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01496481 | 1 | $Cambridge: exim/doc/doc-docbook/HowItWorks.txt,v 1.9 2008/02/04 17:28:44 fanf2 Exp $ |
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2 | |
3 | CREATING THE EXIM DOCUMENTATION | |
4 | ||
5 | "You are lost in a maze of twisty little scripts." | |
6 | ||
7 | ||
8 | This document describes how the various versions of the Exim documentation, in | |
9 | different output formats, are created from DocBook XML, and also how the | |
10 | DocBook XML is itself created. | |
11 | ||
12 | ||
13 | BACKGROUND: THE OLD WAY | |
14 | ||
15 | From the start of Exim, in 1995, the specification was written in a local text | |
16 | formatting system known as SGCAL. This is capable of producing PostScript and | |
17 | plain text output from the same source file. Later, when the "ps2pdf" command | |
18 | became available with GhostScript, that was used to create a PDF version from | |
19 | the PostScript. (A few earlier versions were created by a helpful user who had | |
20 | bought the Adobe distiller software.) | |
21 | ||
22 | A demand for a version in "info" format led me to write a Perl script that | |
23 | converted the SGCAL input into a Texinfo file. Because of the somewhat | |
f89d2485 | 24 | restrictive requirements of Texinfo, this script always needed a lot of |
9b371988 | 25 | maintenance, and was never totally satisfactory. |
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26 | |
27 | The HTML version of the documentation was originally produced from the Texinfo | |
28 | version, but later I wrote another Perl script that produced it directly from | |
29 | the SGCAL input, which made it possible to produce better HTML. | |
30 | ||
31 | There were a small number of diagrams in the documentation. For the PostScript | |
32 | and PDF versions, these were created using Aspic, a local text-driven drawing | |
33 | program that interfaces directly to SGCAL. For the text and texinfo versions, | |
34 | alternative ascii-art diagrams were used. For the HTML version, screen shots of | |
35 | the PostScript output were turned into gifs. | |
36 | ||
37 | ||
38 | A MORE STANDARD APPROACH | |
39 | ||
40 | Although in principle SGCAL and Aspic could be generally released, they would | |
41 | be unlikely to receive much (if any) maintenance, especially after I retire. | |
42 | Furthermore, the old production method was only semi-automatic; I still did a | |
43 | certain amount of hand tweaking of spec.txt, for example. As the maintenance of | |
44 | Exim itself was being opened up to a larger group of people, it seemed sensible | |
45 | to move to a more standard way of producing the documentation, preferable fully | |
46 | automated. However, we wanted to use only non-commercial software to do this. | |
47 | ||
48 | At the time I was thinking about converting (early 2005), the "obvious" | |
49 | standard format in which to keep the documentation was DocBook XML. The use of | |
50 | XML in general, in many different applications, was increasing rapidly, and it | |
51 | seemed likely to remain a standard for some time to come. DocBook offered a | |
52 | particular form of XML suited to documents that were effectively "books". | |
53 | ||
54 | Maintaining an XML document by hand editing is a tedious, verbose, and | |
55 | error-prone process. A number of specialized XML text editors were available, | |
56 | but all the free ones were at a very primitive stage. I therefore decided to | |
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57 | keep the master source in AsciiDoc format, from which a secondary XML master |
58 | could be automatically generated. | |
59 | ||
60 | The first "new" versions of the documents, for the 4.60 release, were generated | |
61 | this way. However, there were a number of problems with using AsciiDoc for a | |
62 | document as large and as complex as the Exim manual. As a result, I wrote a new | |
63 | application called xfpt ("XML From Plain Text") which creates XML from a | |
64 | relatively simple and consistent markup language. This application has been | |
65 | released for general use, and the master sources for the Exim documentation are | |
66 | now in xfpt format. | |
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67 | |
68 | All the output formats are generated from the XML file. If, in the future, a | |
69 | better way of maintaining the XML source becomes available, this can be adopted | |
70 | without changing any of the processing that produces the output documents. | |
71 | Equally, if better ways of processing the XML become available, they can be | |
72 | adopted without affecting the source maintenance. | |
73 | ||
74 | A number of issues arose while setting this all up, which are best summed up by | |
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75 | the statement that a lot of the technology was (in 2006) still very immature. |
76 | Trying to do this conversion any earlier would probably not have been anywhere | |
e492cc8d | 77 | near as successful. The main issues that bother me in the XML-generated |
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78 | documentation are described in the penultimate section of this document. |
79 | ||
e492cc8d | 80 | Initially, the major problems were in producing PostScript and PDF outputs. The |
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81 | available free software for doing this was and still is (we are now in 2007) |
82 | cumbersome and slow, and does not support certain output features that I would | |
83 | like. My response to this was, over a period of two years, to write an XML | |
84 | processor called SDoP (Simple DocBook Processor). This program reads DocBook | |
85 | XML and writes PostScript, without using any of the heavyweight apparatus that | |
86 | is required for xmlto and fop (the previously used software). | |
87 | ||
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88 | An experimental first version of SDoP was used for the Exim 4.67 |
89 | documentation. Subsequently SDoP was released for general use. SDoP's output | |
f89d2485 | 90 | includes features that are missing when xmlto/fop is used, and it also runs |
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91 | about 60 times faster. The main manual can be formatted in 2.5 seconds instead |
92 | of 2.5 minutes, which makes checking and fixing mistakes much easier. | |
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93 | |
94 | The Makefile that is used to build the various forms of output will, for the | |
95 | moment, support both ways of producing PostScript and PDF output, though the | |
96 | default is now to use SDoP. | |
168e428f | 97 | |
9b371988 | 98 | The following sections describe the processes by which the xfpt files are |
168e428f | 99 | transformed into the final output documents. In practice, the details are coded |
9b371988 | 100 | into a Makefile that specifies the chain of commands for each output format. |
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101 | |
102 | ||
103 | REQUIRED SOFTWARE | |
104 | ||
105 | Installing software to process XML puts lots and lots of stuff on your box. I | |
106 | run Gentoo Linux, and a lot of things have been installed as dependencies that | |
107 | I am not fully aware of. This is what I know about (version numbers are current | |
108 | at the time of writing): | |
109 | ||
e492cc8d | 110 | . xfpt 0.03 |
168e428f | 111 | |
9b371988 | 112 | This converts the master source file into a DocBook XML file. |
168e428f | 113 | |
e492cc8d | 114 | . sdop 0.03 |
f89d2485 | 115 | |
e492cc8d | 116 | This is my new DocBook-to-PostScript processor. |
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117 | |
118 | . ps2pdf | |
119 | ||
120 | This is a wrapper script that is part of the GhostScript distribution. It | |
121 | converts a PostScript file into a PDF file. It is used to process the output | |
122 | from SDoP. It is not required when xmlto/fop is being used to generate PDF | |
123 | output. | |
124 | ||
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125 | . xmlto 0.0.18 |
126 | ||
127 | This is a shell script that drives various XML processors. It is used to | |
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128 | produce "formatted objects" when PostScript and PDF output is being generated |
129 | using fop (the old way) rather than SDoP. It is always used to produce HTML | |
130 | output. It uses xsltproc, libxml, libxslt, libexslt, and possibly other | |
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131 | things that I have not figured out, to apply the DocBook XSLT stylesheets. |
132 | ||
133 | . libxml 1.8.17 | |
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134 | libxml2 2.6.28 |
135 | libxslt 1.1.20 | |
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136 | |
137 | These are all installed on my box; I do not know which of libxml or libxml2 | |
138 | the various scripts are actually using. | |
139 | ||
f89d2485 | 140 | . xsl-stylesheets-1.70.1 |
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141 | |
142 | These are the standard DocBook XSL stylesheets. | |
143 | ||
e492cc8d | 144 | . fop 0.93 |
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145 | |
146 | FOP is a processor for "formatted objects". It is written in Java. The fop | |
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147 | command is a shell script that drives it. It required only if you do not |
148 | want to use SDoP and ps2pdf to generate PostScript and PDF output. | |
168e428f | 149 | |
e492cc8d | 150 | . w3m 0.5.2 |
168e428f | 151 | |
595028e4 | 152 | This is a text-oriented web brower. It is used to produce the ASCII form of |
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153 | the Exim documentation (spec.txt) from a specially-created HTML format. It |
154 | seems to do a better job than lynx. | |
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155 | |
156 | . docbook2texi (part of docbook2X 0.8.5) | |
157 | ||
158 | This is a wrapper script for a two-stage conversion process from DocBook to a | |
159 | Texinfo file. It uses db2x_xsltproc and db2x_texixml. Unfortunately, there | |
160 | are two versions of this command; the old one is based on an earlier fork of | |
161 | docbook2X and does not work. | |
162 | ||
163 | . db2x_xsltproc and db2x_texixml (part of docbook2X 0.8.5) | |
164 | ||
165 | More wrapping scripts (see previous item). | |
166 | ||
167 | . makeinfo 4.8 | |
168 | ||
e492cc8d | 169 | This is used to make an "info" file from a Texinfo file. |
168e428f | 170 | |
9b371988 PH |
171 | In addition, there are a number of locally written Perl scripts. These are |
172 | described below. | |
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173 | |
174 | ||
175 | THE MAKEFILE | |
176 | ||
177 | The makefile supports a number of targets of the form x.y, where x is one of | |
178 | "filter", "spec", or "test", and y is one of "xml", "fo", "ps", "pdf", "html", | |
179 | "txt", or "info". The intermediate targets "x.xml" and "x.fo" are provided for | |
180 | testing purposes. The other five targets are production targets. For example: | |
181 | ||
182 | make spec.pdf | |
183 | ||
184 | This runs the necessary tools in order to create the file spec.pdf from the | |
9b371988 | 185 | original source spec.xfpt. A number of intermediate files are created during |
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186 | this process, including the master DocBook source, called spec.xml. Of course, |
187 | the usual features of "make" ensure that if this already exists and is | |
188 | up-to-date, it is not needlessly rebuilt. | |
189 | ||
f89d2485 PH |
190 | Because there are now two ways of creating the PostScript and PDF outputs, |
191 | there are two targets for each one. For example fop-spec.ps makes PostScript | |
192 | using fop, and sdop-spec.ps makes it using SDoP. The generic targets spec.ps | |
193 | and spec.pdf now point to the SDoP versions. | |
194 | ||
168e428f | 195 | The "test" series of targets were created so that small tests could easily be |
9b371988 | 196 | run fairly quickly, because processing even the shortish XML document takes |
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197 | a bit of time, and processing the main specification takes ages -- except when |
198 | using SDoP for PostScript and PDF. | |
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199 | |
200 | Another target is "exim.8". This runs a locally written Perl script called | |
201 | x2man, which extracts the list of command line options from the spec.xml file, | |
202 | and creates a man page. There are some XML comments in the spec.xml file to | |
203 | enable the script to find the start and end of the options list. | |
204 | ||
205 | There is also a "clean" target that deletes all the generated files. | |
206 | ||
207 | ||
9b371988 | 208 | CREATING DOCBOOK XML FROM XFPT INPUT |
168e428f | 209 | |
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210 | The small amount of local configuration for xfpt is included at the start of |
211 | the two .xfpt files; there are no separate local xfpt configuration files. | |
212 | Running the xfpt command creates a .xml file from a .xfpt file. When this | |
213 | succeeds, there is no output. | |
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214 | |
215 | ||
216 | DOCBOOK PROCESSING | |
217 | ||
218 | Processing a .xml file into the five different output formats is not entirely | |
219 | straightforward. For a start, the same XML is not suitable for all the | |
220 | different output styles. When the final output is in a text format (.txt, | |
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221 | .texinfo) for instance, all non-ASCII characters in the input must be converted |
222 | to ASCII transliterations because the current processing tools do not do this | |
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223 | correctly automatically. |
224 | ||
225 | In order to cope with these issues in a flexible way, a Perl script called | |
226 | Pre-xml was written. This is used to preprocess the .xml files before they are | |
227 | handed to the main processors. Adding one more tool onto the front of the | |
228 | processing chain does at least seem to be in the spirit of XML processing. | |
229 | ||
f89d2485 PH |
230 | The XML processors other than SDoP make use of style files, which can be |
231 | overridden by local versions. There is one that applies to all styles, called | |
232 | MyStyle.xsl, and others for the different output formats. I have included | |
233 | comments in these style files to explain what changes I have made. Some of the | |
234 | changes are quite significant. | |
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235 | |
236 | ||
237 | THE PRE-XML SCRIPT | |
238 | ||
239 | The Pre-xml script copies a .xml file, making certain changes according to the | |
240 | options it is given. The currently available options are as follows: | |
241 | ||
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242 | -ascii |
243 | ||
595028e4 | 244 | This option is used for ASCII output formats. It makes the following |
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245 | character replacements: |
246 | ||
168e428f | 247 | ’ => ' apostrophe |
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248 | © => (c) copyright |
249 | † => * dagger | |
250 | ‡ => ** double dagger | |
251 | => a space hard space | |
252 | – => - en dash | |
253 | ||
254 | The apostrophe is specified numerically because that is what xfpt generates | |
595028e4 | 255 | from an ASCII single quote character. Non-ASCII characters that are not in |
9b371988 | 256 | this list should not be used without thinking about how they might be |
595028e4 | 257 | converted for the ASCII formats. |
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258 | |
259 | In addition to the character replacements, this option causes quotes to be | |
260 | put round <literal> text items, and <quote> and </quote> to be replaced by | |
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261 | ASCII quote marks. You would think the stylesheet would cope with the latter, |
262 | but it seems to generate non-ASCII characters that w3m then turns into | |
9b371988 | 263 | question marks. |
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264 | |
265 | -bookinfo | |
266 | ||
267 | This option causes the <bookinfo> element to be removed from the XML. It is | |
268 | used for the PostScript/PDF forms of the filter document, in order to avoid | |
269 | the generation of a full title page. | |
270 | ||
271 | -fi | |
272 | ||
273 | Replace any occurrence of "fi" by the ligature fi except when it is | |
274 | inside an XML element, or inside a <literal> part of the text. | |
275 | ||
276 | The use of ligatures would be nice for the PostScript and PDF formats. Sadly, | |
277 | it turns out that fop cannot at present handle the FB01 character correctly. | |
f89d2485 PH |
278 | Happily this problem is now avoided when SDoP is used to generate PostScript |
279 | (and thence PDF) because SDoP automatically uses an "fi" ligature for | |
280 | non-fixed-width fonts. | |
281 | ||
282 | The only xmlto format that handles FB01 is the HTML format, but when I used | |
283 | this in the test version, people complained that it made searching for words | |
284 | difficult. So this option is in practice not used at all. | |
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285 | |
286 | -noindex | |
287 | ||
9b371988 | 288 | Remove the XML to generate a Concept Index and an Options index. The source |
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289 | document has three types of index entry, for variables, options, and concept |
290 | indexes. However, no index is required for the .txt and .texinfo outputs. | |
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291 | |
292 | -oneindex | |
293 | ||
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294 | Remove the XML to generate separate variables, options, and concept indexes, |
295 | and add XML to generate a single index. The only output processors that | |
296 | support multiple indexes are SDoP and the processor that produces "formatted | |
297 | objects" for PostScript and PDF output for fop. The HTML processor ignores | |
298 | the XML settings for multiple indexes and just makes one unified index. | |
299 | Specifying three indexes gets you three copies of the same index, so this has | |
300 | to be changed. | |
168e428f | 301 | |
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302 | -optbreak |
303 | ||
304 | Look for items of the form <option>...</option> and <varname>...</varname> in | |
305 | ordinary paragraphs, and insert ​ after each underscore in the | |
306 | enclosed text. The same is done for any word containing four or more upper | |
307 | case letters (compile-time options in the Exim specification). The character | |
308 | ​ is a zero-width space. This means that the line may be split after | |
309 | one of these underscores, but no hyphen is inserted. | |
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310 | |
311 | ||
312 | CREATING POSTSCRIPT AND PDF | |
313 | ||
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314 | These two output formats are created either by using my new SDoP program to |
315 | produce PostScript which can then be run through ps2pdf to make a PDF, or by | |
316 | using xmlto and fop in the old way. | |
317 | ||
318 | ||
319 | USING SDOP TO CREATE POSTSCRIPT AND PDF | |
320 | ||
321 | PostScript output is created in two stages. First, the XML is pre-processed by | |
322 | the Pre-xml script. For the filter document, the <bookinfo> element is removed | |
323 | so that no title page is generated. For the main specification, the only change | |
324 | is to insert line breakpoints via -optbreak. | |
325 | ||
326 | The SDoP program is then used to create PostScript output directly from the XML | |
327 | input. Then the ps2pdf command is used to generated a PDF from the PostScript. | |
328 | There are no external stylesheets that are used by SDoP. Any variations to the | |
329 | default format are specified inline using "processing instructions". | |
330 | ||
331 | ||
332 | USING XMLTO AND FOP TO CREATE POSTSCRIPT AND PDF | |
333 | ||
334 | This is the original way of creating PostScript and PDF output. The processing | |
335 | happens in three stages, with an additional fourth stage for PDF. First, the | |
336 | XML is pre-processed by the Pre-xml script. For the filter document, the | |
337 | <bookinfo> element is removed so that no title page is generated. For the main | |
338 | specification, the only change is to insert line breakpoints via -optbreak. | |
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339 | |
340 | Second, the xmlto command is used to produce a "formatted objects" (.fo) file. | |
341 | This process uses the following stylesheets: | |
342 | ||
343 | (1) Either MyStyle-filter-fo.xsl or MyStyle-spec-fo.xsl | |
344 | (2) MyStyle-fo.xsl | |
345 | (3) MyStyle.xsl | |
346 | (4) MyTitleStyle.xsl | |
347 | ||
348 | The last of these is not used for the filter document, which does not have a | |
349 | title page. The first three stylesheets were created manually, either by typing | |
350 | directly, or by coping from the standard style sheet and editing. | |
351 | ||
352 | The final stylesheet has to be created from a template document, which is | |
353 | called MyTitlepage.templates.xml. This was copied from the standard styles and | |
354 | modified. The template is processed with xsltproc to produce the stylesheet. | |
355 | All this apparatus is appallingly heavyweight. The processing is also very slow | |
356 | in the case of the specification document. However, there should be no errors. | |
357 | ||
9b371988 PH |
358 | The reference book that saved my life while I was trying to get all this to |
359 | work is "DocBook XSL, The Complete Guide", third edition (2005), by Bob | |
360 | Stayton, published by Sagehill Enterprises. | |
361 | ||
362 | In the third part of the processing, the .fo file that is produced by the xmlto | |
363 | command is processed by the fop command to generate either PostScript or PDF. | |
364 | This is also very slow, and you get a whole slew of errors, of which these are | |
365 | a sample: | |
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366 | |
367 | [ERROR] property - "background-position-horizontal" is not implemented yet. | |
368 | ||
369 | [ERROR] property - "background-position-vertical" is not implemented yet. | |
370 | ||
371 | [INFO] JAI support was not installed (read: not present at build time). | |
372 | Trying to use Jimi instead | |
373 | Error creating background image: Error creating FopImage object (Error | |
374 | creating FopImage object | |
375 | (http://docbook.sourceforge.net/release/images/draft.png) : | |
376 | org.apache.fop.image.JimiImage | |
377 | ||
378 | [WARNING] table-layout=auto is not supported, using fixed! | |
379 | ||
380 | [ERROR] Unknown enumerated value for property 'span': inherit | |
381 | ||
382 | [ERROR] Error in span property value 'inherit': | |
383 | org.apache.fop.fo.expr.PropertyException: No conversion defined | |
384 | ||
385 | [ERROR] Areas pending, text probably lost in lineinclude parts matched in the | |
386 | response by response_pattern by means of numeric variables such as | |
387 | ||
388 | The last one is particularly meaningless gobbledegook. Some of the errors and | |
389 | warnings are repeated many times. Nevertheless, it does eventually produce | |
390 | usable output, though I have a number of issues with it (see a later section of | |
391 | this document). Maybe one day there will be a new release of fop that does | |
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392 | better. In the meantime, I have written my own program for making PostScript |
393 | output -- see the previous section -- because the problems with xmlto/fop were | |
394 | sufficiently annoying. | |
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395 | |
396 | The PDF file that is produced by this process has one problem: the pages, as | |
397 | shown by acroread in its thumbnail display, are numbered sequentially from one | |
398 | to the end. Those numbers do not correspond with the page numbers of the body | |
399 | of the document, which makes finding a page from the index awkward. There is a | |
400 | facility in the PDF format to give pages appropriate "labels", but I cannot | |
401 | find a way of persuading fop to generate these. Fortunately, it is possibly to | |
402 | fix up the PDF to add page labels. I wrote a script called PageLabelPDF which | |
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403 | does this. They are shown correctly by acroread and xpdf, but not by |
404 | GhostScript (gv). | |
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405 | |
406 | ||
407 | THE PAGELABELPDF SCRIPT | |
408 | ||
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409 | This script reads the standard input and writes the standard output. It is used |
410 | to "tidy up" the PDF output that is produced by fop. It is not needed when | |
411 | PDF output is generated from SDoP's output using ps2pdf. | |
412 | ||
413 | The PageLabelPDF script searches for the PDF object that sets data in its | |
414 | "Catalog", and adds appropriate information about page labels. The number of | |
415 | front-matter pages (those before chapter 1) is hard-wired into this script as | |
416 | 12 because I could not find a way of determining it automatically. As the | |
417 | current table of contents finishes near the top of the 11th page, there is | |
418 | plenty of room for expansion, so it is unlikely to be a problem. | |
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419 | |
420 | Having added data to the PDF file, the script then finds the xref table at the | |
421 | end of the file, and adjusts its entries to allow for the added text. This | |
422 | simple processing seems to be enough to generate a new, valid, PDF file. | |
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423 | |
424 | ||
425 | CREATING HTML | |
426 | ||
427 | Only two stages are needed to produce HTML, but the main specification is | |
9b371988 | 428 | subsequently postprocessed. The Pre-xml script is called with the -optbreak and |
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429 | -oneindex options to preprocess the XML. Then the xmlto command creates the |
430 | HTML output directly. For the specification document, a directory of files is | |
431 | created, whereas the filter document is output as a single HTML page. The | |
432 | following stylesheets are used: | |
433 | ||
434 | (1) Either MyStyle-chunk-html.xsl or MyStyle-nochunk-html.xsl | |
435 | (2) MyStyle-html.xsl | |
436 | (3) MyStyle.xsl | |
437 | ||
9b371988 | 438 | The first stylesheet references the chunking or non-chunking standard DocBook |
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439 | stylesheet, as appropriate. |
440 | ||
9b371988 PH |
441 | You may see a number of these errors when creating HTML: "Revisionflag on |
442 | unexpected element: literallayout (Assuming block)". They seem to be harmless; | |
443 | the output appears to be what is intended. | |
444 | ||
168e428f PH |
445 | The original HTML that I produced from the SGCAL input had hyperlinks back from |
446 | chapter and section titles to the table of contents. These links are not | |
447 | generated by xmlto. One of the testers pointed out that the lack of these | |
448 | links, or simple self-referencing links for titles, makes it harder to copy a | |
449 | link name into, for example, a mailing list response. | |
450 | ||
451 | I could not find where to fiddle with the stylesheets to make such a change, if | |
452 | indeed the stylesheets are capable of it. Instead, I wrote a Perl script called | |
453 | TidyHTML-spec to do the job for the specification document. It updates the | |
454 | index.html file (which contains the the table of contents) setting up anchors, | |
455 | and then updates all the chapter files to insert appropriate links. | |
456 | ||
457 | The index.html file as built by xmlto contains the whole table of contents in a | |
458 | single line, which makes is hard to debug by hand. Since I was postprocessing | |
459 | it anyway, I arranged to insert newlines after every '>' character. | |
460 | ||
068aaea8 PH |
461 | The TidyHTML-spec script also processes every HTML file, to tidy up some of the |
462 | untidy features therein. It turns <div class="literallayout"><p> into <div | |
463 | class="literallayout"> and a matching </p></div> into </div> to get rid of | |
464 | unwanted vertical white space in literallayout blocks. Before each occurrence | |
465 | of </td> it inserts so that the table's cell is a little bit wider than | |
466 | the text itself. | |
467 | ||
168e428f | 468 | The TidyHTML-spec script also takes the opportunity to postprocess the |
4f578862 | 469 | spec_html/ix01.html file, which contains the document index. Again, the index |
168e428f PH |
470 | is generated as one single line, so it splits it up. Then it creates a list of |
471 | letters at the top of the index and hyperlinks them both ways from the | |
472 | different letter portions of the index. | |
473 | ||
474 | People wanted similar postprocessing for the filter.html file, so that is now | |
475 | done using a similar script called TidyHTML-filter. It was easier to use a | |
476 | separate script because filter.html is a single file rather than a directory, | |
477 | so the logic is somewhat different. | |
478 | ||
479 | ||
480 | CREATING TEXT FILES | |
481 | ||
9b371988 | 482 | This happens in four stages. The Pre-xml script is called with the -ascii, |
595028e4 | 483 | -optbreak, and -noindex options to convert the input to ASCII characters, |
9b371988 PH |
484 | insert line break points, and disable the production of an index. Then the |
485 | xmlto command converts the XML to a single HTML document, using these | |
486 | stylesheets: | |
168e428f PH |
487 | |
488 | (1) MyStyle-txt-html.xsl | |
489 | (2) MyStyle-html.xsl | |
490 | (3) MyStyle.xsl | |
491 | ||
492 | The MyStyle-txt-html.xsl stylesheet is the same as MyStyle-nochunk-html.xsl, | |
493 | except that it contains an addition item to ensure that a generated "copyright" | |
494 | symbol is output as "(c)" rather than the Unicode character. This is necessary | |
495 | because the stylesheet itself generates a copyright symbol as part of the | |
496 | document title; the character is not in the original input. | |
497 | ||
595028e4 | 498 | The w3m command is used with the -dump option to turn the HTML file into ASCII |
168e428f | 499 | text, but this contains multiple sequences of blank lines that make it look |
9b371988 PH |
500 | awkward. Furthermore, chapter and section titles do not stand out very well. A |
501 | local Perl script called Tidytxt is used to post-process the output. First, it | |
502 | converts sequences of blank lines into a single blank lines. Then it searches | |
503 | for chapter and section headings. Each chapter heading is uppercased, and | |
504 | preceded by an extra two blank lines and a line of equals characters. An extra | |
505 | newline is inserted before each section heading, and they are underlined with | |
506 | hyphens. | |
168e428f | 507 | |
01496481 TF |
508 | The output of xmlto also contains non-ASCII Unicode characters that w3m passes |
509 | through. Fortunately, they are few, and Tidytxt cleans them up as well. Some | |
510 | headings use "box drawing" characters in the range U+2500 to U+253F which are | |
511 | translated into -+| as appropriate, and U+00A0 (hard space) and U+25CF (bullet) | |
512 | are translated into plain spaces and asterisks. (It might be possible to do all | |
513 | this in the same way as I dealt with copyright - see above - but adding a few | |
514 | lines of Perl to an existing script was a lot easier.) | |
595028e4 | 515 | |
168e428f PH |
516 | |
517 | CREATING INFO FILES | |
518 | ||
9b371988 PH |
519 | This process starts with the same Pre-xml call as for text files. Non-ascii |
520 | characters in the source are transliterated, and the <index> elements are | |
521 | removed. The docbook2texi script is then called to convert the XML file into a | |
522 | Texinfo file. However, this is not quite enough. The converted file ends up | |
523 | with "conceptindex" and "optionindex" items, which are not recognized by the | |
4f578862 PH |
524 | makeinfo command. These have to be changed to "cindex" and "findex" |
525 | respectively in the final .texinfo file. Furthermore, the main menu lacks a | |
526 | pointer to the index, and indeed the index node itself is missing. These | |
527 | problems are fixed by running the file through a script called TidyInfo. | |
e492cc8d | 528 | Finally, a call of makeinfo creates a .info file. |
168e428f PH |
529 | |
530 | There is one apparently unconfigurable feature of docbook2texi: it does not | |
531 | seem possible to give it a file name for its output. It chooses a name based on | |
532 | the title of the document. Thus, the main specification ends up in a file | |
533 | called the_exim_mta.texi and the filter document in exim_filtering.texi. These | |
534 | files are removed after their contents have been copied and modified by the | |
4f578862 | 535 | TidyInfo script, which writes to a .texinfo file. |
168e428f PH |
536 | |
537 | ||
538 | CREATING THE MAN PAGE | |
539 | ||
540 | I wrote a Perl script called x2man to create the exim.8 man page from the | |
9b371988 | 541 | DocBook XML source. I deliberately did NOT start from the xfpt source, |
168e428f PH |
542 | because it is the DocBook source that is the "standard". This comment line in |
543 | the DocBook source marks the start of the command line options: | |
544 | ||
545 | <!-- === Start of command line options === --> | |
546 | ||
547 | A similar line marks the end. If at some time in the future another way other | |
9b371988 | 548 | than xfpt is used to maintain the DocBook source, it needs to be capable of |
168e428f PH |
549 | maintaining these comments. |
550 | ||
551 | ||
552 | UNRESOLVED PROBLEMS | |
553 | ||
554 | There are a number of unresolved problems with producing the Exim documentation | |
555 | in the manner described above. I will describe them here in the hope that in | |
f89d2485 PH |
556 | future some way round them can be found. Some of the problems are solved by |
557 | using SDoP instead of xmlto/fop to produce PostScript and PDF output. | |
168e428f | 558 | |
9b371988 PH |
559 | (1) When a whole chain of tools is processing a file, an error somewhere |
560 | in the middle is often very hard to debug. For instance, an error in the | |
561 | xfpt file might not show up until an XML processor throws a wobbly because | |
168e428f PH |
562 | the generated XML is bad. You have to be able to read XML and figure out |
563 | what generated what. One of the reasons for creating the "test" series of | |
564 | targets was to help in checking out these kinds of problem. | |
565 | ||
566 | (2) There is a mechanism in XML for marking parts of the document as | |
f89d2485 PH |
567 | "revised", and I have arranged for xfpt markup to use it. However, the |
568 | only xmlto output format that pays attention to this is the HTML output, | |
569 | which sets a green background. If xmlto/fop is used to generate PostScript | |
570 | and PDF, there are no revision marks (change bars). This problem | |
571 | is not present when SDoP is used. However, the text and Texinfo output | |
572 | format lack revision indications. | |
168e428f PH |
573 | |
574 | (3) The index entries in the HTML format take you to the top of the section | |
575 | that is referenced, instead of to the point in the section where the index | |
576 | marker was set. | |
577 | ||
e492cc8d PH |
578 | (4) The HTML output supports only a single index, so the variable, options, |
579 | and concept index entries have to be merged. | |
168e428f | 580 | |
f89d2485 PH |
581 | (5) The index for the PostScript/PDF output created by xmlto/fop does not |
582 | merge identical page numbers, which makes some entries look ugly. This is | |
583 | not a problem when SDoP is used. | |
168e428f | 584 | |
e492cc8d PH |
585 | (6) The HTML index and the PostScript/PDF indexes, when made with xmlto/fop, |
586 | make no use of textual markup; the text is all roman, without any italic | |
587 | or boldface. For PostScript/PDF, this is not a problem when SDoP is used. | |
168e428f | 588 | |
f89d2485 PH |
589 | (7) I turned off hyphenation in the PostScript/PDF output produced by |
590 | xmlto/fop, because it was being done so badly. Needless to say, I made | |
591 | SDoP do a better job. These comments apply to xmlto/fop: | |
168e428f PH |
592 | |
593 | (a) It seems to force hyphenation if it is at all possible, without | |
594 | regard to the "tightness" or "looseness" of the line. Decent | |
595 | formatting software should attempt hyphenation only if the line is | |
596 | over some "looseness" threshold; otherwise you get far too many | |
597 | hyphenations, often for several lines in succession. | |
598 | ||
599 | (b) It uses an algorithmic form of hyphenation that doesn't always produce | |
e492cc8d PH |
600 | acceptable word breaks. (I prefer to use a hyphenation dictionary, |
601 | which is what SDoP does.) | |
168e428f | 602 | |
f89d2485 | 603 | (8) The PostScript/PDF output produced by xmlto/fop is badly paginated: |
168e428f PH |
604 | |
605 | (a) There seems to be no attempt to avoid "widow" and "orphan" lines on | |
606 | pages. A "widow" is the last line of a paragraph at the top of a page, | |
607 | and an "orphan" is the first line of a paragraph at the bottom of a | |
608 | page. | |
609 | ||
610 | (b) There seems to be no attempt to prevent section headings being placed | |
611 | last on a page, with no following text on the page. | |
612 | ||
f89d2485 PH |
613 | Neither of these problems occurs when SDoP is used to produce the |
614 | PostScript/PDF output. | |
615 | ||
168e428f | 616 | (9) The fop processor does not support "fi" ligatures, not even if you put the |
f89d2485 PH |
617 | appropriate Unicode character into the source by hand. Again, this is not |
618 | a problem if SDoP is used. | |
168e428f | 619 | |
9b371988 PH |
620 | (10) There are no diagrams in the new documentation. This is something I hope |
621 | to work on. The previously used Aspic command for creating line art from a | |
168e428f PH |
622 | textual description can output Encapsulated PostScript or Scalar Vector |
623 | Graphics, which are two standard diagram representations. Aspic could be | |
624 | formally released and used to generate output that could be included in at | |
625 | least some of the output formats. | |
626 | ||
9b371988 PH |
627 | (11) The use of a "zero-width space" works well as a way of specifying that |
628 | Exim option names can be split, without hyphens, over line breaks. | |
9b371988 | 629 | |
f89d2485 PH |
630 | However, when xmlto/fop is being used and an option is not split, if the |
631 | line is very "loose", the zero-width space is expanded, along with other | |
632 | spaces. This is a totally crazy thing to, but unfortunately it is | |
633 | suggested by the Unicode definition of the zero-width space, which says | |
634 | "its presence between two characters does not prevent increased letter | |
635 | spacing in justification". It seems that the implementors of fop have | |
636 | understood "letter spacing" also to include "word spacing". Sigh. | |
637 | ||
638 | This problem does not arise when SDoP is used. | |
639 | ||
640 | The consequence of (7), (8), and (9) is that the PostScript/PDF output as | |
641 | produced by xmlto/fop looks as if it comes from some of the very early attempts | |
642 | at text formatting of around 20 years ago. We can only hope that 20 years' | |
643 | progress is not going to get lost, and that things will improve in this area. | |
644 | My small contribution to this has been to write SDoP, which, though simple and | |
645 | "non-standard", does get some of these formatting issues right. | |
168e428f PH |
646 | |
647 | ||
648 | LIST OF FILES | |
649 | ||
9b371988 | 650 | Markup.txt Describes the xfpt markup that is used |
168e428f PH |
651 | HowItWorks.txt This document |
652 | Makefile The makefile | |
168e428f PH |
653 | MyStyle-chunk-html.xsl Stylesheet for chunked HTML output |
654 | MyStyle-filter-fo.xsl Stylesheet for filter fo output | |
655 | MyStyle-fo.xsl Stylesheet for any fo output | |
656 | MyStyle-html.xsl Stylesheet for any HTML output | |
657 | MyStyle-nochunk-html.xsl Stylesheet for non-chunked HTML output | |
658 | MyStyle-spec-fo.xsl Stylesheet for spec fo output | |
659 | MyStyle-txt-html.xsl Stylesheet for HTML=>text output | |
660 | MyStyle.xsl Stylesheet for all output | |
661 | MyTitleStyle.xsl Stylesheet for spec title page | |
662 | MyTitlepage.templates.xml Template for creating MyTitleStyle.xsl | |
663 | Myhtml.css Experimental css stylesheet for HTML output | |
f89d2485 | 664 | PageLabelPDF Script to postprocess xmlto/fop PDF output |
168e428f PH |
665 | Pre-xml Script to preprocess XML |
666 | TidyHTML-filter Script to tidy up the filter HTML output | |
667 | TidyHTML-spec Script to tidy up the spec HTML output | |
4f578862 | 668 | TidyInfo Script to sort index problems in Texinfo output |
168e428f | 669 | Tidytxt Script to compact multiple blank lines |
9b371988 PH |
670 | filter.xfpt xfpt source of the filter document |
671 | spec.xfpt xfpt source of the specification document | |
168e428f PH |
672 | x2man Script to make the Exim man page from the XML |
673 | ||
168e428f PH |
674 | |
675 | Philip Hazel | |
e492cc8d | 676 | Last updated: 31 August 2007 |