering the document to | |
1589 | a specific format: | |
1590 | ||
1591 | =begin rtf | |
210b36aa | 1592 | |
8a93676d | 1593 | \par{\pard\qr\sa4500{\i Printed\~\chdate\~\chtime}\par} |
210b36aa | 1594 | |
8a93676d SB |
1595 | =end rtf |
1596 | ||
1597 | The exact same effect could, incidentally, be achieved with a single | |
1598 | "=for" paragraph: | |
1599 | ||
1600 | =for rtf \par{\pard\qr\sa4500{\i Printed\~\chdate\~\chtime}\par} | |
1601 | ||
1602 | (Although that is not formally a data paragraph, it has the same | |
1603 | meaning as one, and Pod parsers may parse it as one.) | |
1604 | ||
1605 | Another example of a data paragraph: | |
1606 | ||
1607 | =begin html | |
210b36aa | 1608 | |
8a93676d | 1609 | I like <em>PIE</em>! |
210b36aa | 1610 | |
8a93676d | 1611 | <hr>Especially pecan pie! |
210b36aa | 1612 | |
8a93676d SB |
1613 | =end html |
1614 | ||
1615 | If these were ordinary paragraphs, the Pod parser would try to | |
1616 | expand the "EE<lt>/em>" (in the first paragraph) as a formatting | |
1617 | code, just like "EE<lt>lt>" or "EE<lt>eacute>". But since this | |
1618 | is in a "=begin I<identifier>"..."=end I<identifier>" region I<and> | |
1619 | the identifier "html" doesn't begin have a ":" prefix, the contents | |
1620 | of this region are stored as data paragraphs, instead of being | |
1621 | processed as ordinary paragraphs (or if they began with a spaces | |
1622 | and/or tabs, as verbatim paragraphs). | |
1623 | ||
1624 | As a further example: At time of writing, no "biblio" identifier is | |
1625 | supported, but suppose some processor were written to recognize it as | |
1626 | a way of (say) denoting a bibliographic reference (necessarily | |
1627 | containing formatting codes in ordinary paragraphs). The fact that | |
1628 | "biblio" paragraphs were meant for ordinary processing would be | |
1629 | indicated by prefacing each "biblio" identifier with a colon: | |
1630 | ||
1631 | =begin :biblio | |
1632 | ||
1633 | Wirth, Niklaus. 1976. I<Algorithms + Data Structures = | |
1634 | Programs.> Prentice-Hall, Englewood Cliffs, NJ. | |
1635 | ||
1636 | =end :biblio | |
1637 | ||
1638 | This would signal to the parser that paragraphs in this begin...end | |
1639 | region are subject to normal handling as ordinary/verbatim paragraphs | |
1640 | (while still tagged as meant only for processors that understand the | |
1641 | "biblio" identifier). The same effect could be had with: | |
1642 | ||
1643 | =for :biblio | |
1644 | Wirth, Niklaus. 1976. I<Algorithms + Data Structures = | |
1645 | Programs.> Prentice-Hall, Englewood Cliffs, NJ. | |
1646 | ||
1647 | The ":" on these identifiers means simply "process this stuff | |
1648 | normally, even though the result will be for some special target". | |
1649 | I suggest that parser APIs report "biblio" as the target identifier, | |
1650 | but also report that it had a ":" prefix. (And similarly, with the | |
1651 | above "html", report "html" as the target identifier, and note the | |
1652 | I<lack> of a ":" prefix.) | |
1653 | ||
1654 | Note that a "=begin I<identifier>"..."=end I<identifier>" region where | |
1655 | I<identifier> begins with a colon, I<can> contain commands. For example: | |
1656 | ||
1657 | =begin :biblio | |
210b36aa | 1658 | |
8a93676d | 1659 | Wirth's classic is available in several editions, including: |
210b36aa | 1660 | |
8a93676d SB |
1661 | =for comment |
1662 | hm, check abebooks.com for how much used copies cost. | |
210b36aa | 1663 | |
8a93676d | 1664 | =over |
210b36aa | 1665 | |
8a93676d | 1666 | =item |
210b36aa | 1667 | |
8a93676d SB |
1668 | Wirth, Niklaus. 1975. I<Algorithmen und Datenstrukturen.> |
1669 | Teubner, Stuttgart. [Yes, it's in German.] | |
210b36aa | 1670 | |
8a93676d | 1671 | =item |
210b36aa | 1672 | |
8a93676d SB |
1673 | Wirth, Niklaus. 1976. I<Algorithms + Data Structures = |
1674 | Programs.> Prentice-Hall, Englewood Cliffs, NJ. | |
210b36aa | 1675 | |
8a93676d | 1676 | =back |
210b36aa | 1677 | |
8a93676d SB |
1678 | =end :biblio |
1679 | ||
1680 | Note, however, a "=begin I<identifier>"..."=end I<identifier>" | |
1681 | region where I<identifier> does I<not> begin with a colon, should not | |
1682 | directly contain "=head1" ... "=head4" commands, nor "=over", nor "=back", | |
1683 | nor "=item". For example, this may be considered invalid: | |
1684 | ||
1685 | =begin somedata | |
210b36aa | 1686 | |
8a93676d | 1687 | This is a data paragraph. |
210b36aa | 1688 | |
8a93676d | 1689 | =head1 Don't do this! |
210b36aa | 1690 | |
8a93676d | 1691 | This is a data paragraph too. |
210b36aa | 1692 | |
8a93676d SB |
1693 | =end somedata |
1694 | ||
1695 | A Pod processor may signal that the above (specifically the "=head1" | |
1696 | paragraph) is an error. Note, however, that the following should | |
1697 | I<not> be treated as an error: | |
1698 | ||
1699 | =begin somedata | |
210b36aa | 1700 | |
8a93676d | 1701 | This is a data paragraph. |
210b36aa | 1702 | |
8a93676d | 1703 | =cut |
210b36aa | 1704 | |
8a93676d SB |
1705 | # Yup, this isn't Pod anymore. |
1706 | sub excl { (rand() > .5) ? "hoo!" : "hah!" } | |
210b36aa | 1707 | |
8a93676d | 1708 | =pod |
210b36aa | 1709 | |
8a93676d | 1710 | This is a data paragraph too. |
210b36aa | 1711 | |
8a93676d SB |
1712 | =end somedata |
1713 | ||
1714 | And this too is valid: | |
1715 | ||
1716 | =begin someformat | |
210b36aa | 1717 | |
8a93676d | 1718 | This is a data paragraph. |
210b36aa | 1719 | |
8a93676d | 1720 | And this is a data paragraph. |
210b36aa | 1721 | |
8a93676d | 1722 | =begin someotherformat |
210b36aa | 1723 | |
8a93676d | 1724 | This is a data paragraph too. |
210b36aa | 1725 | |
8a93676d | 1726 | And this is a data paragraph too. |
210b36aa | 1727 | |
8a93676d SB |
1728 | =begin :yetanotherformat |
1729 | ||
1730 | =head2 This is a command paragraph! | |
1731 | ||
1732 | This is an ordinary paragraph! | |
210b36aa | 1733 | |
8a93676d | 1734 | And this is a verbatim paragraph! |
210b36aa | 1735 | |
8a93676d | 1736 | =end :yetanotherformat |
210b36aa | 1737 | |
8a93676d | 1738 | =end someotherformat |
210b36aa | 1739 | |
8a93676d | 1740 | Another data paragraph! |
210b36aa | 1741 | |
8a93676d SB |
1742 | =end someformat |
1743 | ||
1744 | The contents of the above "=begin :yetanotherformat" ... | |
1745 | "=end :yetanotherformat" region I<aren't> data paragraphs, because | |
1746 | the immediately containing region's identifier (":yetanotherformat") | |
1747 | begins with a colon. In practice, most regions that contain | |
1748 | data paragraphs will contain I<only> data paragraphs; however, | |
1749 | the above nesting is syntactically valid as Pod, even if it is | |
1750 | rare. However, the handlers for some formats, like "html", | |
1751 | will accept only data paragraphs, not nested regions; and they may | |
1752 | complain if they see (targeted for them) nested regions, or commands, | |
1753 | other than "=end", "=pod", and "=cut". | |
1754 | ||
1755 | Also consider this valid structure: | |
1756 | ||
1757 | =begin :biblio | |
210b36aa | 1758 | |
8a93676d | 1759 | Wirth's classic is available in several editions, including: |
210b36aa | 1760 | |
8a93676d | 1761 | =over |
210b36aa | 1762 | |
8a93676d | 1763 | =item |
210b36aa | 1764 | |
8a93676d SB |
1765 | Wirth, Niklaus. 1975. I<Algorithmen und Datenstrukturen.> |
1766 | Teubner, Stuttgart. [Yes, it's in German.] | |
210b36aa | 1767 | |
8a93676d | 1768 | =item |
210b36aa | 1769 | |
8a93676d SB |
1770 | Wirth, Niklaus. 1976. I<Algorithms + Data Structures = |
1771 | Programs.> Prentice-Hall, Englewood Cliffs, NJ. | |
1772 | ||
1773 | =back | |
210b36aa | 1774 | |
8a93676d | 1775 | Buy buy buy! |
210b36aa | 1776 | |
8a93676d | 1777 | =begin html |
210b36aa | 1778 | |
8a93676d | 1779 | <img src='wirth_spokesmodeling_book.png'> |
210b36aa | 1780 | |
8a93676d | 1781 | <hr> |
210b36aa | 1782 | |
8a93676d | 1783 | =end html |
210b36aa | 1784 | |
8a93676d | 1785 | Now now now! |
210b36aa | 1786 | |
8a93676d SB |
1787 | =end :biblio |
1788 | ||
1789 | There, the "=begin html"..."=end html" region is nested inside | |
1790 | the larger "=begin :biblio"..."=end :biblio" region. Note that the | |
1791 | content of the "=begin html"..."=end html" region is data | |
1792 | paragraph(s), because the immediately containing region's identifier | |
1793 | ("html") I<doesn't> begin with a colon. | |
1794 | ||
1795 | Pod parsers, when processing a series of data paragraphs one | |
1796 | after another (within a single region), should consider them to | |
1797 | be one large data paragraph that happens to contain blank lines. So | |
1798 | the content of the above "=begin html"..."=end html" I<may> be stored | |
1799 | as two data paragraphs (one consisting of | |
1800 | "<img src='wirth_spokesmodeling_book.png'>\n" | |
1801 | and another consisting of "<hr>\n"), but I<should> be stored as | |
1802 | a single data paragraph (consisting of | |
1803 | "<img src='wirth_spokesmodeling_book.png'>\n\n<hr>\n"). | |
1804 | ||
1805 | Pod processors should tolerate empty | |
1806 | "=begin I<something>"..."=end I<something>" regions, | |
1807 | empty "=begin :I<something>"..."=end :I<something>" regions, and | |
1808 | contentless "=for I<something>" and "=for :I<something>" | |
1809 | paragraphs. I.e., these should be tolerated: | |
1810 | ||
1811 | =for html | |
210b36aa | 1812 | |
8a93676d | 1813 | =begin html |
210b36aa | 1814 | |
8a93676d | 1815 | =end html |
210b36aa | 1816 | |
8a93676d | 1817 | =begin :biblio |
210b36aa | 1818 | |
8a93676d SB |
1819 | =end :biblio |
1820 | ||
1821 | Incidentally, note that there's no easy way to express a data | |
1822 | paragraph starting with something that looks like a command. Consider: | |
1823 | ||
1824 | =begin stuff | |
210b36aa | 1825 | |
8a93676d | 1826 | =shazbot |
210b36aa | 1827 | |
8a93676d SB |
1828 | =end stuff |
1829 | ||
1830 | There, "=shazbot" will be parsed as a Pod command "shazbot", not as a data | |
1831 | paragraph "=shazbot\n". However, you can express a data paragraph consisting | |
1832 | of "=shazbot\n" using this code: | |
1833 | ||
1834 | =for stuff =shazbot | |
1835 | ||
1836 | The situation where this is necessary, is presumably quite rare. | |
1837 | ||
1838 | Note that =end commands must match the currently open =begin command. That | |
1839 | is, they must properly nest. For example, this is valid: | |
1840 | ||
1841 | =begin outer | |
210b36aa | 1842 | |
8a93676d | 1843 | X |
210b36aa | 1844 | |
8a93676d | 1845 | =begin inner |
210b36aa | 1846 | |
8a93676d | 1847 | Y |
210b36aa | 1848 | |
8a93676d | 1849 | =end inner |
210b36aa | 1850 | |
8a93676d | 1851 | Z |
210b36aa | 1852 | |
8a93676d SB |
1853 | =end outer |
1854 | ||
1855 | while this is invalid: | |
1856 | ||
1857 | =begin outer | |
210b36aa | 1858 | |
8a93676d | 1859 | X |
210b36aa | 1860 | |
8a93676d | 1861 | =begin inner |
210b36aa | 1862 | |
8a93676d | 1863 | Y |
210b36aa | 1864 | |
8a93676d | 1865 | =end outer |
210b36aa | 1866 | |
8a93676d | 1867 | Z |
210b36aa | 1868 | |
8a93676d | 1869 | =end inner |
210b36aa | 1870 | |
8a93676d SB |
1871 | This latter is improper because when the "=end outer" command is seen, the |
1872 | currently open region has the formatname "inner", not "outer". (It just | |
1873 | happens that "outer" is the format name of a higher-up region.) This is | |
1874 | an error. Processors must by default report this as an error, and may halt | |
210b36aa | 1875 | processing the document containing that error. A corollary of this is that |
ac036724 | 1876 | regions cannot "overlap". That is, the latter block above does not represent |
8a93676d SB |
1877 | a region called "outer" which contains X and Y, overlapping a region called |
1878 | "inner" which contains Y and Z. But because it is invalid (as all | |
1879 | apparently overlapping regions would be), it doesn't represent that, or | |
1880 | anything at all. | |
1881 | ||
1882 | Similarly, this is invalid: | |
1883 | ||
1884 | =begin thing | |
210b36aa | 1885 | |
8a93676d SB |
1886 | =end hting |
1887 | ||
1888 | This is an error because the region is opened by "thing", and the "=end" | |
1889 | tries to close "hting" [sic]. | |
1890 | ||
1891 | This is also invalid: | |
1892 | ||
1893 | =begin thing | |
210b36aa | 1894 | |
8a93676d SB |
1895 | =end |
1896 | ||
1897 | This is invalid because every "=end" command must have a formatname | |
1898 | parameter. | |
1899 | ||
1900 | =head1 SEE ALSO | |
1901 | ||
1902 | L<perlpod>, L<perlsyn/"PODs: Embedded Documentation">, | |
1903 | L<podchecker> | |
1904 | ||
1905 | =head1 AUTHOR | |
1906 | ||
1907 | Sean M. Burke | |
1908 | ||
1909 | =cut | |
1910 | ||
1911 |