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1 | =encoding utf8 |
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2 | |
3 | =head1 NAME |
4 | |
5 | perlpodspec - Plain Old Documentation: format specification and notes |
6 | |
7 | =head1 DESCRIPTION |
8 | |
9 | This document is detailed notes on the Pod markup language. Most |
10 | people will only have to read L<perlpod|perlpod> to know how to write |
11 | in Pod, but this document may answer some incidental questions to do |
12 | with parsing and rendering Pod. |
13 | |
14 | In this document, "must" / "must not", "should" / |
15 | "should not", and "may" have their conventional (cf. RFC 2119) |
16 | meanings: "X must do Y" means that if X doesn't do Y, it's against |
17 | this specification, and should really be fixed. "X should do Y" |
18 | means that it's recommended, but X may fail to do Y, if there's a |
19 | good reason. "X may do Y" is merely a note that X can do Y at |
20 | will (although it is up to the reader to detect any connotation of |
21 | "and I think it would be I<nice> if X did Y" versus "it wouldn't |
22 | really I<bother> me if X did Y"). |
23 | |
24 | Notably, when I say "the parser should do Y", the |
25 | parser may fail to do Y, if the calling application explicitly |
26 | requests that the parser I<not> do Y. I often phrase this as |
27 | "the parser should, by default, do Y." This doesn't I<require> |
28 | the parser to provide an option for turning off whatever |
29 | feature Y is (like expanding tabs in verbatim paragraphs), although |
30 | it implicates that such an option I<may> be provided. |
31 | |
32 | =head1 Pod Definitions |
33 | |
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34 | Pod is embedded in files, typically Perl source files, although you |
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35 | can write a file that's nothing but Pod. |
36 | |
37 | A B<line> in a file consists of zero or more non-newline characters, |
38 | terminated by either a newline or the end of the file. |
39 | |
40 | A B<newline sequence> is usually a platform-dependent concept, but |
41 | Pod parsers should understand it to mean any of CR (ASCII 13), LF |
42 | (ASCII 10), or a CRLF (ASCII 13 followed immediately by ASCII 10), in |
43 | addition to any other system-specific meaning. The first CR/CRLF/LF |
44 | sequence in the file may be used as the basis for identifying the |
45 | newline sequence for parsing the rest of the file. |
46 | |
47 | A B<blank line> is a line consisting entirely of zero or more spaces |
48 | (ASCII 32) or tabs (ASCII 9), and terminated by a newline or end-of-file. |
49 | A B<non-blank line> is a line containing one or more characters other |
50 | than space or tab (and terminated by a newline or end-of-file). |
51 | |
52 | (I<Note:> Many older Pod parsers did not accept a line consisting of |
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53 | spaces/tabs and then a newline as a blank line. The only lines they |
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54 | considered blank were lines consisting of I<no characters at all>, |
55 | terminated by a newline.) |
56 | |
57 | B<Whitespace> is used in this document as a blanket term for spaces, |
58 | tabs, and newline sequences. (By itself, this term usually refers |
59 | to literal whitespace. That is, sequences of whitespace characters |
60 | in Pod source, as opposed to "EE<lt>32>", which is a formatting |
61 | code that I<denotes> a whitespace character.) |
62 | |
63 | A B<Pod parser> is a module meant for parsing Pod (regardless of |
64 | whether this involves calling callbacks or building a parse tree or |
65 | directly formatting it). A B<Pod formatter> (or B<Pod translator>) |
66 | is a module or program that converts Pod to some other format (HTML, |
67 | plaintext, TeX, PostScript, RTF). A B<Pod processor> might be a |
68 | formatter or translator, or might be a program that does something |
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69 | else with the Pod (like counting words, scanning for index points, |
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70 | etc.). |
71 | |
72 | Pod content is contained in B<Pod blocks>. A Pod block starts with a |
73 | line that matches <m/\A=[a-zA-Z]/>, and continues up to the next line |
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74 | that matches C<m/\A=cut/> or up to the end of the file if there is |
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75 | no C<m/\A=cut/> line. |
76 | |
77 | =for comment |
78 | The current perlsyn says: |
79 | [beginquote] |
80 | Note that pod translators should look at only paragraphs beginning |
81 | with a pod directive (it makes parsing easier), whereas the compiler |
82 | actually knows to look for pod escapes even in the middle of a |
83 | paragraph. This means that the following secret stuff will be ignored |
84 | by both the compiler and the translators. |
85 | $a=3; |
86 | =secret stuff |
87 | warn "Neither POD nor CODE!?" |
88 | =cut back |
89 | print "got $a\n"; |
90 | You probably shouldn't rely upon the warn() being podded out forever. |
91 | Not all pod translators are well-behaved in this regard, and perhaps |
92 | the compiler will become pickier. |
93 | [endquote] |
94 | I think that those paragraphs should just be removed; paragraph-based |
95 | parsing seems to have been largely abandoned, because of the hassle |
96 | with non-empty blank lines messing up what people meant by "paragraph". |
97 | Even if the "it makes parsing easier" bit were especially true, |
98 | it wouldn't be worth the confusion of having perl and pod2whatever |
99 | actually disagree on what can constitute a Pod block. |
100 | |
101 | Within a Pod block, there are B<Pod paragraphs>. A Pod paragraph |
102 | consists of non-blank lines of text, separated by one or more blank |
103 | lines. |
104 | |
105 | For purposes of Pod processing, there are four types of paragraphs in |
106 | a Pod block: |
107 | |
108 | =over |
109 | |
110 | =item * |
111 | |
112 | A command paragraph (also called a "directive"). The first line of |
113 | this paragraph must match C<m/\A=[a-zA-Z]/>. Command paragraphs are |
114 | typically one line, as in: |
115 | |
116 | =head1 NOTES |
117 | |
118 | =item * |
119 | |
120 | But they may span several (non-blank) lines: |
121 | |
122 | =for comment |
123 | Hm, I wonder what it would look like if |
124 | you tried to write a BNF for Pod from this. |
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125 | |
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126 | =head3 Dr. Strangelove, or: How I Learned to |
127 | Stop Worrying and Love the Bomb |
128 | |
129 | I<Some> command paragraphs allow formatting codes in their content |
130 | (i.e., after the part that matches C<m/\A=[a-zA-Z]\S*\s*/>), as in: |
131 | |
132 | =head1 Did You Remember to C<use strict;>? |
133 | |
134 | In other words, the Pod processing handler for "head1" will apply the |
135 | same processing to "Did You Remember to CE<lt>use strict;>?" that it |
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136 | would to an ordinary paragraph (i.e., formatting codes like |
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137 | "CE<lt>...>") are parsed and presumably formatted appropriately, and |
138 | whitespace in the form of literal spaces and/or tabs is not |
139 | significant. |
140 | |
141 | =item * |
142 | |
143 | A B<verbatim paragraph>. The first line of this paragraph must be a |
144 | literal space or tab, and this paragraph must not be inside a "=begin |
145 | I<identifier>", ... "=end I<identifier>" sequence unless |
146 | "I<identifier>" begins with a colon (":"). That is, if a paragraph |
147 | starts with a literal space or tab, but I<is> inside a |
148 | "=begin I<identifier>", ... "=end I<identifier>" region, then it's |
149 | a data paragraph, unless "I<identifier>" begins with a colon. |
150 | |
151 | Whitespace I<is> significant in verbatim paragraphs (although, in |
152 | processing, tabs are probably expanded). |
153 | |
154 | =item * |
155 | |
156 | An B<ordinary paragraph>. A paragraph is an ordinary paragraph |
157 | if its first line matches neither C<m/\A=[a-zA-Z]/> nor |
158 | C<m/\A[ \t]/>, I<and> if it's not inside a "=begin I<identifier>", |
159 | ... "=end I<identifier>" sequence unless "I<identifier>" begins with |
160 | a colon (":"). |
161 | |
162 | =item * |
163 | |
164 | A B<data paragraph>. This is a paragraph that I<is> inside a "=begin |
165 | I<identifier>" ... "=end I<identifier>" sequence where |
166 | "I<identifier>" does I<not> begin with a literal colon (":"). In |
167 | some sense, a data paragraph is not part of Pod at all (i.e., |
168 | effectively it's "out-of-band"), since it's not subject to most kinds |
169 | of Pod parsing; but it is specified here, since Pod |
170 | parsers need to be able to call an event for it, or store it in some |
171 | form in a parse tree, or at least just parse I<around> it. |
172 | |
173 | =back |
174 | |
175 | For example: consider the following paragraphs: |
176 | |
177 | # <- that's the 0th column |
178 | |
179 | =head1 Foo |
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180 | |
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181 | Stuff |
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182 | |
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183 | $foo->bar |
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184 | |
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185 | =cut |
186 | |
187 | Here, "=head1 Foo" and "=cut" are command paragraphs because the first |
188 | line of each matches C<m/\A=[a-zA-Z]/>. "I<[space][space]>$foo->bar" |
189 | is a verbatim paragraph, because its first line starts with a literal |
190 | whitespace character (and there's no "=begin"..."=end" region around). |
191 | |
192 | The "=begin I<identifier>" ... "=end I<identifier>" commands stop |
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193 | paragraphs that they surround from being parsed as ordinary or verbatim |
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194 | paragraphs, if I<identifier> doesn't begin with a colon. This |
195 | is discussed in detail in the section |
196 | L</About Data Paragraphs and "=beginE<sol>=end" Regions>. |
197 | |
198 | =head1 Pod Commands |
199 | |
200 | This section is intended to supplement and clarify the discussion in |
201 | L<perlpod/"Command Paragraph">. These are the currently recognized |
202 | Pod commands: |
203 | |
204 | =over |
205 | |
206 | =item "=head1", "=head2", "=head3", "=head4" |
207 | |
208 | This command indicates that the text in the remainder of the paragraph |
209 | is a heading. That text may contain formatting codes. Examples: |
210 | |
211 | =head1 Object Attributes |
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212 | |
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213 | =head3 What B<Not> to Do! |
214 | |
215 | =item "=pod" |
216 | |
217 | This command indicates that this paragraph begins a Pod block. (If we |
218 | are already in the middle of a Pod block, this command has no effect at |
219 | all.) If there is any text in this command paragraph after "=pod", |
220 | it must be ignored. Examples: |
221 | |
222 | =pod |
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223 | |
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224 | This is a plain Pod paragraph. |
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225 | |
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226 | =pod This text is ignored. |
227 | |
228 | =item "=cut" |
229 | |
230 | This command indicates that this line is the end of this previously |
231 | started Pod block. If there is any text after "=cut" on the line, it must be |
232 | ignored. Examples: |
233 | |
234 | =cut |
235 | |
236 | =cut The documentation ends here. |
237 | |
238 | =cut |
239 | # This is the first line of program text. |
240 | sub foo { # This is the second. |
241 | |
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242 | It is an error to try to I<start> a Pod block with a "=cut" command. In |
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243 | that case, the Pod processor must halt parsing of the input file, and |
244 | must by default emit a warning. |
245 | |
246 | =item "=over" |
247 | |
248 | This command indicates that this is the start of a list/indent |
249 | region. If there is any text following the "=over", it must consist |
250 | of only a nonzero positive numeral. The semantics of this numeral is |
251 | explained in the L</"About =over...=back Regions"> section, further |
252 | below. Formatting codes are not expanded. Examples: |
253 | |
254 | =over 3 |
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255 | |
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256 | =over 3.5 |
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257 | |
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258 | =over |
259 | |
260 | =item "=item" |
261 | |
262 | This command indicates that an item in a list begins here. Formatting |
263 | codes are processed. The semantics of the (optional) text in the |
264 | remainder of this paragraph are |
265 | explained in the L</"About =over...=back Regions"> section, further |
266 | below. Examples: |
267 | |
268 | =item |
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269 | |
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270 | =item * |
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271 | |
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272 | =item * |
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273 | |
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274 | =item 14 |
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275 | |
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276 | =item 3. |
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277 | |
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278 | =item C<< $thing->stuff(I<dodad>) >> |
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279 | |
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280 | =item For transporting us beyond seas to be tried for pretended |
281 | offenses |
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282 | |
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283 | =item He is at this time transporting large armies of foreign |
284 | mercenaries to complete the works of death, desolation and |
285 | tyranny, already begun with circumstances of cruelty and perfidy |
286 | scarcely paralleled in the most barbarous ages, and totally |
287 | unworthy the head of a civilized nation. |
288 | |
289 | =item "=back" |
290 | |
291 | This command indicates that this is the end of the region begun |
292 | by the most recent "=over" command. It permits no text after the |
293 | "=back" command. |
294 | |
295 | =item "=begin formatname" |
296 | |
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297 | =item "=begin formatname parameter" |
298 | |
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299 | This marks the following paragraphs (until the matching "=end |
300 | formatname") as being for some special kind of processing. Unless |
301 | "formatname" begins with a colon, the contained non-command |
302 | paragraphs are data paragraphs. But if "formatname" I<does> begin |
303 | with a colon, then non-command paragraphs are ordinary paragraphs |
304 | or data paragraphs. This is discussed in detail in the section |
305 | L</About Data Paragraphs and "=beginE<sol>=end" Regions>. |
306 | |
307 | It is advised that formatnames match the regexp |
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308 | C<m/\A:?[−a−zA−Z0−9_]+\z/>. Everything following whitespace after the |
309 | formatname is a parameter that may be used by the formatter when dealing |
310 | with this region. This parameter must not be repeated in the "=end" |
311 | paragraph. Implementors should anticipate future expansion in the |
312 | semantics and syntax of the first parameter to "=begin"/"=end"/"=for". |
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313 | |
314 | =item "=end formatname" |
315 | |
316 | This marks the end of the region opened by the matching |
317 | "=begin formatname" region. If "formatname" is not the formatname |
318 | of the most recent open "=begin formatname" region, then this |
319 | is an error, and must generate an error message. This |
320 | is discussed in detail in the section |
321 | L</About Data Paragraphs and "=beginE<sol>=end" Regions>. |
322 | |
323 | =item "=for formatname text..." |
324 | |
325 | This is synonymous with: |
326 | |
327 | =begin formatname |
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328 | |
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329 | text... |
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330 | |
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331 | =end formatname |
332 | |
333 | That is, it creates a region consisting of a single paragraph; that |
334 | paragraph is to be treated as a normal paragraph if "formatname" |
335 | begins with a ":"; if "formatname" I<doesn't> begin with a colon, |
336 | then "text..." will constitute a data paragraph. There is no way |
337 | to use "=for formatname text..." to express "text..." as a verbatim |
338 | paragraph. |
339 | |
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340 | =item "=encoding encodingname" |
341 | |
342 | This command, which should occur early in the document (at least |
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343 | before any non-US-ASCII data!), declares that this document is |
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344 | encoded in the encoding I<encodingname>, which must be |
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345 | an encoding name that L<Encode> recognizes. (Encode's list |
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346 | of supported encodings, in L<Encode::Supported>, is useful here.) |
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347 | If the Pod parser cannot decode the declared encoding, it |
348 | should emit a warning and may abort parsing the document |
349 | altogether. |
350 | |
351 | A document having more than one "=encoding" line should be |
352 | considered an error. Pod processors may silently tolerate this if |
353 | the not-first "=encoding" lines are just duplicates of the |
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354 | first one (e.g., if there's a "=encoding utf8" line, and later on |
355 | another "=encoding utf8" line). But Pod processors should complain if |
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356 | there are contradictory "=encoding" lines in the same document |
357 | (e.g., if there is a "=encoding utf8" early in the document and |
358 | "=encoding big5" later). Pod processors that recognize BOMs |
359 | may also complain if they see an "=encoding" line |
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360 | that contradicts the BOM (e.g., if a document with a UTF-16LE |
361 | BOM has an "=encoding shiftjis" line). |
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362 | |
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363 | =back |
364 | |
365 | If a Pod processor sees any command other than the ones listed |
366 | above (like "=head", or "=haed1", or "=stuff", or "=cuttlefish", |
367 | or "=w123"), that processor must by default treat this as an |
368 | error. It must not process the paragraph beginning with that |
369 | command, must by default warn of this as an error, and may |
370 | abort the parse. A Pod parser may allow a way for particular |
371 | applications to add to the above list of known commands, and to |
372 | stipulate, for each additional command, whether formatting |
373 | codes should be processed. |
374 | |
375 | Future versions of this specification may add additional |
376 | commands. |
377 | |
378 | |
379 | |
380 | =head1 Pod Formatting Codes |
381 | |
382 | (Note that in previous drafts of this document and of perlpod, |
383 | formatting codes were referred to as "interior sequences", and |
384 | this term may still be found in the documentation for Pod parsers, |
385 | and in error messages from Pod processors.) |
386 | |
387 | There are two syntaxes for formatting codes: |
388 | |
389 | =over |
390 | |
391 | =item * |
392 | |
393 | A formatting code starts with a capital letter (just US-ASCII [A-Z]) |
394 | followed by a "<", any number of characters, and ending with the first |
395 | matching ">". Examples: |
396 | |
397 | That's what I<you> think! |
398 | |
399 | What's C<dump()> for? |
400 | |
401 | X<C<chmod> and C<unlink()> Under Different Operating Systems> |
402 | |
403 | =item * |
404 | |
405 | A formatting code starts with a capital letter (just US-ASCII [A-Z]) |
406 | followed by two or more "<"'s, one or more whitespace characters, |
407 | any number of characters, one or more whitespace characters, |
408 | and ending with the first matching sequence of two or more ">"'s, where |
409 | the number of ">"'s equals the number of "<"'s in the opening of this |
410 | formatting code. Examples: |
411 | |
412 | That's what I<< you >> think! |
413 | |
414 | C<<< open(X, ">>thing.dat") || die $! >>> |
415 | |
416 | B<< $foo->bar(); >> |
417 | |
418 | With this syntax, the whitespace character(s) after the "CE<lt><<" |
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419 | and before the ">>" (or whatever letter) are I<not> renderable. They |
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420 | do not signify whitespace, are merely part of the formatting codes |
421 | themselves. That is, these are all synonymous: |
422 | |
423 | C<thing> |
424 | C<< thing >> |
425 | C<< thing >> |
426 | C<<< thing >>> |
427 | C<<<< |
428 | thing |
429 | >>>> |
430 | |
431 | and so on. |
432 | |
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433 | Finally, the multiple-angle-bracket form does I<not> alter the interpretation |
434 | of nested formatting codes, meaning that the following four example lines are |
435 | identical in meaning: |
436 | |
437 | B<example: C<$a E<lt>=E<gt> $b>> |
438 | |
439 | B<example: C<< $a <=> $b >>> |
440 | |
441 | B<example: C<< $a E<lt>=E<gt> $b >>> |
442 | |
443 | B<<< example: C<< $a E<lt>=E<gt> $b >> >>> |
444 | |
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445 | =back |
446 | |
447 | In parsing Pod, a notably tricky part is the correct parsing of |
448 | (potentially nested!) formatting codes. Implementors should |
449 | consult the code in the C<parse_text> routine in Pod::Parser as an |
450 | example of a correct implementation. |
451 | |
452 | =over |
453 | |
454 | =item C<IE<lt>textE<gt>> -- italic text |
455 | |
456 | See the brief discussion in L<perlpod/"Formatting Codes">. |
457 | |
458 | =item C<BE<lt>textE<gt>> -- bold text |
459 | |
460 | See the brief discussion in L<perlpod/"Formatting Codes">. |
461 | |
462 | =item C<CE<lt>codeE<gt>> -- code text |
463 | |
464 | See the brief discussion in L<perlpod/"Formatting Codes">. |
465 | |
466 | =item C<FE<lt>filenameE<gt>> -- style for filenames |
467 | |
468 | See the brief discussion in L<perlpod/"Formatting Codes">. |
469 | |
470 | =item C<XE<lt>topic nameE<gt>> -- an index entry |
471 | |
472 | See the brief discussion in L<perlpod/"Formatting Codes">. |
473 | |
474 | This code is unusual in that most formatters completely discard |
475 | this code and its content. Other formatters will render it with |
476 | invisible codes that can be used in building an index of |
477 | the current document. |
478 | |
479 | =item C<ZE<lt>E<gt>> -- a null (zero-effect) formatting code |
480 | |
481 | Discussed briefly in L<perlpod/"Formatting Codes">. |
482 | |
483 | This code is unusual is that it should have no content. That is, |
484 | a processor may complain if it sees C<ZE<lt>potatoesE<gt>>. Whether |
485 | or not it complains, the I<potatoes> text should ignored. |
486 | |
487 | =item C<LE<lt>nameE<gt>> -- a hyperlink |
488 | |
489 | The complicated syntaxes of this code are discussed at length in |
490 | L<perlpod/"Formatting Codes">, and implementation details are |
491 | discussed below, in L</"About LE<lt>...E<gt> Codes">. Parsing the |
492 | contents of LE<lt>content> is tricky. Notably, the content has to be |
493 | checked for whether it looks like a URL, or whether it has to be split |
494 | on literal "|" and/or "/" (in the right order!), and so on, |
495 | I<before> EE<lt>...> codes are resolved. |
496 | |
497 | =item C<EE<lt>escapeE<gt>> -- a character escape |
498 | |
499 | See L<perlpod/"Formatting Codes">, and several points in |
500 | L</Notes on Implementing Pod Processors>. |
501 | |
502 | =item C<SE<lt>textE<gt>> -- text contains non-breaking spaces |
503 | |
504 | This formatting code is syntactically simple, but semantically |
505 | complex. What it means is that each space in the printable |
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506 | content of this code signifies a non-breaking space. |
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507 | |
508 | Consider: |
509 | |
510 | C<$x ? $y : $z> |
511 | |
512 | S<C<$x ? $y : $z>> |
513 | |
514 | Both signify the monospace (c[ode] style) text consisting of |
515 | "$x", one space, "?", one space, ":", one space, "$z". The |
516 | difference is that in the latter, with the S code, those spaces |
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517 | are not "normal" spaces, but instead are non-breaking spaces. |
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518 | |
519 | =back |
520 | |
521 | |
522 | If a Pod processor sees any formatting code other than the ones |
523 | listed above (as in "NE<lt>...>", or "QE<lt>...>", etc.), that |
524 | processor must by default treat this as an error. |
525 | A Pod parser may allow a way for particular |
526 | applications to add to the above list of known formatting codes; |
527 | a Pod parser might even allow a way to stipulate, for each additional |
528 | command, whether it requires some form of special processing, as |
529 | LE<lt>...> does. |
530 | |
531 | Future versions of this specification may add additional |
532 | formatting codes. |
533 | |
534 | Historical note: A few older Pod processors would not see a ">" as |
535 | closing a "CE<lt>" code, if the ">" was immediately preceded by |
536 | a "-". This was so that this: |
537 | |
538 | C<$foo->bar> |
539 | |
540 | would parse as equivalent to this: |
541 | |
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542 | C<$foo-E<gt>bar> |
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543 | |
544 | instead of as equivalent to a "C" formatting code containing |
545 | only "$foo-", and then a "bar>" outside the "C" formatting code. This |
546 | problem has since been solved by the addition of syntaxes like this: |
547 | |
548 | C<< $foo->bar >> |
549 | |
550 | Compliant parsers must not treat "->" as special. |
551 | |
552 | Formatting codes absolutely cannot span paragraphs. If a code is |
553 | opened in one paragraph, and no closing code is found by the end of |
554 | that paragraph, the Pod parser must close that formatting code, |
555 | and should complain (as in "Unterminated I code in the paragraph |
556 | starting at line 123: 'Time objects are not...'"). So these |
557 | two paragraphs: |
558 | |
559 | I<I told you not to do this! |
210b36aa |
560 | |
8a93676d |
561 | Don't make me say it again!> |
562 | |
563 | ...must I<not> be parsed as two paragraphs in italics (with the I |
564 | code starting in one paragraph and starting in another.) Instead, |
565 | the first paragraph should generate a warning, but that aside, the |
566 | above code must parse as if it were: |
567 | |
568 | I<I told you not to do this!> |
210b36aa |
569 | |
8a93676d |
570 | Don't make me say it again!E<gt> |
571 | |
572 | (In SGMLish jargon, all Pod commands are like block-level |
573 | elements, whereas all Pod formatting codes are like inline-level |
574 | elements.) |
575 | |
576 | |
577 | |
578 | =head1 Notes on Implementing Pod Processors |
579 | |
580 | The following is a long section of miscellaneous requirements |
581 | and suggestions to do with Pod processing. |
582 | |
583 | =over |
584 | |
585 | =item * |
586 | |
587 | Pod formatters should tolerate lines in verbatim blocks that are of |
588 | any length, even if that means having to break them (possibly several |
589 | times, for very long lines) to avoid text running off the side of the |
590 | page. Pod formatters may warn of such line-breaking. Such warnings |
591 | are particularly appropriate for lines are over 100 characters long, which |
592 | are usually not intentional. |
593 | |
594 | =item * |
595 | |
596 | Pod parsers must recognize I<all> of the three well-known newline |
597 | formats: CR, LF, and CRLF. See L<perlport|perlport>. |
598 | |
599 | =item * |
600 | |
601 | Pod parsers should accept input lines that are of any length. |
602 | |
603 | =item * |
604 | |
605 | Since Perl recognizes a Unicode Byte Order Mark at the start of files |
606 | as signaling that the file is Unicode encoded as in UTF-16 (whether |
607 | big-endian or little-endian) or UTF-8, Pod parsers should do the |
608 | same. Otherwise, the character encoding should be understood as |
609 | being UTF-8 if the first highbit byte sequence in the file seems |
610 | valid as a UTF-8 sequence, or otherwise as Latin-1. |
611 | |
612 | Future versions of this specification may specify |
613 | how Pod can accept other encodings. Presumably treatment of other |
614 | encodings in Pod parsing would be as in XML parsing: whatever the |
615 | encoding declared by a particular Pod file, content is to be |
616 | stored in memory as Unicode characters. |
617 | |
618 | =item * |
619 | |
620 | The well known Unicode Byte Order Marks are as follows: if the |
621 | file begins with the two literal byte values 0xFE 0xFF, this is |
622 | the BOM for big-endian UTF-16. If the file begins with the two |
623 | literal byte value 0xFF 0xFE, this is the BOM for little-endian |
624 | UTF-16. If the file begins with the three literal byte values |
625 | 0xEF 0xBB 0xBF, this is the BOM for UTF-8. |
626 | |
627 | =for comment |
628 | use bytes; print map sprintf(" 0x%02X", ord $_), split '', "\x{feff}"; |
629 | 0xEF 0xBB 0xBF |
630 | |
631 | =for comment |
1e54db1a |
632 | If toke.c is modified to support UTF-32, add mention of those here. |
8a93676d |
633 | |
634 | =item * |
635 | |
636 | A naive but sufficient heuristic for testing the first highbit |
637 | byte-sequence in a BOM-less file (whether in code or in Pod!), to see |
638 | whether that sequence is valid as UTF-8 (RFC 2279) is to check whether |
639 | that the first byte in the sequence is in the range 0xC0 - 0xFD |
640 | I<and> whether the next byte is in the range |
641 | 0x80 - 0xBF. If so, the parser may conclude that this file is in |
642 | UTF-8, and all highbit sequences in the file should be assumed to |
643 | be UTF-8. Otherwise the parser should treat the file as being |
644 | in Latin-1. In the unlikely circumstance that the first highbit |
645 | sequence in a truly non-UTF-8 file happens to appear to be UTF-8, one |
646 | can cater to our heuristic (as well as any more intelligent heuristic) |
647 | by prefacing that line with a comment line containing a highbit |
648 | sequence that is clearly I<not> valid as UTF-8. A line consisting |
649 | of simply "#", an e-acute, and any non-highbit byte, |
650 | is sufficient to establish this file's encoding. |
651 | |
652 | =for comment |
653 | If/WHEN some brave soul makes these heuristics into a generic |
fae2c0fb |
654 | text-file class (or PerlIO layer?), we can presumably delete |
8a93676d |
655 | mention of these icky details from this file, and can instead |
fae2c0fb |
656 | tell people to just use appropriate class/layer. |
8a93676d |
657 | Auto-recognition of newline sequences would be another desirable |
fae2c0fb |
658 | feature of such a class/layer. |
8a93676d |
659 | HINT HINT HINT. |
660 | |
661 | =for comment |
662 | "The probability that a string of characters |
663 | in any other encoding appears as valid UTF-8 is low" - RFC2279 |
664 | |
665 | =item * |
666 | |
667 | This document's requirements and suggestions about encodings |
668 | do not apply to Pod processors running on non-ASCII platforms, |
669 | notably EBCDIC platforms. |
670 | |
671 | =item * |
672 | |
673 | Pod processors must treat a "=for [label] [content...]" paragraph as |
674 | meaning the same thing as a "=begin [label]" paragraph, content, and |
675 | an "=end [label]" paragraph. (The parser may conflate these two |
676 | constructs, or may leave them distinct, in the expectation that the |
677 | formatter will nevertheless treat them the same.) |
678 | |
679 | =item * |
680 | |
681 | When rendering Pod to a format that allows comments (i.e., to nearly |
682 | any format other than plaintext), a Pod formatter must insert comment |
683 | text identifying its name and version number, and the name and |
684 | version numbers of any modules it might be using to process the Pod. |
685 | Minimal examples: |
686 | |
687 | %% POD::Pod2PS v3.14159, using POD::Parser v1.92 |
210b36aa |
688 | |
8a93676d |
689 | <!-- Pod::HTML v3.14159, using POD::Parser v1.92 --> |
210b36aa |
690 | |
8a93676d |
691 | {\doccomm generated by Pod::Tree::RTF 3.14159 using Pod::Tree 1.08} |
210b36aa |
692 | |
8a93676d |
693 | .\" Pod::Man version 3.14159, using POD::Parser version 1.92 |
694 | |
695 | Formatters may also insert additional comments, including: the |
696 | release date of the Pod formatter program, the contact address for |
697 | the author(s) of the formatter, the current time, the name of input |
698 | file, the formatting options in effect, version of Perl used, etc. |
699 | |
700 | Formatters may also choose to note errors/warnings as comments, |
701 | besides or instead of emitting them otherwise (as in messages to |
702 | STDERR, or C<die>ing). |
703 | |
704 | =item * |
705 | |
706 | Pod parsers I<may> emit warnings or error messages ("Unknown E code |
707 | EE<lt>zslig>!") to STDERR (whether through printing to STDERR, or |
708 | C<warn>ing/C<carp>ing, or C<die>ing/C<croak>ing), but I<must> allow |
709 | suppressing all such STDERR output, and instead allow an option for |
710 | reporting errors/warnings |
711 | in some other way, whether by triggering a callback, or noting errors |
712 | in some attribute of the document object, or some similarly unobtrusive |
713 | mechanism -- or even by appending a "Pod Errors" section to the end of |
714 | the parsed form of the document. |
715 | |
716 | =item * |
717 | |
718 | In cases of exceptionally aberrant documents, Pod parsers may abort the |
719 | parse. Even then, using C<die>ing/C<croak>ing is to be avoided; where |
720 | possible, the parser library may simply close the input file |
721 | and add text like "*** Formatting Aborted ***" to the end of the |
722 | (partial) in-memory document. |
723 | |
724 | =item * |
725 | |
726 | In paragraphs where formatting codes (like EE<lt>...>, BE<lt>...>) |
727 | are understood (i.e., I<not> verbatim paragraphs, but I<including> |
728 | ordinary paragraphs, and command paragraphs that produce renderable |
729 | text, like "=head1"), literal whitespace should generally be considered |
730 | "insignificant", in that one literal space has the same meaning as any |
731 | (nonzero) number of literal spaces, literal newlines, and literal tabs |
732 | (as long as this produces no blank lines, since those would terminate |
733 | the paragraph). Pod parsers should compact literal whitespace in each |
734 | processed paragraph, but may provide an option for overriding this |
735 | (since some processing tasks do not require it), or may follow |
736 | additional special rules (for example, specially treating |
737 | period-space-space or period-newline sequences). |
738 | |
739 | =item * |
740 | |
741 | Pod parsers should not, by default, try to coerce apostrophe (') and |
742 | quote (") into smart quotes (little 9's, 66's, 99's, etc), nor try to |
743 | turn backtick (`) into anything else but a single backtick character |
353c6505 |
744 | (distinct from an open quote character!), nor "--" into anything but |
8a93676d |
745 | two minus signs. They I<must never> do any of those things to text |
746 | in CE<lt>...> formatting codes, and never I<ever> to text in verbatim |
747 | paragraphs. |
748 | |
749 | =item * |
750 | |
751 | When rendering Pod to a format that has two kinds of hyphens (-), one |
3e666715 |
752 | that's a non-breaking hyphen, and another that's a breakable hyphen |
8a93676d |
753 | (as in "object-oriented", which can be split across lines as |
754 | "object-", newline, "oriented"), formatters are encouraged to |
3e666715 |
755 | generally translate "-" to non-breaking hyphen, but may apply |
8a93676d |
756 | heuristics to convert some of these to breaking hyphens. |
757 | |
758 | =item * |
759 | |
760 | Pod formatters should make reasonable efforts to keep words of Perl |
761 | code from being broken across lines. For example, "Foo::Bar" in some |
762 | formatting systems is seen as eligible for being broken across lines |
763 | as "Foo::" newline "Bar" or even "Foo::-" newline "Bar". This should |
764 | be avoided where possible, either by disabling all line-breaking in |
765 | mid-word, or by wrapping particular words with internal punctuation |
766 | in "don't break this across lines" codes (which in some formats may |
767 | not be a single code, but might be a matter of inserting non-breaking |
768 | zero-width spaces between every pair of characters in a word.) |
769 | |
770 | =item * |
771 | |
772 | Pod parsers should, by default, expand tabs in verbatim paragraphs as |
773 | they are processed, before passing them to the formatter or other |
774 | processor. Parsers may also allow an option for overriding this. |
775 | |
776 | =item * |
777 | |
778 | Pod parsers should, by default, remove newlines from the end of |
779 | ordinary and verbatim paragraphs before passing them to the |
780 | formatter. For example, while the paragraph you're reading now |
781 | could be considered, in Pod source, to end with (and contain) |
782 | the newline(s) that end it, it should be processed as ending with |
783 | (and containing) the period character that ends this sentence. |
784 | |
785 | =item * |
786 | |
787 | Pod parsers, when reporting errors, should make some effort to report |
788 | an approximate line number ("Nested EE<lt>>'s in Paragraph #52, near |
789 | line 633 of Thing/Foo.pm!"), instead of merely noting the paragraph |
790 | number ("Nested EE<lt>>'s in Paragraph #52 of Thing/Foo.pm!"). Where |
791 | this is problematic, the paragraph number should at least be |
792 | accompanied by an excerpt from the paragraph ("Nested EE<lt>>'s in |
793 | Paragraph #52 of Thing/Foo.pm, which begins 'Read/write accessor for |
794 | the CE<lt>interest rate> attribute...'"). |
795 | |
796 | =item * |
797 | |
798 | Pod parsers, when processing a series of verbatim paragraphs one |
799 | after another, should consider them to be one large verbatim |
800 | paragraph that happens to contain blank lines. I.e., these two |
d1be9408 |
801 | lines, which have a blank line between them: |
8a93676d |
802 | |
803 | use Foo; |
804 | |
805 | print Foo->VERSION |
806 | |
807 | should be unified into one paragraph ("\tuse Foo;\n\n\tprint |
808 | Foo->VERSION") before being passed to the formatter or other |
809 | processor. Parsers may also allow an option for overriding this. |
810 | |
811 | While this might be too cumbersome to implement in event-based Pod |
812 | parsers, it is straightforward for parsers that return parse trees. |
813 | |
814 | =item * |
815 | |
816 | Pod formatters, where feasible, are advised to avoid splitting short |
817 | verbatim paragraphs (under twelve lines, say) across pages. |
818 | |
819 | =item * |
820 | |
821 | Pod parsers must treat a line with only spaces and/or tabs on it as a |
822 | "blank line" such as separates paragraphs. (Some older parsers |
823 | recognized only two adjacent newlines as a "blank line" but would not |
824 | recognize a newline, a space, and a newline, as a blank line. This |
825 | is noncompliant behavior.) |
826 | |
827 | =item * |
828 | |
829 | Authors of Pod formatters/processors should make every effort to |
830 | avoid writing their own Pod parser. There are already several in |
831 | CPAN, with a wide range of interface styles -- and one of them, |
832 | Pod::Parser, comes with modern versions of Perl. |
833 | |
834 | =item * |
835 | |
836 | Characters in Pod documents may be conveyed either as literals, or by |
837 | number in EE<lt>n> codes, or by an equivalent mnemonic, as in |
838 | EE<lt>eacute> which is exactly equivalent to EE<lt>233>. |
839 | |
840 | Characters in the range 32-126 refer to those well known US-ASCII |
841 | characters (also defined there by Unicode, with the same meaning), |
842 | which all Pod formatters must render faithfully. Characters |
843 | in the ranges 0-31 and 127-159 should not be used (neither as |
844 | literals, nor as EE<lt>number> codes), except for the |
210b36aa |
845 | literal byte-sequences for newline (13, 13 10, or 10), and tab (9). |
8a93676d |
846 | |
847 | Characters in the range 160-255 refer to Latin-1 characters (also |
848 | defined there by Unicode, with the same meaning). Characters above |
849 | 255 should be understood to refer to Unicode characters. |
850 | |
851 | =item * |
852 | |
853 | Be warned |
854 | that some formatters cannot reliably render characters outside 32-126; |
855 | and many are able to handle 32-126 and 160-255, but nothing above |
856 | 255. |
857 | |
858 | =item * |
859 | |
860 | Besides the well-known "EE<lt>lt>" and "EE<lt>gt>" codes for |
861 | less-than and greater-than, Pod parsers must understand "EE<lt>sol>" |
862 | for "/" (solidus, slash), and "EE<lt>verbar>" for "|" (vertical bar, |
863 | pipe). Pod parsers should also understand "EE<lt>lchevron>" and |
864 | "EE<lt>rchevron>" as legacy codes for characters 171 and 187, i.e., |
865 | "left-pointing double angle quotation mark" = "left pointing |
866 | guillemet" and "right-pointing double angle quotation mark" = "right |
867 | pointing guillemet". (These look like little "<<" and ">>", and they |
868 | are now preferably expressed with the HTML/XHTML codes "EE<lt>laquo>" |
869 | and "EE<lt>raquo>".) |
870 | |
871 | =item * |
872 | |
873 | Pod parsers should understand all "EE<lt>html>" codes as defined |
874 | in the entity declarations in the most recent XHTML specification at |
875 | C<www.W3.org>. Pod parsers must understand at least the entities |
876 | that define characters in the range 160-255 (Latin-1). Pod parsers, |
877 | when faced with some unknown "EE<lt>I<identifier>>" code, |
878 | shouldn't simply replace it with nullstring (by default, at least), |
879 | but may pass it through as a string consisting of the literal characters |
880 | E, less-than, I<identifier>, greater-than. Or Pod parsers may offer the |
881 | alternative option of processing such unknown |
882 | "EE<lt>I<identifier>>" codes by firing an event especially |
883 | for such codes, or by adding a special node-type to the in-memory |
884 | document tree. Such "EE<lt>I<identifier>>" may have special meaning |
885 | to some processors, or some processors may choose to add them to |
886 | a special error report. |
887 | |
888 | =item * |
889 | |
890 | Pod parsers must also support the XHTML codes "EE<lt>quot>" for |
891 | character 34 (doublequote, "), "EE<lt>amp>" for character 38 |
892 | (ampersand, &), and "EE<lt>apos>" for character 39 (apostrophe, '). |
893 | |
894 | =item * |
895 | |
896 | Note that in all cases of "EE<lt>whatever>", I<whatever> (whether |
897 | an htmlname, or a number in any base) must consist only of |
898 | alphanumeric characters -- that is, I<whatever> must watch |
899 | C<m/\A\w+\z/>. So "EE<lt> 0 1 2 3 >" is invalid, because |
900 | it contains spaces, which aren't alphanumeric characters. This |
901 | presumably does not I<need> special treatment by a Pod processor; |
902 | " 0 1 2 3 " doesn't look like a number in any base, so it would |
903 | presumably be looked up in the table of HTML-like names. Since |
210b36aa |
904 | there isn't (and cannot be) an HTML-like entity called " 0 1 2 3 ", |
8a93676d |
905 | this will be treated as an error. However, Pod processors may |
906 | treat "EE<lt> 0 1 2 3 >" or "EE<lt>e-acute>" as I<syntactically> |
907 | invalid, potentially earning a different error message than the |
908 | error message (or warning, or event) generated by a merely unknown |
909 | (but theoretically valid) htmlname, as in "EE<lt>qacute>" |
910 | [sic]. However, Pod parsers are not required to make this |
911 | distinction. |
912 | |
913 | =item * |
914 | |
915 | Note that EE<lt>number> I<must not> be interpreted as simply |
916 | "codepoint I<number> in the current/native character set". It always |
917 | means only "the character represented by codepoint I<number> in |
918 | Unicode." (This is identical to the semantics of &#I<number>; in XML.) |
919 | |
920 | This will likely require many formatters to have tables mapping from |
921 | treatable Unicode codepoints (such as the "\xE9" for the e-acute |
922 | character) to the escape sequences or codes necessary for conveying |
923 | such sequences in the target output format. A converter to *roff |
924 | would, for example know that "\xE9" (whether conveyed literally, or via |
925 | a EE<lt>...> sequence) is to be conveyed as "e\\*'". |
8939ba94 |
926 | Similarly, a program rendering Pod in a Mac OS application window, would |
8a93676d |
927 | presumably need to know that "\xE9" maps to codepoint 142 in MacRoman |
8939ba94 |
928 | encoding that (at time of writing) is native for Mac OS. Such |
8a93676d |
929 | Unicode2whatever mappings are presumably already widely available for |
930 | common output formats. (Such mappings may be incomplete! Implementers |
931 | are not expected to bend over backwards in an attempt to render |
932 | Cherokee syllabics, Etruscan runes, Byzantine musical symbols, or any |
933 | of the other weird things that Unicode can encode.) And |
934 | if a Pod document uses a character not found in such a mapping, the |
935 | formatter should consider it an unrenderable character. |
936 | |
937 | =item * |
938 | |
939 | If, surprisingly, the implementor of a Pod formatter can't find a |
940 | satisfactory pre-existing table mapping from Unicode characters to |
941 | escapes in the target format (e.g., a decent table of Unicode |
942 | characters to *roff escapes), it will be necessary to build such a |
943 | table. If you are in this circumstance, you should begin with the |
944 | characters in the range 0x00A0 - 0x00FF, which is mostly the heavily |
945 | used accented characters. Then proceed (as patience permits and |
946 | fastidiousness compels) through the characters that the (X)HTML |
947 | standards groups judged important enough to merit mnemonics |
948 | for. These are declared in the (X)HTML specifications at the |
949 | www.W3.org site. At time of writing (September 2001), the most recent |
950 | entity declaration files are: |
951 | |
952 | http://www.w3.org/TR/xhtml1/DTD/xhtml-lat1.ent |
953 | http://www.w3.org/TR/xhtml1/DTD/xhtml-special.ent |
954 | http://www.w3.org/TR/xhtml1/DTD/xhtml-symbol.ent |
955 | |
956 | Then you can progress through any remaining notable Unicode characters |
957 | in the range 0x2000-0x204D (consult the character tables at |
958 | www.unicode.org), and whatever else strikes your fancy. For example, |
959 | in F<xhtml-symbol.ent>, there is the entry: |
960 | |
961 | <!ENTITY infin "∞"> <!-- infinity, U+221E ISOtech --> |
962 | |
963 | While the mapping "infin" to the character "\x{221E}" will (hopefully) |
964 | have been already handled by the Pod parser, the presence of the |
965 | character in this file means that it's reasonably important enough to |
966 | include in a formatter's table that maps from notable Unicode characters |
967 | to the codes necessary for rendering them. So for a Unicode-to-*roff |
968 | mapping, for example, this would merit the entry: |
969 | |
970 | "\x{221E}" => '\(in', |
971 | |
972 | It is eagerly hoped that in the future, increasing numbers of formats |
973 | (and formatters) will support Unicode characters directly (as (X)HTML |
974 | does with C<∞>, C<∞>, or C<∞>), reducing the need |
975 | for idiosyncratic mappings of Unicode-to-I<my_escapes>. |
976 | |
977 | =item * |
978 | |
353c6505 |
979 | It is up to individual Pod formatter to display good judgement when |
8a93676d |
980 | confronted with an unrenderable character (which is distinct from an |
981 | unknown EE<lt>thing> sequence that the parser couldn't resolve to |
982 | anything, renderable or not). It is good practice to map Latin letters |
983 | with diacritics (like "EE<lt>eacute>"/"EE<lt>233>") to the corresponding |
984 | unaccented US-ASCII letters (like a simple character 101, "e"), but |
210b36aa |
985 | clearly this is often not feasible, and an unrenderable character may |
8a93676d |
986 | be represented as "?", or the like. In attempting a sane fallback |
987 | (as from EE<lt>233> to "e"), Pod formatters may use the |
988 | %Latin1Code_to_fallback table in L<Pod::Escapes|Pod::Escapes>, or |
989 | L<Text::Unidecode|Text::Unidecode>, if available. |
990 | |
991 | For example, this Pod text: |
992 | |
993 | magic is enabled if you set C<$Currency> to 'E<euro>'. |
994 | |
995 | may be rendered as: |
996 | "magic is enabled if you set C<$Currency> to 'I<?>'" or as |
997 | "magic is enabled if you set C<$Currency> to 'B<[euro]>'", or as |
998 | "magic is enabled if you set C<$Currency> to '[x20AC]', etc. |
999 | |
1000 | A Pod formatter may also note, in a comment or warning, a list of what |
1001 | unrenderable characters were encountered. |
1002 | |
1003 | =item * |
1004 | |
1005 | EE<lt>...> may freely appear in any formatting code (other than |
1006 | in another EE<lt>...> or in an ZE<lt>>). That is, "XE<lt>The |
1007 | EE<lt>euro>1,000,000 Solution>" is valid, as is "LE<lt>The |
1008 | EE<lt>euro>1,000,000 Solution|Million::Euros>". |
1009 | |
1010 | =item * |
1011 | |
3e666715 |
1012 | Some Pod formatters output to formats that implement non-breaking |
8a93676d |
1013 | spaces as an individual character (which I'll call "NBSP"), and |
3e666715 |
1014 | others output to formats that implement non-breaking spaces just as |
8a93676d |
1015 | spaces wrapped in a "don't break this across lines" code. Note that |
1016 | at the level of Pod, both sorts of codes can occur: Pod can contain a |
1017 | NBSP character (whether as a literal, or as a "EE<lt>160>" or |
1018 | "EE<lt>nbsp>" code); and Pod can contain "SE<lt>foo |
1019 | IE<lt>barE<gt> baz>" codes, where "mere spaces" (character 32) in |
3e666715 |
1020 | such codes are taken to represent non-breaking spaces. Pod |
8a93676d |
1021 | parsers should consider supporting the optional parsing of "SE<lt>foo |
1022 | IE<lt>barE<gt> baz>" as if it were |
1023 | "fooI<NBSP>IE<lt>barE<gt>I<NBSP>baz", and, going the other way, the |
1024 | optional parsing of groups of words joined by NBSP's as if each group |
1025 | were in a SE<lt>...> code, so that formatters may use the |
1026 | representation that maps best to what the output format demands. |
1027 | |
1028 | =item * |
1029 | |
210b36aa |
1030 | Some processors may find that the C<SE<lt>...E<gt>> code is easiest to |
8a93676d |
1031 | implement by replacing each space in the parse tree under the content |
1032 | of the S, with an NBSP. But note: the replacement should apply I<not> to |
1033 | spaces in I<all> text, but I<only> to spaces in I<printable> text. (This |
1034 | distinction may or may not be evident in the particular tree/event |
1035 | model implemented by the Pod parser.) For example, consider this |
1036 | unusual case: |
1037 | |
1038 | S<L</Autoloaded Functions>> |
1039 | |
1040 | This means that the space in the middle of the visible link text must |
1041 | not be broken across lines. In other words, it's the same as this: |
1042 | |
1043 | L<"AutoloadedE<160>Functions"/Autoloaded Functions> |
1044 | |
1045 | However, a misapplied space-to-NBSP replacement could (wrongly) |
1046 | produce something equivalent to this: |
1047 | |
1048 | L<"AutoloadedE<160>Functions"/AutoloadedE<160>Functions> |
1049 | |
1050 | ...which is almost definitely not going to work as a hyperlink (assuming |
1051 | this formatter outputs a format supporting hypertext). |
1052 | |
1053 | Formatters may choose to just not support the S format code, |
1054 | especially in cases where the output format simply has no NBSP |
1055 | character/code and no code for "don't break this stuff across lines". |
1056 | |
1057 | =item * |
1058 | |
1059 | Besides the NBSP character discussed above, implementors are reminded |
1060 | of the existence of the other "special" character in Latin-1, the |
210b36aa |
1061 | "soft hyphen" character, also known as "discretionary hyphen", |
8a93676d |
1062 | i.e. C<EE<lt>173E<gt>> = C<EE<lt>0xADE<gt>> = |
1063 | C<EE<lt>shyE<gt>>). This character expresses an optional hyphenation |
1064 | point. That is, it normally renders as nothing, but may render as a |
1065 | "-" if a formatter breaks the word at that point. Pod formatters |
1066 | should, as appropriate, do one of the following: 1) render this with |
1067 | a code with the same meaning (e.g., "\-" in RTF), 2) pass it through |
1068 | in the expectation that the formatter understands this character as |
1069 | such, or 3) delete it. |
1070 | |
1071 | For example: |
1072 | |
1073 | sigE<shy>action |
1074 | manuE<shy>script |
1075 | JarkE<shy>ko HieE<shy>taE<shy>nieE<shy>mi |
1076 | |
1077 | These signal to a formatter that if it is to hyphenate "sigaction" |
1078 | or "manuscript", then it should be done as |
1079 | "sig-I<[linebreak]>action" or "manu-I<[linebreak]>script" |
1080 | (and if it doesn't hyphenate it, then the C<EE<lt>shyE<gt>> doesn't |
1081 | show up at all). And if it is |
1082 | to hyphenate "Jarkko" and/or "Hietaniemi", it can do |
1083 | so only at the points where there is a C<EE<lt>shyE<gt>> code. |
1084 | |
1085 | In practice, it is anticipated that this character will not be used |
1086 | often, but formatters should either support it, or delete it. |
1087 | |
1088 | =item * |
1089 | |
1090 | If you think that you want to add a new command to Pod (like, say, a |
1091 | "=biblio" command), consider whether you could get the same |
1092 | effect with a for or begin/end sequence: "=for biblio ..." or "=begin |
1093 | biblio" ... "=end biblio". Pod processors that don't understand |
1094 | "=for biblio", etc, will simply ignore it, whereas they may complain |
1095 | loudly if they see "=biblio". |
1096 | |
1097 | =item * |
1098 | |
1099 | Throughout this document, "Pod" has been the preferred spelling for |
1100 | the name of the documentation format. One may also use "POD" or |
da75cd15 |
1101 | "pod". For the documentation that is (typically) in the Pod |
8a93676d |
1102 | format, you may use "pod", or "Pod", or "POD". Understanding these |
1103 | distinctions is useful; but obsessing over how to spell them, usually |
1104 | is not. |
1105 | |
1106 | =back |
1107 | |
1108 | |
1109 | |
1110 | |
1111 | |
1112 | =head1 About LE<lt>...E<gt> Codes |
1113 | |
1114 | As you can tell from a glance at L<perlpod|perlpod>, the LE<lt>...> |
1115 | code is the most complex of the Pod formatting codes. The points below |
1116 | will hopefully clarify what it means and how processors should deal |
1117 | with it. |
1118 | |
1119 | =over |
1120 | |
1121 | =item * |
1122 | |
1123 | In parsing an LE<lt>...> code, Pod parsers must distinguish at least |
1124 | four attributes: |
1125 | |
1126 | =over |
1127 | |
1128 | =item First: |
1129 | |
1130 | The link-text. If there is none, this must be undef. (E.g., in |
1131 | "LE<lt>Perl Functions|perlfunc>", the link-text is "Perl Functions". |
1132 | In "LE<lt>Time::HiRes>" and even "LE<lt>|Time::HiRes>", there is no |
1133 | link text. Note that link text may contain formatting.) |
1134 | |
1135 | =item Second: |
1136 | |
ac036724 |
1137 | The possibly inferred link-text; i.e., if there was no real link |
8a93676d |
1138 | text, then this is the text that we'll infer in its place. (E.g., for |
1139 | "LE<lt>Getopt::Std>", the inferred link text is "Getopt::Std".) |
1140 | |
1141 | =item Third: |
1142 | |
1143 | The name or URL, or undef if none. (E.g., in "LE<lt>Perl |
ac036724 |
1144 | Functions|perlfunc>", the name (also sometimes called the page) |
8a93676d |
1145 | is "perlfunc". In "LE<lt>/CAVEATS>", the name is undef.) |
1146 | |
1147 | =item Fourth: |
1148 | |
1149 | The section (AKA "item" in older perlpods), or undef if none. E.g., |
f41e638c |
1150 | in "LE<lt>Getopt::Std/DESCRIPTIONE<gt>", "DESCRIPTION" is the section. (Note |
8a93676d |
1151 | that this is not the same as a manpage section like the "5" in "man 5 |
1152 | crontab". "Section Foo" in the Pod sense means the part of the text |
6edf2346 |
1153 | that's introduced by the heading or item whose text is "Foo".) |
8a93676d |
1154 | |
1155 | =back |
1156 | |
1157 | Pod parsers may also note additional attributes including: |
1158 | |
1159 | =over |
1160 | |
1161 | =item Fifth: |
1162 | |
1163 | A flag for whether item 3 (if present) is a URL (like |
1164 | "http://lists.perl.org" is), in which case there should be no section |
1165 | attribute; a Pod name (like "perldoc" and "Getopt::Std" are); or |
1166 | possibly a man page name (like "crontab(5)" is). |
1167 | |
1168 | =item Sixth: |
1169 | |
1170 | The raw original LE<lt>...> content, before text is split on |
1171 | "|", "/", etc, and before EE<lt>...> codes are expanded. |
1172 | |
1173 | =back |
1174 | |
1175 | (The above were numbered only for concise reference below. It is not |
1176 | a requirement that these be passed as an actual list or array.) |
1177 | |
1178 | For example: |
1179 | |
1180 | L<Foo::Bar> |
1181 | => undef, # link text |
1182 | "Foo::Bar", # possibly inferred link text |
1183 | "Foo::Bar", # name |
1184 | undef, # section |
1185 | 'pod', # what sort of link |
1186 | "Foo::Bar" # original content |
1187 | |
1188 | L<Perlport's section on NL's|perlport/Newlines> |
1189 | => "Perlport's section on NL's", # link text |
1190 | "Perlport's section on NL's", # possibly inferred link text |
1191 | "perlport", # name |
1192 | "Newlines", # section |
1193 | 'pod', # what sort of link |
1194 | "Perlport's section on NL's|perlport/Newlines" # orig. content |
1195 | |
1196 | L<perlport/Newlines> |
1197 | => undef, # link text |
1198 | '"Newlines" in perlport', # possibly inferred link text |
1199 | "perlport", # name |
1200 | "Newlines", # section |
1201 | 'pod', # what sort of link |
1202 | "perlport/Newlines" # original content |
1203 | |
1204 | L<crontab(5)/"DESCRIPTION"> |
1205 | => undef, # link text |
1206 | '"DESCRIPTION" in crontab(5)', # possibly inferred link text |
1207 | "crontab(5)", # name |
1208 | "DESCRIPTION", # section |
1209 | 'man', # what sort of link |
1210 | 'crontab(5)/"DESCRIPTION"' # original content |
1211 | |
1212 | L</Object Attributes> |
1213 | => undef, # link text |
1214 | '"Object Attributes"', # possibly inferred link text |
1215 | undef, # name |
1216 | "Object Attributes", # section |
1217 | 'pod', # what sort of link |
1218 | "/Object Attributes" # original content |
1219 | |
1220 | L<http://www.perl.org/> |
1221 | => undef, # link text |
1222 | "http://www.perl.org/", # possibly inferred link text |
1223 | "http://www.perl.org/", # name |
1224 | undef, # section |
1225 | 'url', # what sort of link |
1226 | "http://www.perl.org/" # original content |
1227 | |
f6e963e4 |
1228 | L<Perl.org|http://www.perl.org/> |
1229 | => "Perl.org", # link text |
1230 | "http://www.perl.org/", # possibly inferred link text |
1231 | "http://www.perl.org/", # name |
1232 | undef, # section |
1233 | 'url', # what sort of link |
1234 | "Perl.org|http://www.perl.org/" # original content |
1235 | |
8a93676d |
1236 | Note that you can distinguish URL-links from anything else by the |
1237 | fact that they match C<m/\A\w+:[^:\s]\S*\z/>. So |
1238 | C<LE<lt>http://www.perl.comE<gt>> is a URL, but |
1239 | C<LE<lt>HTTP::ResponseE<gt>> isn't. |
1240 | |
1241 | =item * |
1242 | |
1243 | In case of LE<lt>...> codes with no "text|" part in them, |
1244 | older formatters have exhibited great variation in actually displaying |
1245 | the link or cross reference. For example, LE<lt>crontab(5)> would render |
1246 | as "the C<crontab(5)> manpage", or "in the C<crontab(5)> manpage" |
1247 | or just "C<crontab(5)>". |
1248 | |
1249 | Pod processors must now treat "text|"-less links as follows: |
1250 | |
1251 | L<name> => L<name|name> |
1252 | L</section> => L<"section"|/section> |
1253 | L<name/section> => L<"section" in name|name/section> |
1254 | |
1255 | =item * |
1256 | |
1257 | Note that section names might contain markup. I.e., if a section |
1258 | starts with: |
1259 | |
1260 | =head2 About the C<-M> Operator |
1261 | |
1262 | or with: |
1263 | |
1264 | =item About the C<-M> Operator |
1265 | |
1266 | then a link to it would look like this: |
1267 | |
1268 | L<somedoc/About the C<-M> Operator> |
1269 | |
1270 | Formatters may choose to ignore the markup for purposes of resolving |
1271 | the link and use only the renderable characters in the section name, |
1272 | as in: |
1273 | |
1274 | <h1><a name="About_the_-M_Operator">About the <code>-M</code> |
1275 | Operator</h1> |
210b36aa |
1276 | |
8a93676d |
1277 | ... |
210b36aa |
1278 | |
8a93676d |
1279 | <a href="somedoc#About_the_-M_Operator">About the <code>-M</code> |
1280 | Operator" in somedoc</a> |
1281 | |
1282 | =item * |
1283 | |
1284 | Previous versions of perlpod distinguished C<LE<lt>name/"section"E<gt>> |
1285 | links from C<LE<lt>name/itemE<gt>> links (and their targets). These |
1286 | have been merged syntactically and semantically in the current |
1287 | specification, and I<section> can refer either to a "=headI<n> Heading |
1288 | Content" command or to a "=item Item Content" command. This |
1289 | specification does not specify what behavior should be in the case |
1290 | of a given document having several things all seeming to produce the |
1291 | same I<section> identifier (e.g., in HTML, several things all producing |
1292 | the same I<anchorname> in <a name="I<anchorname>">...</a> |
1293 | elements). Where Pod processors can control this behavior, they should |
1294 | use the first such anchor. That is, C<LE<lt>Foo/BarE<gt>> refers to the |
1295 | I<first> "Bar" section in Foo. |
1296 | |
1297 | But for some processors/formats this cannot be easily controlled; as |
1298 | with the HTML example, the behavior of multiple ambiguous |
1299 | <a name="I<anchorname>">...</a> is most easily just left up to |
1300 | browsers to decide. |
1301 | |
1302 | =item * |
1303 | |
1304 | Authors wanting to link to a particular (absolute) URL, must do so |
1305 | only with "LE<lt>scheme:...>" codes (like |
1306 | LE<lt>http://www.perl.org>), and must not attempt "LE<lt>Some Site |
1307 | Name|scheme:...>" codes. This restriction avoids many problems |
1308 | in parsing and rendering LE<lt>...> codes. |
1309 | |
1310 | =item * |
1311 | |
1312 | In a C<LE<lt>text|...E<gt>> code, text may contain formatting codes |
1313 | for formatting or for EE<lt>...> escapes, as in: |
1314 | |
1315 | L<B<ummE<234>stuff>|...> |
1316 | |
1317 | For C<LE<lt>...E<gt>> codes without a "name|" part, only |
ac036724 |
1318 | C<EE<lt>...E<gt>> and C<ZE<lt>E<gt>> codes may occur. That is, |
1319 | authors should not use "C<LE<lt>BE<lt>Foo::BarE<gt>E<gt>>". |
8a93676d |
1320 | |
1321 | Note, however, that formatting codes and ZE<lt>>'s can occur in any |
1322 | and all parts of an LE<lt>...> (i.e., in I<name>, I<section>, I<text>, |
1323 | and I<url>). |
1324 | |
1325 | Authors must not nest LE<lt>...> codes. For example, "LE<lt>The |
1326 | LE<lt>Foo::Bar> man page>" should be treated as an error. |
1327 | |
1328 | =item * |
1329 | |
1330 | Note that Pod authors may use formatting codes inside the "text" |
1331 | part of "LE<lt>text|name>" (and so on for LE<lt>text|/"sec">). |
1332 | |
1333 | In other words, this is valid: |
1334 | |
1335 | Go read L<the docs on C<$.>|perlvar/"$."> |
1336 | |
1337 | Some output formats that do allow rendering "LE<lt>...>" codes as |
1338 | hypertext, might not allow the link-text to be formatted; in |
1339 | that case, formatters will have to just ignore that formatting. |
1340 | |
1341 | =item * |
1342 | |
1343 | At time of writing, C<LE<lt>nameE<gt>> values are of two types: |
1344 | either the name of a Pod page like C<LE<lt>Foo::BarE<gt>> (which |
1345 | might be a real Perl module or program in an @INC / PATH |
e1020413 |
1346 | directory, or a .pod file in those places); or the name of a Unix |
8a93676d |
1347 | man page, like C<LE<lt>crontab(5)E<gt>>. In theory, C<LE<lt>chmodE<gt>> |
1348 | in ambiguous between a Pod page called "chmod", or the Unix man page |
1349 | "chmod" (in whatever man-section). However, the presence of a string |
1350 | in parens, as in "crontab(5)", is sufficient to signal that what |
1351 | is being discussed is not a Pod page, and so is presumably a |
e1020413 |
1352 | Unix man page. The distinction is of no importance to many |
8a93676d |
1353 | Pod processors, but some processors that render to hypertext formats |
1354 | may need to distinguish them in order to know how to render a |
1355 | given C<LE<lt>fooE<gt>> code. |
1356 | |
1357 | =item * |
1358 | |
b41aadf2 |
1359 | Previous versions of perlpod allowed for a C<LE<lt>sectionE<gt>> syntax (as in |
1360 | C<LE<lt>Object AttributesE<gt>>), which was not easily distinguishable from |
1361 | C<LE<lt>nameE<gt>> syntax and for C<LE<lt>"section"E<gt>> which was only |
1362 | slightly less ambiguous. This syntax is no longer in the specification, and |
1363 | has been replaced by the C<LE<lt>/sectionE<gt>> syntax (where the slash was |
1364 | formerly optional). Pod parsers should tolerate the C<LE<lt>"section"E<gt>> |
1365 | syntax, for a while at least. The suggested heuristic for distinguishing |
1366 | C<LE<lt>sectionE<gt>> from C<LE<lt>nameE<gt>> is that if it contains any |
1367 | whitespace, it's a I<section>. Pod processors should warn about this being |
1368 | deprecated syntax. |
8a93676d |
1369 | |
1370 | =back |
1371 | |
1372 | =head1 About =over...=back Regions |
1373 | |
1374 | "=over"..."=back" regions are used for various kinds of list-like |
1375 | structures. (I use the term "region" here simply as a collective |
1376 | term for everything from the "=over" to the matching "=back".) |
1377 | |
1378 | =over |
1379 | |
1380 | =item * |
1381 | |
1382 | The non-zero numeric I<indentlevel> in "=over I<indentlevel>" ... |
1383 | "=back" is used for giving the formatter a clue as to how many |
1384 | "spaces" (ems, or roughly equivalent units) it should tab over, |
1385 | although many formatters will have to convert this to an absolute |
1386 | measurement that may not exactly match with the size of spaces (or M's) |
1387 | in the document's base font. Other formatters may have to completely |
1388 | ignore the number. The lack of any explicit I<indentlevel> parameter is |
1389 | equivalent to an I<indentlevel> value of 4. Pod processors may |
1390 | complain if I<indentlevel> is present but is not a positive number |
1391 | matching C<m/\A(\d*\.)?\d+\z/>. |
1392 | |
1393 | =item * |
1394 | |
1395 | Authors of Pod formatters are reminded that "=over" ... "=back" may |
1396 | map to several different constructs in your output format. For |
1397 | example, in converting Pod to (X)HTML, it can map to any of |
1398 | <ul>...</ul>, <ol>...</ol>, <dl>...</dl>, or |
1399 | <blockquote>...</blockquote>. Similarly, "=item" can map to <li> or |
1400 | <dt>. |
1401 | |
1402 | =item * |
1403 | |
1404 | Each "=over" ... "=back" region should be one of the following: |
1405 | |
1406 | =over |
1407 | |
1408 | =item * |
1409 | |
1410 | An "=over" ... "=back" region containing only "=item *" commands, |
1411 | each followed by some number of ordinary/verbatim paragraphs, other |
1412 | nested "=over" ... "=back" regions, "=for..." paragraphs, and |
1413 | "=begin"..."=end" regions. |
1414 | |
1415 | (Pod processors must tolerate a bare "=item" as if it were "=item |
1416 | *".) Whether "*" is rendered as a literal asterisk, an "o", or as |
1417 | some kind of real bullet character, is left up to the Pod formatter, |
1418 | and may depend on the level of nesting. |
1419 | |
1420 | =item * |
1421 | |
1422 | An "=over" ... "=back" region containing only |
1423 | C<m/\A=item\s+\d+\.?\s*\z/> paragraphs, each one (or each group of them) |
1424 | followed by some number of ordinary/verbatim paragraphs, other nested |
1425 | "=over" ... "=back" regions, "=for..." paragraphs, and/or |
1426 | "=begin"..."=end" codes. Note that the numbers must start at 1 |
1427 | in each section, and must proceed in order and without skipping |
1428 | numbers. |
1429 | |
1430 | (Pod processors must tolerate lines like "=item 1" as if they were |
1431 | "=item 1.", with the period.) |
1432 | |
1433 | =item * |
1434 | |
1435 | An "=over" ... "=back" region containing only "=item [text]" |
1436 | commands, each one (or each group of them) followed by some number of |
1437 | ordinary/verbatim paragraphs, other nested "=over" ... "=back" |
1438 | regions, or "=for..." paragraphs, and "=begin"..."=end" regions. |
1439 | |
1440 | The "=item [text]" paragraph should not match |
1441 | C<m/\A=item\s+\d+\.?\s*\z/> or C<m/\A=item\s+\*\s*\z/>, nor should it |
1442 | match just C<m/\A=item\s*\z/>. |
1443 | |
1444 | =item * |
1445 | |
1446 | An "=over" ... "=back" region containing no "=item" paragraphs at |
1447 | all, and containing only some number of |
1448 | ordinary/verbatim paragraphs, and possibly also some nested "=over" |
1449 | ... "=back" regions, "=for..." paragraphs, and "=begin"..."=end" |
1450 | regions. Such an itemless "=over" ... "=back" region in Pod is |
1451 | equivalent in meaning to a "<blockquote>...</blockquote>" element in |
1452 | HTML. |
1453 | |
1454 | =back |
1455 | |
1456 | Note that with all the above cases, you can determine which type of |
1457 | "=over" ... "=back" you have, by examining the first (non-"=cut", |
1458 | non-"=pod") Pod paragraph after the "=over" command. |
1459 | |
1460 | =item * |
1461 | |
1462 | Pod formatters I<must> tolerate arbitrarily large amounts of text |
1463 | in the "=item I<text...>" paragraph. In practice, most such |
1464 | paragraphs are short, as in: |
1465 | |
1466 | =item For cutting off our trade with all parts of the world |
1467 | |
1468 | But they may be arbitrarily long: |
1469 | |
1470 | =item For transporting us beyond seas to be tried for pretended |
1471 | offenses |
1472 | |
1473 | =item He is at this time transporting large armies of foreign |
1474 | mercenaries to complete the works of death, desolation and |
1475 | tyranny, already begun with circumstances of cruelty and perfidy |
1476 | scarcely paralleled in the most barbarous ages, and totally |
1477 | unworthy the head of a civilized nation. |
1478 | |
1479 | =item * |
1480 | |
1481 | Pod processors should tolerate "=item *" / "=item I<number>" commands |
1482 | with no accompanying paragraph. The middle item is an example: |
1483 | |
1484 | =over |
210b36aa |
1485 | |
8a93676d |
1486 | =item 1 |
210b36aa |
1487 | |
8a93676d |
1488 | Pick up dry cleaning. |
210b36aa |
1489 | |
8a93676d |
1490 | =item 2 |
210b36aa |
1491 | |
8a93676d |
1492 | =item 3 |
210b36aa |
1493 | |
8a93676d |
1494 | Stop by the store. Get Abba Zabas, Stoli, and cheap lawn chairs. |
210b36aa |
1495 | |
8a93676d |
1496 | =back |
1497 | |
1498 | =item * |
1499 | |
1500 | No "=over" ... "=back" region can contain headings. Processors may |
1501 | treat such a heading as an error. |
1502 | |
1503 | =item * |
1504 | |
1505 | Note that an "=over" ... "=back" region should have some |
1506 | content. That is, authors should not have an empty region like this: |
1507 | |
1508 | =over |
210b36aa |
1509 | |
8a93676d |
1510 | =back |
1511 | |
1512 | Pod processors seeing such a contentless "=over" ... "=back" region, |
1513 | may ignore it, or may report it as an error. |
1514 | |
1515 | =item * |
1516 | |
1517 | Processors must tolerate an "=over" list that goes off the end of the |
1518 | document (i.e., which has no matching "=back"), but they may warn |
1519 | about such a list. |
1520 | |
1521 | =item * |
1522 | |
1523 | Authors of Pod formatters should note that this construct: |
1524 | |
1525 | =item Neque |
1526 | |
1527 | =item Porro |
1528 | |
1529 | =item Quisquam Est |
210b36aa |
1530 | |
8a93676d |
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 | =item Ut Enim |
1536 | |
1537 | is semantically ambiguous, in a way that makes formatting decisions |
1538 | a bit difficult. On the one hand, it could be mention of an item |
1539 | "Neque", mention of another item "Porro", and mention of another |
1540 | item "Quisquam Est", with just the last one requiring the explanatory |
1541 | paragraph "Qui dolorem ipsum quia dolor..."; and then an item |
1542 | "Ut Enim". In that case, you'd want to format it like so: |
1543 | |
1544 | Neque |
210b36aa |
1545 | |
8a93676d |
1546 | Porro |
210b36aa |
1547 | |
8a93676d |
1548 | Quisquam Est |
1549 | Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci |
1550 | velit, sed quia non numquam eius modi tempora incidunt ut |
1551 | labore et dolore magnam aliquam quaerat voluptatem. |
1552 | |
1553 | Ut Enim |
1554 | |
1555 | But it could equally well be a discussion of three (related or equivalent) |
1556 | items, "Neque", "Porro", and "Quisquam Est", followed by a paragraph |
1557 | explaining them all, and then a new item "Ut Enim". In that case, you'd |
1558 | probably want to format it like so: |
1559 | |
1560 | Neque |
1561 | Porro |
1562 | Quisquam Est |
1563 | Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci |
1564 | velit, sed quia non numquam eius modi tempora incidunt ut |
1565 | labore et dolore magnam aliquam quaerat voluptatem. |
1566 | |
1567 | Ut Enim |
1568 | |
353c6505 |
1569 | But (for the foreseeable future), Pod does not provide any way for Pod |
8a93676d |
1570 | authors to distinguish which grouping is meant by the above |
1571 | "=item"-cluster structure. So formatters should format it like so: |
1572 | |
1573 | Neque |
1574 | |
1575 | Porro |
1576 | |
1577 | Quisquam Est |
1578 | |
1579 | Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci |
1580 | velit, sed quia non numquam eius modi tempora incidunt ut |
1581 | labore et dolore magnam aliquam quaerat voluptatem. |
1582 | |
1583 | Ut Enim |
1584 | |
210b36aa |
1585 | That is, there should be (at least roughly) equal spacing between |
8a93676d |
1586 | items as between paragraphs (although that spacing may well be less |
1587 | than the full height of a line of text). This leaves it to the reader |
1588 | to use (con)textual cues to figure out whether the "Qui dolorem |
1589 | ipsum..." paragraph applies to the "Quisquam Est" item or to all three |
1590 | items "Neque", "Porro", and "Quisquam Est". While not an ideal |
1591 | situation, this is preferable to providing formatting cues that may |
1592 | be actually contrary to the author's intent. |
1593 | |
1594 | =back |
1595 | |
1596 | |
1597 | |
1598 | =head1 About Data Paragraphs and "=begin/=end" Regions |
1599 | |
1600 | Data paragraphs are typically used for inlining non-Pod data that is |
1601 | to be used (typically passed through) when rendering the document to |
1602 | a specific format: |
1603 | |
1604 | =begin rtf |
210b36aa |
1605 | |
8a93676d |
1606 | \par{\pard\qr\sa4500{\i Printed\~\chdate\~\chtime}\par} |
210b36aa |
1607 | |
8a93676d |
1608 | =end rtf |
1609 | |
1610 | The exact same effect could, incidentally, be achieved with a single |
1611 | "=for" paragraph: |
1612 | |
1613 | =for rtf \par{\pard\qr\sa4500{\i Printed\~\chdate\~\chtime}\par} |
1614 | |
1615 | (Although that is not formally a data paragraph, it has the same |
1616 | meaning as one, and Pod parsers may parse it as one.) |
1617 | |
1618 | Another example of a data paragraph: |
1619 | |
1620 | =begin html |
210b36aa |
1621 | |
8a93676d |
1622 | I like <em>PIE</em>! |
210b36aa |
1623 | |
8a93676d |
1624 | <hr>Especially pecan pie! |
210b36aa |
1625 | |
8a93676d |
1626 | =end html |
1627 | |
1628 | If these were ordinary paragraphs, the Pod parser would try to |
1629 | expand the "EE<lt>/em>" (in the first paragraph) as a formatting |
1630 | code, just like "EE<lt>lt>" or "EE<lt>eacute>". But since this |
1631 | is in a "=begin I<identifier>"..."=end I<identifier>" region I<and> |
1632 | the identifier "html" doesn't begin have a ":" prefix, the contents |
1633 | of this region are stored as data paragraphs, instead of being |
1634 | processed as ordinary paragraphs (or if they began with a spaces |
1635 | and/or tabs, as verbatim paragraphs). |
1636 | |
1637 | As a further example: At time of writing, no "biblio" identifier is |
1638 | supported, but suppose some processor were written to recognize it as |
1639 | a way of (say) denoting a bibliographic reference (necessarily |
1640 | containing formatting codes in ordinary paragraphs). The fact that |
1641 | "biblio" paragraphs were meant for ordinary processing would be |
1642 | indicated by prefacing each "biblio" identifier with a colon: |
1643 | |
1644 | =begin :biblio |
1645 | |
1646 | Wirth, Niklaus. 1976. I<Algorithms + Data Structures = |
1647 | Programs.> Prentice-Hall, Englewood Cliffs, NJ. |
1648 | |
1649 | =end :biblio |
1650 | |
1651 | This would signal to the parser that paragraphs in this begin...end |
1652 | region are subject to normal handling as ordinary/verbatim paragraphs |
1653 | (while still tagged as meant only for processors that understand the |
1654 | "biblio" identifier). The same effect could be had with: |
1655 | |
1656 | =for :biblio |
1657 | Wirth, Niklaus. 1976. I<Algorithms + Data Structures = |
1658 | Programs.> Prentice-Hall, Englewood Cliffs, NJ. |
1659 | |
1660 | The ":" on these identifiers means simply "process this stuff |
1661 | normally, even though the result will be for some special target". |
1662 | I suggest that parser APIs report "biblio" as the target identifier, |
1663 | but also report that it had a ":" prefix. (And similarly, with the |
1664 | above "html", report "html" as the target identifier, and note the |
1665 | I<lack> of a ":" prefix.) |
1666 | |
1667 | Note that a "=begin I<identifier>"..."=end I<identifier>" region where |
1668 | I<identifier> begins with a colon, I<can> contain commands. For example: |
1669 | |
1670 | =begin :biblio |
210b36aa |
1671 | |
8a93676d |
1672 | Wirth's classic is available in several editions, including: |
210b36aa |
1673 | |
8a93676d |
1674 | =for comment |
1675 | hm, check abebooks.com for how much used copies cost. |
210b36aa |
1676 | |
8a93676d |
1677 | =over |
210b36aa |
1678 | |
8a93676d |
1679 | =item |
210b36aa |
1680 | |
8a93676d |
1681 | Wirth, Niklaus. 1975. I<Algorithmen und Datenstrukturen.> |
1682 | Teubner, Stuttgart. [Yes, it's in German.] |
210b36aa |
1683 | |
8a93676d |
1684 | =item |
210b36aa |
1685 | |
8a93676d |
1686 | Wirth, Niklaus. 1976. I<Algorithms + Data Structures = |
1687 | Programs.> Prentice-Hall, Englewood Cliffs, NJ. |
210b36aa |
1688 | |
8a93676d |
1689 | =back |
210b36aa |
1690 | |
8a93676d |
1691 | =end :biblio |
1692 | |
1693 | Note, however, a "=begin I<identifier>"..."=end I<identifier>" |
1694 | region where I<identifier> does I<not> begin with a colon, should not |
1695 | directly contain "=head1" ... "=head4" commands, nor "=over", nor "=back", |
1696 | nor "=item". For example, this may be considered invalid: |
1697 | |
1698 | =begin somedata |
210b36aa |
1699 | |
8a93676d |
1700 | This is a data paragraph. |
210b36aa |
1701 | |
8a93676d |
1702 | =head1 Don't do this! |
210b36aa |
1703 | |
8a93676d |
1704 | This is a data paragraph too. |
210b36aa |
1705 | |
8a93676d |
1706 | =end somedata |
1707 | |
1708 | A Pod processor may signal that the above (specifically the "=head1" |
1709 | paragraph) is an error. Note, however, that the following should |
1710 | I<not> be treated as an error: |
1711 | |
1712 | =begin somedata |
210b36aa |
1713 | |
8a93676d |
1714 | This is a data paragraph. |
210b36aa |
1715 | |
8a93676d |
1716 | =cut |
210b36aa |
1717 | |
8a93676d |
1718 | # Yup, this isn't Pod anymore. |
1719 | sub excl { (rand() > .5) ? "hoo!" : "hah!" } |
210b36aa |
1720 | |
8a93676d |
1721 | =pod |
210b36aa |
1722 | |
8a93676d |
1723 | This is a data paragraph too. |
210b36aa |
1724 | |
8a93676d |
1725 | =end somedata |
1726 | |
1727 | And this too is valid: |
1728 | |
1729 | =begin someformat |
210b36aa |
1730 | |
8a93676d |
1731 | This is a data paragraph. |
210b36aa |
1732 | |
8a93676d |
1733 | And this is a data paragraph. |
210b36aa |
1734 | |
8a93676d |
1735 | =begin someotherformat |
210b36aa |
1736 | |
8a93676d |
1737 | This is a data paragraph too. |
210b36aa |
1738 | |
8a93676d |
1739 | And this is a data paragraph too. |
210b36aa |
1740 | |
8a93676d |
1741 | =begin :yetanotherformat |
1742 | |
1743 | =head2 This is a command paragraph! |
1744 | |
1745 | This is an ordinary paragraph! |
210b36aa |
1746 | |
8a93676d |
1747 | And this is a verbatim paragraph! |
210b36aa |
1748 | |
8a93676d |
1749 | =end :yetanotherformat |
210b36aa |
1750 | |
8a93676d |
1751 | =end someotherformat |
210b36aa |
1752 | |
8a93676d |
1753 | Another data paragraph! |
210b36aa |
1754 | |
8a93676d |
1755 | =end someformat |
1756 | |
1757 | The contents of the above "=begin :yetanotherformat" ... |
1758 | "=end :yetanotherformat" region I<aren't> data paragraphs, because |
1759 | the immediately containing region's identifier (":yetanotherformat") |
1760 | begins with a colon. In practice, most regions that contain |
1761 | data paragraphs will contain I<only> data paragraphs; however, |
1762 | the above nesting is syntactically valid as Pod, even if it is |
1763 | rare. However, the handlers for some formats, like "html", |
1764 | will accept only data paragraphs, not nested regions; and they may |
1765 | complain if they see (targeted for them) nested regions, or commands, |
1766 | other than "=end", "=pod", and "=cut". |
1767 | |
1768 | Also consider this valid structure: |
1769 | |
1770 | =begin :biblio |
210b36aa |
1771 | |
8a93676d |
1772 | Wirth's classic is available in several editions, including: |
210b36aa |
1773 | |
8a93676d |
1774 | =over |
210b36aa |
1775 | |
8a93676d |
1776 | =item |
210b36aa |
1777 | |
8a93676d |
1778 | Wirth, Niklaus. 1975. I<Algorithmen und Datenstrukturen.> |
1779 | Teubner, Stuttgart. [Yes, it's in German.] |
210b36aa |
1780 | |
8a93676d |
1781 | =item |
210b36aa |
1782 | |
8a93676d |
1783 | Wirth, Niklaus. 1976. I<Algorithms + Data Structures = |
1784 | Programs.> Prentice-Hall, Englewood Cliffs, NJ. |
1785 | |
1786 | =back |
210b36aa |
1787 | |
8a93676d |
1788 | Buy buy buy! |
210b36aa |
1789 | |
8a93676d |
1790 | =begin html |
210b36aa |
1791 | |
8a93676d |
1792 | <img src='wirth_spokesmodeling_book.png'> |
210b36aa |
1793 | |
8a93676d |
1794 | <hr> |
210b36aa |
1795 | |
8a93676d |
1796 | =end html |
210b36aa |
1797 | |
8a93676d |
1798 | Now now now! |
210b36aa |
1799 | |
8a93676d |
1800 | =end :biblio |
1801 | |
1802 | There, the "=begin html"..."=end html" region is nested inside |
1803 | the larger "=begin :biblio"..."=end :biblio" region. Note that the |
1804 | content of the "=begin html"..."=end html" region is data |
1805 | paragraph(s), because the immediately containing region's identifier |
1806 | ("html") I<doesn't> begin with a colon. |
1807 | |
1808 | Pod parsers, when processing a series of data paragraphs one |
1809 | after another (within a single region), should consider them to |
1810 | be one large data paragraph that happens to contain blank lines. So |
1811 | the content of the above "=begin html"..."=end html" I<may> be stored |
1812 | as two data paragraphs (one consisting of |
1813 | "<img src='wirth_spokesmodeling_book.png'>\n" |
1814 | and another consisting of "<hr>\n"), but I<should> be stored as |
1815 | a single data paragraph (consisting of |
1816 | "<img src='wirth_spokesmodeling_book.png'>\n\n<hr>\n"). |
1817 | |
1818 | Pod processors should tolerate empty |
1819 | "=begin I<something>"..."=end I<something>" regions, |
1820 | empty "=begin :I<something>"..."=end :I<something>" regions, and |
1821 | contentless "=for I<something>" and "=for :I<something>" |
1822 | paragraphs. I.e., these should be tolerated: |
1823 | |
1824 | =for html |
210b36aa |
1825 | |
8a93676d |
1826 | =begin html |
210b36aa |
1827 | |
8a93676d |
1828 | =end html |
210b36aa |
1829 | |
8a93676d |
1830 | =begin :biblio |
210b36aa |
1831 | |
8a93676d |
1832 | =end :biblio |
1833 | |
1834 | Incidentally, note that there's no easy way to express a data |
1835 | paragraph starting with something that looks like a command. Consider: |
1836 | |
1837 | =begin stuff |
210b36aa |
1838 | |
8a93676d |
1839 | =shazbot |
210b36aa |
1840 | |
8a93676d |
1841 | =end stuff |
1842 | |
1843 | There, "=shazbot" will be parsed as a Pod command "shazbot", not as a data |
1844 | paragraph "=shazbot\n". However, you can express a data paragraph consisting |
1845 | of "=shazbot\n" using this code: |
1846 | |
1847 | =for stuff =shazbot |
1848 | |
1849 | The situation where this is necessary, is presumably quite rare. |
1850 | |
1851 | Note that =end commands must match the currently open =begin command. That |
1852 | is, they must properly nest. For example, this is valid: |
1853 | |
1854 | =begin outer |
210b36aa |
1855 | |
8a93676d |
1856 | X |
210b36aa |
1857 | |
8a93676d |
1858 | =begin inner |
210b36aa |
1859 | |
8a93676d |
1860 | Y |
210b36aa |
1861 | |
8a93676d |
1862 | =end inner |
210b36aa |
1863 | |
8a93676d |
1864 | Z |
210b36aa |
1865 | |
8a93676d |
1866 | =end outer |
1867 | |
1868 | while this is invalid: |
1869 | |
1870 | =begin outer |
210b36aa |
1871 | |
8a93676d |
1872 | X |
210b36aa |
1873 | |
8a93676d |
1874 | =begin inner |
210b36aa |
1875 | |
8a93676d |
1876 | Y |
210b36aa |
1877 | |
8a93676d |
1878 | =end outer |
210b36aa |
1879 | |
8a93676d |
1880 | Z |
210b36aa |
1881 | |
8a93676d |
1882 | =end inner |
210b36aa |
1883 | |
8a93676d |
1884 | This latter is improper because when the "=end outer" command is seen, the |
1885 | currently open region has the formatname "inner", not "outer". (It just |
1886 | happens that "outer" is the format name of a higher-up region.) This is |
1887 | an error. Processors must by default report this as an error, and may halt |
210b36aa |
1888 | processing the document containing that error. A corollary of this is that |
ac036724 |
1889 | regions cannot "overlap". That is, the latter block above does not represent |
8a93676d |
1890 | a region called "outer" which contains X and Y, overlapping a region called |
1891 | "inner" which contains Y and Z. But because it is invalid (as all |
1892 | apparently overlapping regions would be), it doesn't represent that, or |
1893 | anything at all. |
1894 | |
1895 | Similarly, this is invalid: |
1896 | |
1897 | =begin thing |
210b36aa |
1898 | |
8a93676d |
1899 | =end hting |
1900 | |
1901 | This is an error because the region is opened by "thing", and the "=end" |
1902 | tries to close "hting" [sic]. |
1903 | |
1904 | This is also invalid: |
1905 | |
1906 | =begin thing |
210b36aa |
1907 | |
8a93676d |
1908 | =end |
1909 | |
1910 | This is invalid because every "=end" command must have a formatname |
1911 | parameter. |
1912 | |
1913 | =head1 SEE ALSO |
1914 | |
1915 | L<perlpod>, L<perlsyn/"PODs: Embedded Documentation">, |
1916 | L<podchecker> |
1917 | |
1918 | =head1 AUTHOR |
1919 | |
1920 | Sean M. Burke |
1921 | |
1922 | =cut |
1923 | |
1924 | |