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11 <h1 align="center">The XSLT C library for Gnome</h1>
13 <h1 style="text-align: center">libxslt</h1>
15 <p>Libxslt is the <a href="http://www.w3.org/TR/xslt">XSLT</a> C library
16 developed for the Gnome project. XSLT itself is a an XML language to define
17 transformation for XML. Libxslt is based on <a
18 href="http://xmlsoft.org/">libxml2</a> the XML C library developed for the
19 Gnome project. It also implements most of the <a
20 href="http://www.exslt.org/">EXSLT</a> set of processor-portable extensions
21 functions and some of Saxon's evaluate and expressions extensions.</p>
23 <p>People can either embed the library in their application or use xsltproc
24 the command line processing tool. This library is free software and can be
25 reused in commercial applications (see the <a href="intro.html">intro</a>)</p>
27 <p>External documents:</p>
29 <li>John Fleck wrote <a href="tutorial/libxslttutorial.html">a tutorial for
31 <li><a href="xsltproc.html">xsltproc user manual</a></li>
32 <li><a href="http://xmlsoft.org/">the libxml documentation</a></li>
37 <p>Logo designed by <a href="mailto:liyanage@access.ch">Marc Liyanage</a>.</p>
39 <h2><a name="Introducti">Introduction</a></h2>
41 <p>This document describes <a href="http://xmlsoft.org/XSLT/">libxslt</a>,
42 the <a href="http://www.w3.org/TR/xslt">XSLT</a> C library developed for the
43 <a href="http://www.gnome.org/">Gnome</a> project.</p>
45 <p>Here are some key points about libxslt:</p>
47 <li>Libxslt is a C implementation</li>
48 <li>Libxslt is based on libxml for XML parsing, tree manipulation and XPath
50 <li>It is written in plain C, making as few assumptions as possible, and
51 sticking closely to ANSI C/POSIX for easy embedding. Should works on
52 Linux/Unix/Windows.</li>
53 <li>This library is released under the <a
54 href="http://www.opensource.org/licenses/mit-license.html">MIT
56 <li>Though not designed primarily with performances in mind, libxslt seems
57 to be a relatively fast processor.</li>
60 <h2><a name="Documentat">Documentation</a></h2>
62 <p>There are some on-line resources about using libxslt:</p>
64 <li>Check the <a href="html/libxslt-lib.html#LIBXSLT-LIB">API
65 documentation</a> automatically extracted from code comments.</li>
66 <li>Look at the <a href="http://mail.gnome.org/archives/xslt/">mailing-list
68 <li>Of course since libxslt is based on libxml, it's a good idea to at
69 least read <a href="http://xmlsoft.org/">libxml description</a></li>
72 <h2><a name="Reporting">Reporting bugs and getting help</a></h2>
74 <p>If you need help with the XSLT language itself, here are a number of
77 <li>I strongly suggest to subscribe to <a
78 href="http://www.mulberrytech.com/xsl/xsl-list">XSL-list</a>, check <a
79 href="http://www.biglist.com/lists/xsl-list/archives/">the XSL-list
81 <li>The <a href="http://www.dpawson.co.uk/xsl/xslfaq.html">XSL FAQ</a>.</li>
83 href="http://www.nwalsh.com/docs/tutorials/xsl/xsl/slides.html">tutorial</a>
84 written by Paul Grosso and Norman Walsh is a very good on-line
85 introdution to the language.</li>
87 href="http://www.zvon.org/xxl/XSLTutorial/Books/Book1/index.html">only
88 Zvon XSLT tutorial</a> details a lot of constructs with examples.</li>
89 <li><a href="http://www.jenitennison.com/xslt/index.html">Jeni Tennison's
90 XSLT</a> pages provide links to a lot of answers</li>
91 <li>the <a href="http://incrementaldevelopment.com/xsltrick/">Gallery of
92 XSLT Tricks</a> provides non-standard use case of XSLT</li>
93 <li>And I suggest to buy Michael Kay "XSLT Programmer's Reference" book
94 published by <a href="http://www.wrox.com/">Wrox</a> if you plan to work
95 seriously with XSLT in the future.</li>
98 <p>Well, bugs or missing features are always possible, and I will make a
99 point of fixing them in a timely fashion. The best way to report a bug is to
100 use the <a href="http://bugzilla.gnome.org/buglist.cgi?product=libxslt">Gnome
101 bug tracking database</a> (make sure to use the "libxslt" module name). I
102 look at reports there regularly and it's good to have a reminder when a bug
103 is still open. Be sure to specify that the bug is for the package libxslt.</p>
105 <p>For small problems you can try to get help on IRC, the #xml channel on
106 irc.gnome.org (port 6667) usually have a few person subscribed which may help
107 (but there is no garantee and if a real issue is raised it should go on the
108 mailing-list for archival).</p>
110 <p>There is also a mailing-list <a
111 href="mailto:xslt@gnome.org">xslt@gnome.org</a> for libxslt, with an <a
112 href="http://mail.gnome.org/archives/xslt/">on-line archive</a>. To subscribe
113 to this list, please visit the <a
114 href="http://mail.gnome.org/mailman/listinfo/xslt">associated Web</a> page
115 and follow the instructions.</p>
117 <p>Alternatively, you can just send the bug to the <a
118 href="mailto:xslt@gnome.org">xslt@gnome.org</a> list, if it's really libxslt
119 related I will approve it.. Please do not send me mail directly especially
120 for portability problem, it makes things really harder to track and in some
121 cases I'm not the best person to answer a given question, ask the list
122 instead. <strong>Do not send code, I won't debug it</strong> (but patches are
123 really appreciated!).</p>
125 <p>Check the following too <span style="color: #E50000">before
128 <li><a href="search.php">use the search engine</a> to get informations
129 related to your problem.</li>
130 <li>make sure you are <a href="ftp://xmlsoft.org/">using a recent
131 version</a>, and that the problem still shows up in those</li>
132 <li>check the <a href="http://mail.gnome.org/archives/xslt/">list
133 archives</a> to see if the problem was reported already, in this case
134 there is probably a fix available, similarly check the <a
135 href="http://bugzilla.gnome.org/buglist.cgi?product=libxslt">registered
137 <li>make sure you can reproduce the bug with xsltproc, a very useful thing
138 to do is run the transformation with -v argument and redirect the
139 standard error to a file, then search in this file for the transformation
140 logs just preceding the possible problem</li>
141 <li>Please send the command showing the error as well as the input and
142 stylesheet (as an attachment)</li>
145 <p>Then send the bug with associated informations to reproduce it to the <a
146 href="mailto:xslt@gnome.org">xslt@gnome.org</a> list; if it's really libxslt
147 related I will approve it. Please do not send mail to me directly, it makes
148 things really hard to track and in some cases I am not the best person to
149 answer a given question, ask on the list.</p>
151 <p>To <span style="color: #E50000">be really clear about support</span>:</p>
153 <li>Support or help <span style="color: #E50000">request MUST be sent to
154 the list or on bugzilla</span> in case of problems, so that the Question
155 and Answers can be shared publicly. Failing to do so carries the implicit
156 message "I want free support but I don't want to share the benefits with
157 others" and is not welcome. I will automatically Carbon-Copy the
158 xslt@gnome.org mailing list for any technical reply made about libxml2 or
160 <li>There is <span style="color: #E50000">no garantee for support</span>,
161 if your question remains unanswered after a week, repost it, making sure
162 you gave all the detail needed and the informations requested.</li>
163 <li>Failing to provide informations as requested or double checking first
164 for prior feedback also carries the implicit message "the time of the
165 library maintainers is less valuable than my time" and might not be
169 <p>Of course, bugs reports with a suggested patch for fixing them will
170 probably be processed faster.</p>
172 <p>If you're looking for help, a quick look at <a
173 href="http://mail.gnome.org/archives/xslt/">the list archive</a> may actually
174 provide the answer, I usually send source samples when answering libxslt
175 usage questions. The <a
176 href="html/libxslt-lib.html#LIBXSLT-LIB">auto-generated documentation</a> is
177 not as polished as I would like (I need to learn more about Docbook), but
178 it's a good starting point.</p>
180 <h2><a name="help">How to help</a></h2>
182 <p>You can help the project in various ways, the best thing to do first is to
183 subscribe to the mailing-list as explained before, check the <a
184 href="http://mail.gnome.org/archives/xslt/">archives </a>and the <a
185 href="http://bugzilla.gnome.org/buglist.cgi?product=libxslt">Gnome bug
188 <li>provide patches when you find problems</li>
189 <li>provide the diffs when you port libxslt to a new platform. They may not
190 be integrated in all cases but help pinpointing portability problems
192 <li>provide documentation fixes (either as patches to the code comments or
194 <li>provide new documentations pieces (translations, examples, etc ...)</li>
195 <li>Check the TODO file and try to close one of the items</li>
196 <li>take one of the points raised in the archive or the bug database and
197 provide a fix. <a href="mailto:daniel@veillard.com">Get in touch with me
198 </a>before to avoid synchronization problems and check that the suggested
199 fix will fit in nicely :-)</li>
202 <h2><a name="Downloads">Downloads</a></h2>
204 <p>The latest versions of libxslt can be found on <a
205 href="ftp://xmlsoft.org/">xmlsoft.org</a> (<a
206 href="ftp://speakeasy.rpmfind.net/pub/libxml/">Seattle</a>, <a
207 href="ftp://fr.rpmfind.net/pub/libxml/">France</a>) or on the <a
208 href="ftp://ftp.gnome.org/pub/GNOME/MIRRORS.html">Gnome FTP server</a> as a
209 <a href="ftp://ftp.gnome.org/pub/GNOME/sources/libxslt/1.1/">source
210 archive</a>, Antonin Sprinzl also provides <a
211 href="ftp://gd.tuwien.ac.at/pub/libxml/">a mirror in Austria</a>. (NOTE that
212 you need the <a href="http://rpmfind.net/linux/RPM/libxml2.html">libxml2</a>,
213 <a href="http://rpmfind.net/linux/RPM/libxml2-devel.html">libxml2-devel</a>,
214 <a href="http://rpmfind.net/linux/RPM/libxslt.html">libxslt</a> and <a
215 href="http://rpmfind.net/linux/RPM/libxslt-devel.html">libxslt-devel</a>
216 packages installed to compile applications using libxslt.) <a
217 href="mailto:igor@zlatkovic.com">Igor Zlatkovic</a> is now the maintainer of
219 href="http://www.zlatkovic.com/projects/libxml/index.html">he provides
220 binaries</a>. <a href="mailto:Gary.Pennington@sun.com">Gary Pennington</a>
221 provides <a href="http://garypennington.net/libxml2/">Solaris binaries</a>.
222 <a href="mailto:Steve.Ball@zveno.com">Steve Ball</a> provides <a
223 href="http://www.zveno.com/open_source/libxml2xslt.html">Mac Os X
226 <p><a name="Contribs">Contribs:</a></p>
228 <p>I do accept external contributions, especially if compiling on another
229 platform, get in touch with me to upload the package. I will keep them in the
230 <a href="ftp://xmlsoft.org/contribs/">contrib directory</a></p>
232 <p>Libxslt is also available from CVS:</p>
235 href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&dir=libxslt">Gnome
236 CVS base</a>. Check the <a
237 href="http://developer.gnome.org/tools/cvs.html">Gnome CVS Tools</a>
238 page; the CVS module is <b>libxslt</b>.</p>
240 <li><a href="ftp://xmlsoft.org/XSLT/cvs-snapshot.tar.gz">daily snapshots
241 from CVS</a> are also provided</li>
244 <h2><a name="FAQ">FAQ</a></h2>
246 <li><em>Troubles compiling or linking programs using libxslt</em>
247 <p>Usually the problem comes from the fact that the compiler doesn't get
248 the right compilation or linking flags. There is a small shell script
249 <code>xslt-config</code> which is installed as part of libxslt usual
250 install process which provides those flags. Use</p>
251 <p><code>xslt-config --cflags</code></p>
252 <p>to get the compilation flags and</p>
253 <p><code>xslt-config --libs</code></p>
254 <p>to get the linker flags. Usually this is done directly from the
256 <p><code>CFLAGS=`xslt-config --cflags`</code></p>
257 <p><code>LIBS=`xslt-config --libs`</code></p>
258 <p>Note also that if you use the EXSLT extensions from the program then
259 you should prepend <code>-lexslt</code> to the LIBS options</p>
261 <li><em>passing parameters on the xsltproc command line doesn't work</em>
262 <p><em>xsltproc --param test alpha foo.xsl foo.xml</em></p>
263 <p><em>the param does not get passed and ends up as ""</em></p>
264 <p>In a nutshell do a double escaping at the shell prompt:</p>
265 <p>xsltproc --param test "'alpha'" foo.xsl foo.xml</p>
266 <p>i.e. the string value is surrounded by " and ' then terminated by '
267 and ". Libxslt interpret the parameter values as XPath expressions, so
268 the string -><code>alpha</code><- is intepreted as the node set
269 matching this string. You really want -><code>'alpha'</code><- to
270 be passed to the processor. And to allow this you need to escape the
271 quotes at the shell level using -><code>"'alpha'"</code><- .</p>
273 <p>xsltproc --stringparam test alpha foo.xsl foo.xml</p>
275 <li><em>Is there C++ bindings ?</em>
276 <p>Yes for example <a
277 href="http://pmade.org/pjones/software/xmlwrapp/">xmlwrapp</a> , see <a
278 href="python.html">the related pages about bindings</a></p>
282 <h2><a name="News">News</a></h2>
284 <h3>CVS only : check the <a
285 href="http://cvs.gnome.org/lxr/source/libxslt/ChangeLog">Changelog</a> file
286 for a really accurate description</h3>
288 <h3>1.1.1: Dec 10 2003</h3>
290 <li>code cleanup (William Brack)</li>
291 <li>Windows: Makefile improvements (Igor Zlatkovic)</li>
292 <li>documentation improvements: William Brack, libexslt man page (Jonathan
294 <li>param in EXSLT functions (Shaun McCance)</li>
295 <li>XSLT debugging improvements (Mark Vakoc)</li>
296 <li>bug fixes: number formatting (Bjorn Reese), exslt:tokenize (William
297 Brack), key selector parsing with | reported by Oleg Paraschenko,
298 xsl:element with computed namespaces (William Brack), xslt:import/include
299 recursion detection (William Brack), exslt:function used in keys (William
300 Brack), bug when CDATA_SECTION are foun in the tree (William Brack),
301 entities handling when using XInclude.</li>
304 <h3>1.1.0: Nov 4 2003</h3>
306 <li>Removed DocBook SGML broken support</li>
307 <li>fix xsl:key to work with PIs</li>
308 <li>Makefile and build improvement (Graham Wilson), build cleanup (William
309 Brack), macro fix (Justin Fletcher), build outside of source tree (Roumen
311 <li>xsltproc option display fix (Alexey Efimov), --load-trace (Crutcher
313 <li>Python: never use stdout for error</li>
314 <li>extension memory error fix (Karl Eichwalder)</li>
315 <li>header path fixes (Steve Ball)</li>
316 <li>added saxon:line-number() to libexslt (Brett Kail)</li>
317 <li>Fix some tortuous template problems when using predicates (William
319 <li>Debugger status patch (Kasimier Buchcik)</li>
320 <li>Use new libxml2-2.6.x APIs for faster processing</li>
321 <li>Make sure xsl:sort is empty</li>
322 <li>Fixed a bug in default processing of attributes</li>
323 <li>Removes the deprecated breakpoint library</li>
324 <li>detect invalid names on templates (William Brack)</li>
325 <li>fix exslt:document (and similar) base handling problem</li>
328 <h3>1.0.33: Sep 12 2003</h3>
330 <p>This is a bugfix only release</p>
332 <li>error message missing argument (William Brack)</li>
333 <li>mode not cascaded in template fallbacks (William Brack)</li>
334 <li>catch redefinition of parameter/variables (William Brack)</li>
335 <li>multiple keys with same namespace name (William Brack)</li>
336 <li>patch for compilation using MingW on Windows (Mikhail Grushinskiy)</li>
337 <li>header export macros for Windows (Igor Zlatkovic)</li>
338 <li>cdata-section-elements handling of namespaced names</li>
339 <li>compilation without libxml2 XPointer support (Mark Vadoc)</li>
340 <li>apply-templates crash (William Brack)</li>
341 <li>bug with imported templates (William Brack)</li>
342 <li>imported attribute-sets merging bug (DocBook) (William Brack)</li>
345 <h3>1.0.32: Aug 9 2003</h3>
347 <li>bugfixes: xsltSaveResultToFile() python binding (Chris Jaeger), EXSLT
348 function (William Brack), RVT for globals (William Brack), EXSLT date
350 <p>speed of large text output, xsl:copy with attributes, strip-space and
351 namespaces prefix, fix for --path xsltproc option, EXST:tokenize (Shaun
352 McCance), EXSLT:seconds (William Brack), sort with multiple keys (William
353 Brack), checking of { and } for attribute value templates (William
356 <li>Python bindings for extension elements (Sean Treadway)</li>
357 <li>EXSLT:split added (Shaun McCance)</li>
358 <li>portability fixes for HP-UX/Solaris/IRIX (William Brack)</li>
362 <h3>1.0.31: Jul 6 2003</h3>
364 <li>bugfixes: xsl:copy on namespace nodes, AVT for xsl:sort order, fix for
365 the debugger (Keith Isdale), output filename limitation, trio.h and
366 triodef.h added (Albert Chin), EXSLT node-set (Peter Breitenlohner),
367 xsltChoose and whitespace (Igor Zlatkovic),
368 <p>stylesheet compilation (Igor Zlatkovic), NaN and sort (William Brack),
369 RVT bug introduced in 1.0.30</p>
371 <li>avoid generating &quot; (fix in libxml2-2.5.8)</li>
372 <li>fix 64bit cleaness problem and compilation troubles introduced in
374 <li>Windows makefile generation (Igor Zlatkovic)</li>
375 <li>HP-UX portability fix</li>
378 <h3>1.0.30: May 4 2003</h3>
380 <li>Fixes and new APIs to handle Result Value Trees and avoid leaks</li>
381 <li>Fixes for: EXSLT math pow() function (Charles Bozeman), global
382 parameter and global variables mismatch, a segfault on pattern
383 compilation errors, namespace copy in xsl:copy-of, python generator
384 problem, OpenVMS trio update, premature call to xsltFreeStackElem (Igor),
385 current node when templates applies to attributes</li>
388 <h3>1.0.29: Apr 1 2003</h3>
390 <li>performance improvements especially for large flat documents</li>
391 <li>bug fixes: Result Value Tree handling, XML IDs, keys(), extra namespace
392 declarations with xsl:elements.</li>
393 <li>portability: python and trio fixes (Albert Chin), python on Solaris
397 <h3>1.0.28: Mar 24 2003</h3>
399 <li>fixed node() in patterns semantic.</li>
400 <li>fixed a memory access problem in format-number()</li>
401 <li>fixed stack overflow in recursive global variable or params</li>
402 <li>cleaned up Result Value Tree handling, and fixed a couple of old bugs
406 <h3>1.0.27: Feb 24 2003</h3>
408 <li>bug fixes: spurious xmlns:nsX="" generation, serialization bug (in
409 libxml2), a namespace copy problem, errors in the RPM spec prereqs</li>
410 <li>Windows path canonicalization and document cache fix (Igor)</li>
413 <h3>1.0.26: Feb 10 2003</h3>
415 <li>Fixed 3 serious bugs in document() and stylesheet compilation which
416 could lead to a crash</li>
419 <h3>1.0.25: Feb 5 2003</h3>
421 <li>Bug fix: double-free for standalone stylesheets introduced in 1.0.24, C
422 syntax pbm, 3 bugs reported by Eric van der Vlist</li>
423 <li>Some XPath and XInclude related problems were actually fixed in
425 <li>Documentation: emphasize taht --docbook is not for XML docs.</li>
428 <h3>1.0.24: Jan 14 2003</h3>
430 <li>bug fixes: imported global varables, python bindings (Stéphane Bidoul),
431 EXSLT memory leak (Charles Bozeman), namespace generation on
432 xsl:attribute, space handling with imports (Daniel Stodden),
433 extension-element-prefixes (Josh Parsons), comments within xsl:text (Matt
434 Sergeant), superfluous xmlns generation, XInclude related bug for
435 numbering, EXSLT strings (Alexey Efimov), attribute-sets computation on
436 imports, extension module init and shutdown callbacks not called</li>
437 <li>HP-UX portability (Alexey Efimov), Windows makefiles (Igor and Stephane
438 Bidoul), VMS makefile updates (Craig A. Berry)</li>
439 <li>adds xsltGetProfileInformation() (Michael Rothwell)</li>
440 <li>fix the API generation scripts</li>
441 <li>API to provide the sorting routines (Richard Jinks)</li>
442 <li>added XML description of the EXSLT API</li>
443 <li>added ESXLT URI (un)escaping (Jörg Walter)</li>
444 <li>Some memory leaks have been found and fixed</li>
445 <li>document() now support fragment identifiers in URIs</li>
448 <h3>1.0.23: Nov 17 2002</h3>
450 <li>Windows build cleanup (Igor)</li>
451 <li>Unix build and RPM packaging cleanup</li>
452 <li>Improvement of the python bindings: extension functions and activating
454 <li>various bug fixes: number formatting, portability for bounded string
455 functions, CData nodes, key(), @*[...] patterns</li>
456 <li>Documentation improvements (John Fleck)</li>
457 <li>added libxslt.m4 (Thomas Schraitle)</li>
460 <h3>1.0.22: Oct 18 2002</h3>
462 <li>Updates on the Windows Makefiles</li>
463 <li>Added a security module, and a related set of new options to
465 <li>Allowed per transformation error handler.</li>
466 <li>Fixed a few bugs: node() semantic, URI escaping, media-type, attribute
470 <h3>1.0.21: Sep 26 2002</h3>
472 <li>Bug fixes: match="node()", date:difference() (Igor and Charlie
473 Bozeman), disable-output-escaping</li>
474 <li>Python bindings: style.saveResultToString() from Ralf Mattes</li>
475 <li>Logos from Marc Liyanage</li>
476 <li>Mem leak fix from Nathan Myers</li>
477 <li>Makefile: DESTDIR fix from Christophe Merlet, AMD x86_64 (Mandrake),
478 Windows (Igor), Python detection</li>
479 <li>Documentation improvements: John Fleck</li>
482 <h3>1.0.20: Aug 23 2002</h3>
484 <li>Windows makefile updates (Igor) and x86-64 (Frederic Crozat)</li>
485 <li>fixed HTML meta tag saving for Mac/IE users</li>
486 <li>possible leak patches from Nathan Myers</li>
487 <li>try to handle document('') as best as possible depending in the
489 <li>Fixed the DocBook stylesheets handling problem</li>
490 <li>Fixed a few XSLT reported errors</li>
493 <h3>1.0.19: July 6 2002</h3>
495 <li>EXSLT: dynamic functions and date support bug fixes (Mark Vakoc)</li>
496 <li>xsl:number fix: Richard Jinks</li>
497 <li>xsl:format-numbers fix: Ken Neighbors</li>
498 <li>document('') fix: bug pointed by Eric van der Vlist</li>
499 <li>xsl:message with terminate="yes" fixes: William Brack</li>
500 <li>xsl:sort order support added: Ken Neighbors</li>
501 <li>a few other bug fixes, some of them requiring the latest version of
505 <h3>1.0.18: May 27 2002</h3>
507 <li>a number of bug fixes: attributes, extra namespace declarations
508 (DocBook), xsl:include crash (Igor), documentation (Christian Cornelssen,
509 Charles Bozeman and Geert Kloosterman), element-available (Richard
511 <li>xsltproc can now list teh registered extensions thanks to Mark
513 <li>there is a new API to save directly to a string
514 xsltSaveResultToString() by Morus Walter</li>
515 <li>specific error registration function for the python API</li>
518 <h3>1.0.17: April 29 2002</h3>
520 <li>cleanup in code, XSLT debugger support and Makefiles for Windows by
522 <li>a C++ portability fix by Mark Vakoc</li>
523 <li>EXSLT date improvement and regression tests by Charles Bozeman</li>
524 <li>attempt to fix a bug in xsltProcessUserParamInternal</li>
527 <h3>1.0.16: April 15 2002</h3>
529 <li>Bug fixes: strip-space, URL in HTML output, error when xsltproc can't
531 <li>portability fixes: OSF/1, IEEE on alphas, Windows, Python bindings</li>
534 <h3>1.0.15: Mar 25 2002</h3>
536 <li>Bugfixes: XPath, python Makefile, recursive attribute sets, @foo[..]
538 <li>Debug of memory alocation with valgind</li>
539 <li>serious profiling leading to significant improvement for DocBook
541 <li>revamp of the Windows build</li>
544 <h3>1.0.14: Mar 18 2002</h3>
546 <li>Improvement in the XPath engine (libxml2-2.4.18)</li>
547 <li>Nasty bug fix related to exslt:node-set</li>
548 <li>Fixed the python Makefiles, cleanup of doc comments, Windows
549 portability fixes</li>
552 <h3>1.0.13: Mar 8 2002</h3>
554 <li>a number of bug fixes including "namespace node have no parents"</li>
555 <li>Improvement of the Python bindings</li>
556 <li>Charles Bozeman provided fixes and regression tests for exslt date
560 <h3>1.0.12: Feb 11 2002</h3>
562 <li>Fixed the makefiles especially the python module ones</li>
563 <li>half a dozen bugs fixes including 2 old ones</li>
566 <h3>1.0.11: Feb 8 2002</h3>
568 <li>Change of Licence to the <a
569 href="http://www.opensource.org/licenses/mit-license.html">MIT
571 <li>Added a beta version of the Python bindings, including support to
572 extend the engine with functions written in Python</li>
573 <li>A number of bug fixes</li>
574 <li>Charlie Bozeman provided more EXSLT functions</li>
575 <li>Portability fixes</li>
578 <h3>1.0.10: Jan 14 2002</h3>
580 <li>Windows fixes for Win32 from Igor</li>
581 <li>Fixed the Solaris compilation trouble (Albert)</li>
582 <li>Documentation changes and updates: John Fleck</li>
583 <li>Added a stringparam option to avoid escaping hell at the shell
585 <li>A few bug fixes</li>
588 <h3>1.0.9: Dec 7 2001</h3>
590 <li>Makefile patches from Peter Williams</li>
591 <li>attempt to fix the compilation problem associated to prelinking</li>
592 <li>obsoleted libxsltbreakpoint now deprecated and frozen to 1.0.8 API</li>
593 <li>xsltproc return codes are now significant, John Fleck updated the
595 <li>patch to allow as much as 40 steps in patterns (Marc Tardif), should be
596 made dynamic really</li>
597 <li>fixed a bug raised by Nik Clayton when using doctypes with HTML
599 <li>patches from Keith Isdale to interface with xsltdebugger</li>
602 <h3>1.0.8: Nov 26 2001</h3>
604 <li>fixed an annoying header problem, removed a few bugs and some code
606 <li>patches for Windows and update of Windows Makefiles by Igor</li>
607 <li>OpenVMS port instructions from John A Fotheringham</li>
608 <li>fixed some Makefiles annoyance and libraries prelinking
612 <h3>1.0.7: Nov 10 2001</h3>
614 <li>remove a compilation problem with LIBXSLT_PUBLIC</li>
615 <li>Finishing the integration steps for Keith Isdale debugger</li>
616 <li>fixes the handling of indent="no" on HTML output</li>
617 <li>fixes on the configure script and RPM spec file</li>
620 <h3>1.0.6: Oct 30 2001</h3>
622 <li>bug fixes on number formatting (Thomas), date/time functions (Bruce
624 <li>update of the Windows Makefiles (Igor)</li>
625 <li>fixed DOCTYPE generation rules for HTML output (me)</li>
628 <h3>1.0.5: Oct 10 2001</h3>
630 <li>some portability fixes, including Windows makefile updates from
632 <li>fixed a dozen bugs on XSLT and EXSLT (me and Thomas Broyer)</li>
633 <li>support for Saxon's evaluate and expressions extensions added (initial
634 contribution from Darren Graves)</li>
635 <li>better handling of XPath evaluation errors</li>
638 <h3>1.0.4: Sep 12 2001</h3>
640 <li>Documentation updates from John fleck</li>
641 <li>bug fixes (DocBook FO generation should be fixed) and portability
643 <li>Thomas Broyer improved the existing EXSLT support and added String,
644 Time and Date core functions support</li>
647 <h3>1.0.3: Aug 23 2001</h3>
649 <li>XML Catalog support see the doc</li>
650 <li>New NaN/Infinity floating point code</li>
651 <li>A few bug fixes</li>
654 <h3>1.0.2: Aug 15 2001</h3>
656 <li>lot of bug fixes, increased the testsuite</li>
657 <li>a large chunk of EXSLT is implemented</li>
658 <li>improvements on the extension framework</li>
659 <li>documentation improvements</li>
660 <li>Windows MSC projects files should be up-to-date</li>
661 <li>handle attributes inherited from the DTD by default</li>
664 <h3>1.0.1: July 24 2001</h3>
666 <li>initial EXSLT framework</li>
667 <li>better error reporting</li>
668 <li>fixed the profiler on Windows</li>
672 <h3>1.0.0: July 10 2001</h3>
674 <li>a lot of cleanup, a lot of regression tests added or fixed</li>
675 <li>added a documentation for <a href="extensions.html">writing
677 <li>fixed some variable evaluation problems (with William)</li>
678 <li>added profiling of stylesheet execution accessible as the xsltproc
679 --profile option</li>
680 <li>fixed element-available() and the implementation of the various
681 chunking methods present, Norm Walsh provided a lot of feedback</li>
682 <li>exclude-result-prefixes and namespaces output should now work as
684 <li>added support of embedded stylesheet as described in section 2.7 of the
688 <h3>0.14.0: July 5 2001</h3>
690 <li>lot of bug fixes, and code cleanup</li>
691 <li>completion of the little XSLT-1.0 features left unimplemented</li>
692 <li>Added and implemented the extension API suggested by Thomas Broyer</li>
693 <li>the Windows MSC environment should be complete</li>
694 <li>tested and optimized with a really large document (DocBook Definitive
695 Guide) libxml/libxslt should really be faster on serious workloads</li>
698 <h3>0.13.0: June 26 2001</h3>
700 <li>lots of cleanups</li>
701 <li>fixed a C++ compilation problem</li>
702 <li>couple of fixes to xsltSaveTo()</li>
703 <li>try to fix Docbook-xslt-1.4 and chunking, updated the regression test
705 <li>fixed pattern compilation and priorities problems</li>
706 <li>Patches for Windows and MSC project mostly contributed by Yon Derek</li>
707 <li>update to the Tutorial by John Fleck</li>
708 <li>William fixed bugs in templates and for-each functions</li>
709 <li>added a new interface xsltRunStylesheet() for a more flexible output
710 (incomplete), added -o option to xsltproc</li>
713 <h3>0.12.0: June 18 2001</h3>
715 <li>fixed a dozen of bugs reported</li>
716 <li>HTML generation should be quite better (requires libxml-2.3.11 upgrade
718 <li>William fixed some problems with document()</li>
719 <li>Fix namespace nodes selection and copy (requires libxml-2.3.11 upgrade
721 <li>John Fleck added a<a href="tutorial/libxslttutorial.html">
723 <li>Fixes for namespace handling when evaluating variables</li>
724 <li>XInclude global flag added to process XInclude on document() if
726 <li>made xsltproc --version more detailed</li>
729 <h3>0.11.0: June 1 2001</h3>
731 <p>Mostly a bug fix release.</p>
733 <li>integration of catalogs from xsltproc</li>
734 <li>added --version to xsltproc for bug reporting</li>
735 <li>fixed errors when handling ID in external parsed entities</li>
736 <li>document() should hopefully work correctly but ...</li>
737 <li>fixed bug with PI and comments processing</li>
738 <li>William fixed the XPath string functions when using unicode</li>
741 <h3>0.10.0: May 19 2001</h3>
743 <li>cleanups to make stylesheet read-only (not 100% complete)</li>
744 <li>fixed URI resolution in document()</li>
745 <li>force all XPath expression to be compiled at stylesheet parsing time,
746 even if unused ...</li>
747 <li>Fixed HTML default output detection</li>
748 <li>Fixed double attribute generation #54446</li>
749 <li>Fixed {{ handling in attributes #54451</li>
750 <li>More tests and speedups for DocBook document transformations</li>
751 <li>Fixed a really bad race like bug in xsltCopyTreeList()</li>
752 <li>added a documentation on the libxslt internals</li>
753 <li>William Brack and Bjorn Reese improved format-number()</li>
754 <li>Fixed multiple sort, it should really work now</li>
755 <li>added a --docbook option for SGML DocBook input (hackish)</li>
756 <li>a number of other bug fixes and regression test added as people were
760 <h3>0.9.0: May 3 2001</h3>
762 <li>lot of various bugfixes, extended the regression suite</li>
763 <li>xsltproc should work with multiple params</li>
764 <li>added an option to use xsltproc with HTML input</li>
765 <li>improved the stylesheet compilation, processing of complex stylesheets
766 should be faster</li>
767 <li>using the same stylesheet for concurrent processing on multithreaded
768 programs should work now</li>
769 <li>fixed another batch of namespace handling problems</li>
770 <li>Implemented multiple level of sorting</li>
773 <h3>0.8.0: Apr 22 2001</h3>
775 <li>fixed ansidecl.h problem</li>
776 <li>fixed unparsed-entity-uri() and generate-id()</li>
777 <li>sort semantic fixes and priority prob from William M. Brack</li>
778 <li>fixed namespace handling problems in XPath expression computations
779 (requires libxml-2.3.7)</li>
780 <li>fixes to current() and key()</li>
781 <li>other, smaller fixes, lots of testing with N Walsh DocBook HTML
785 <h3>0.7.0: Apr 10 2001</h3>
787 <li>cleanup using stricter compiler flags</li>
788 <li>command line parameter passing</li>
789 <li>fix to xsltApplyTemplates from William M. Brack</li>
790 <li>added the XSLTMark in the regression tests as well as document()</li>
793 <h3>0.6.0: Mar 22 2001</h3>
795 <li>another beta</li>
796 <li>requires 2.3.5, which provide XPath expression compilation support</li>
797 <li>document() extension should function properly</li>
798 <li>fixed a number or reported bugs</li>
801 <h3>0.5.0: Mar 10 2001</h3>
804 <li>some optimization work, for the moment 2 XSLT transform cannot use the
805 same stylesheet at the same time (to be fixed)</li>
806 <li>fixed problems with handling of tree results</li>
807 <li>fixed a reported strip-spaces problem</li>
808 <li>added more reported/fixed bugs to the test suite</li>
809 <li>incorporated William M. Brack fix for imports and global variables as
810 well as patch for with-param support in apply-templates</li>
811 <li>a bug fix on for-each</li>
814 <h3>0.4.0: Mar 1 2001</h3>
816 <li>fourth beta test, released at the same time of libxml2-2.3.3</li>
818 <li>some optimization</li>
819 <li>started implement extension support, not finished</li>
820 <li>implemented but not tested multiple file output</li>
823 <h3>0.3.0: Feb 24 2001</h3>
825 <li>third beta test, released at the same time of libxml2-2.3.2</li>
826 <li>lot of bug fixes</li>
827 <li>some optimization</li>
828 <li>added DocBook XSL based testsuite</li>
831 <h3>0.2.0: Feb 15 2001</h3>
833 <li>second beta version, released at the same time as libxml2-2.3.1</li>
834 <li>getting close to feature completion, lot of bug fixes, some in the HTML
835 and XPath support of libxml</li>
836 <li>start becoming usable for real work. This version can now regenerate
837 the XML 2e HTML from the original XML sources and the associated
839 href="http://www.w3.org/TR/REC-xml#b4d250b6c21">section I of the XML
841 <li>Still misses extension element/function/prefixes support. Support of
842 key() and document() is not complete</li>
845 <h3>0.1.0: Feb 8 2001</h3>
847 <li>first beta version, released at the same time as libxml2-2.3.0</li>
848 <li>lots of bug fixes, first "testing" version, but incomplete</li>
851 <h3>0.0.1: Jan 25 2001</h3>
853 <li>first alpha version released at the same time as libxml2-2.2.12</li>
854 <li>Framework in place, should work on simple examples, but far from being
855 feature complete</li>
858 <h2><a name="xsltproc">The xsltproc tool</a></h2>
860 <p>This program is the simplest way to use libxslt: from the command line. It
861 is also used for doing the regression tests of the library.</p>
863 <p>It takes as first argument the path or URL to an XSLT stylesheet, the next
864 arguments are filenames or URIs of the inputs to be processed. The output of
865 the processing is redirected on the standard output. There is actually a few
866 more options available:</p>
867 <pre>orchis:~ -> xsltproc
868 Usage: xsltproc [options] stylesheet file [file ...]
870 --version or -V: show the version of libxml and libxslt used
871 --verbose or -v: show logs of what's happening
872 --output file or -o file: save to a given file
873 --timing: display the time used
874 --repeat: run the transformation 20 times
875 --debug: dump the tree of the result instead
876 --novalid: skip the Dtd loading phase
877 --noout: do not dump the result
878 --maxdepth val : increase the maximum depth
879 --html: the input document is(are) an HTML file(s)
880 --docbook: the input document is SGML docbook
881 --param name value : pass a (parameter,value) pair
882 --nonet refuse to fetch DTDs or entities over network
883 --warnnet warn against fetching over the network
884 --catalogs : use the catalogs from $SGML_CATALOG_FILES
885 --xinclude : do XInclude processing on document intput
886 --profile or --norman : dump profiling informations
889 <h2><a name="DocBook">DocBook</a></h2>
891 <p><img src="duck.png" align="right" alt="The duck picture"></p>
893 <p><a href="http://www.oasis-open.org/committees/docbook/">DocBook</a> is an
894 XML/SGML vocabulary particularly well suited to books and papers about
895 computer hardware and software.</p>
897 <p>xsltproc and libxslt are not specifically dependant on DocBook, but since
898 a lot of people use xsltproc and libxml2 for DocBook formatting, here are a
899 few pointers and informations which may be helpful:</p>
901 <li>The <a href="http://www.oasis-open.org/committees/docbook/">DocBook
902 homepage at Oasis</a> you should find pointers there on all the lastest
903 versions of the DTDs and XSLT stylesheets</li>
904 <li><a href="http://www.docbook.org/">DocBook: The Definitive Guide</a> is
905 the official reference documentation for DocBook.</li>
907 href="https://sourceforge.net/docman/index.php?group_id=21935">DocBook
908 Open Repository</a> contains a lot of informations about DocBook</li>
909 <li>Bob Stayton provides a <a href="http://www.sagehill.net/">lot of
910 resources</a> and consulting services around DocBook.</li>
911 <li>Here is a <a href="/buildDocBookCatalog">shell script</a> to generate
912 XML Catalogs for DocBook 4.1.2 . If it can write to the /etc/xml/
913 directory, it will set-up /etc/xml/catalog and /etc/xml/docbook based on
914 the resources found on the system. Otherwise it will just create
915 ~/xmlcatalog and ~/dbkxmlcatalog and doing:
916 <p><code>export XMLCATALOG=$HOME/xmlcatalog</code></p>
917 <p>should allow to process DocBook documentations without requiring
918 network accesses for the DTd or stylesheets</p>
920 <li>I have uploaded <a href="ftp://xmlsoft.org/test/dbk412catalog.tar.gz">a
921 small tarball</a> containing XML Catalogs for DocBook 4.1.2 which seems
922 to work fine for me too</li>
923 <li>Informations on installing a <a
924 href="http://ourworld.compuserve.com/homepages/hoenicka_markus/ntsgml.html">Windows
925 DocBook processing setup</a> based on Cygwin (using the binaries from the
926 official Windows port should be possible too)</li>
927 <li>Alexander Kirillov's page on <a
928 href="http://www.math.sunysb.edu/~kirillov/dbxml/">Using DocBook XML
929 4.1.2</a> (RPM packages)</li>
930 <li>Tim Waugh's <a href="http://cyberelk.net/tim/xmlto/">xmlto front-end
931 conversion script</a></li>
932 <li>Linux Documentation Project <a
933 href="http://www.linuxdoc.org/HOWTO/mini/DocBook-Install/">
934 DocBook-Install-mini-HOWTO</a></li>
935 <li>ScrollKeeper the open documentation cataloging project has a <a
936 href="http://scrollkeeper.sourceforge.net/docbook.shtml">DocBook
938 <li>Dan York presentation on <a
939 href="http://www.lodestar2.com/people/dyork/talks/2001/xugo/docbook/index.html">Publishing
940 using DocBook XML</a></li>
943 <p>Do not use the --docbook option of xsltproc to process XML DocBook
944 documents, this option is only intended to provide some (limited) support of
945 the SGML version of DocBook.</p>
947 <p>Points which are not DocBook specific but still worth mentionning
950 <li>if you think DocBook processing time is too slow, make sure you have
951 XML Catalogs pointing to a local installation of the DTD of DocBook.
952 Check the <a href="http://xmlsoft.org/catalog.html">XML Catalog page</a>
953 to understand more on this subject.</li>
954 <li>before processing a new document, use the command
955 <p><code>xmllint --valid --noout path_to_document</code></p>
956 <p>to make sure that your input is valid DocBook. And fixes the errors
957 before processing further. Note that XSLT processing may work correctly
958 with some forms of validity errors left, but in general it can give
959 troubles on output.</p>
963 <h2><a name="API">The programming API</a></h2>
965 <p>Okay this section is clearly incomplete. But integrating libxslt into your
966 application should be relatively easy. First check the few steps described
967 below, then for more detailed informations, look at the<a
968 href="html/libxslt-lib.html"> generated pages</a> for the API and the source
969 of libxslt/xsltproc.c and the <a
970 href="tutorial/libxslttutorial.html">tutorial</a>.</p>
972 <p>Basically doing an XSLT transformation can be done in a few steps:</p>
974 <li>configure the parser for XSLT:
975 <p>xmlSubstituteEntitiesDefault(1);</p>
976 <p>xmlLoadExtDtdDefaultValue = 1;</p>
978 <li>parse the stylesheet with xsltParseStylesheetFile()</li>
979 <li>parse the document with xmlParseFile()</li>
980 <li>apply the stylesheet using xsltApplyStylesheet()</li>
981 <li>save the result using xsltSaveResultToFile() if needed set
982 xmlIndentTreeOutput to 1</li>
985 <p>Steps 2,3, and 5 will probably need to be changed depending on you
986 processing needs and environment for example if reading/saving from/to
987 memory, or if you want to apply XInclude processing to the stylesheet or
990 <h2><a name="Python">Python and bindings</a></h2>
992 <p>There is a number of language bindings and wrappers available for libxml2,
993 the list below is not exhaustive. Please contact the <a
994 href="http://mail.gnome.org/mailman/listinfo/xml-bindings">xml-bindings@gnome.org</a>
995 (<a href="http://mail.gnome.org/archives/xml-bindings/">archives</a>) in
996 order to get updates to this list or to discuss the specific topic of libxml2
997 or libxslt wrappers or bindings:</p>
1000 href="http://mail.gnome.org/archives/xml/2001-March/msg00014.html">Matt
1001 Sergeant</a> developped <a href="http://axkit.org/download/">XML::LibXML
1002 and XML::LibXSLT</a>, Perl wrappers for libxml2/libxslt as part of the <a
1003 href="http://axkit.com/">AxKit XML application server</a></li>
1004 <li><a href="mailto:dkuhlman@cutter.rexx.com">Dave Kuhlman</a> provides and
1005 earlier version of the libxml/libxslt <a
1006 href="http://www.rexx.com/~dkuhlman">wrappers for Python</a></li>
1007 <li>Petr Kozelka provides <a
1008 href="http://sourceforge.net/projects/libxml2-pas">Pascal units to glue
1009 libxml2</a> with Kylix, Delphi and other Pascal compilers</li>
1010 <li>Wai-Sun "Squidster" Chia provides <a
1011 href="http://www.rubycolor.org/arc/redist/">bindings for Ruby</a> and
1012 libxml2 bindings are also available in Ruby through the <a
1013 href="http://libgdome-ruby.berlios.de/">libgdome-ruby</a> module
1014 maintained by Tobias Peters.</li>
1015 <li>Steve Ball and contributors maintains <a
1016 href="http://tclxml.sourceforge.net/">libxml2 and libxslt bindings for
1018 <li><a href="mailto:xmlwrapp@pmade.org">Peter Jones</a> maintains C++
1019 bindings for libxslt within <a
1020 href="http://pmade.org/pjones/software/xmlwrapp/">xmlwrapp</a></li>
1021 <li><a href="phillim2@comcast.net">Mike Phillips</a> provides a module
1022 using <a href="http://siasl.dyndns.org/projects/projects.html">libxslt
1024 <li><a href="http://savannah.gnu.org/projects/classpathx/">LibxmlJ</a> is
1025 an effort to create a 100% JAXP-compatible Java wrapper for libxml2 and
1026 libxslt as part of GNU ClasspathX project.</li>
1027 <li>Patrick McPhee provides Rexx bindings fof libxml2 and libxslt, look for
1028 <a href="http://www.interlog.com/~ptjm/software.html">RexxXML</a>.</li>
1031 <p>The libxslt Python module depends on the <a
1032 href="http://xmlsoft.org/python.html">libxml2 Python</a> module.</p>
1034 <p>The distribution includes a set of Python bindings, which are garanteed to
1035 be maintained as part of the library in the future, though the Python
1036 interface have not yet reached the completeness of the C API.</p>
1038 <p><a href="mailto:stephane.bidoul@softwareag.com">Stéphane Bidoul</a>
1039 maintains <a href="http://users.skynet.be/sbi/libxml-python/">a Windows port
1040 of the Python bindings</a>.</p>
1042 <p>Note to people interested in building bindings, the API is formalized as
1043 <a href="libxslt-api.xml">an XML API description file</a> which allows to
1044 automate a large part of the Python bindings, this includes function
1045 descriptions, enums, structures, typedefs, etc... The Python script used to
1046 build the bindings is python/generator.py in the source distribution.</p>
1048 <p>To install the Python bindings there are 2 options:</p>
1050 <li>If you use an RPM based distribution, simply install the <a
1051 href="http://rpmfind.net/linux/rpm2html/search.php?query=libxml2-python">libxml2-python
1053 href="http://rpmfind.net/linux/rpm2html/search.php?query=libxslt-python">libxslt-python
1055 <li>Otherwise use the <a href="ftp://xmlsoft.org/python/">libxml2-python
1056 module distribution</a> corresponding to your installed version of
1057 libxml2 and libxslt. Note that to install it you will need both libxml2
1058 and libxslt installed and run "python setup.py build install" in the
1062 <p>The distribution includes a set of examples and regression tests for the
1063 python bindings in the <code>python/tests</code> directory. Here are some
1064 excepts from those tests:</p>
1068 <p>This is a basic test of XSLT interfaces: loading a stylesheet and a
1069 document, transforming the document and saving the result.</p>
1073 styledoc = libxml2.parseFile("test.xsl")
1074 style = libxslt.parseStylesheetDoc(styledoc)
1075 doc = libxml2.parseFile("test.xml")
1076 result = style.applyStylesheet(doc, None)
1077 style.saveResultToFilename("foo", result, 0)
1078 style.freeStylesheet()
1080 result.freeDoc()</pre>
1082 <p>The Python module is called libxslt, you will also need the libxml2 module
1083 for the operations on XML trees. Let's have a look at the objects manipulated
1084 in that example and how is the processing done:</p>
1086 <li><code>styledoc</code> : is a libxml2 document tree. It is obtained by
1087 parsing the XML file "test.xsl" containing the stylesheet.</li>
1088 <li><code>style</code> : this is a precompiled stylesheet ready to be used
1089 by the following transformations (note the plural form, multiple
1090 transformations can resuse the same stylesheet).</li>
1091 <li><code>doc</code> : this is the document to apply the transformation to.
1092 In this case it is simply generated by parsing it from a file but any
1093 other processing is possible as long as one get a libxml2 Doc. Note that
1094 HTML tree are suitable for XSLT processing in libxslt. This is actually
1095 how this page is generated !</li>
1096 <li><code>result</code> : this is a document generated by applying the
1097 stylesheet to the document. Note that some of the stylesheet informations
1098 may be related to the serialization of that document and as in this
1099 example a specific saveResultToFilename() method of the stylesheet should
1100 be used to save it to a file (in that case to "foo").</li>
1103 <p>Also note the need to explicitely deallocate documents with freeDoc()
1104 except for the stylesheet document which is freed when its compiled form is
1105 garbage collected.</p>
1107 <h3>extfunc.py:</h3>
1109 <p>This one is a far more complex test. It shows how to modify the behaviour
1110 of an XSLT transformation by passing parameters and how to extend the XSLT
1111 engine with functions defined in python:</p>
1121 # Small check to verify the context is correcly accessed
1124 pctxt = libxslt.xpathParserContext(_obj=ctx)
1125 ctxt = pctxt.context()
1126 tctxt = ctxt.transformContext()
1127 nodeName = tctxt.insertNode().name
1131 return string.upper(str)
1133 libxslt.registerExtModuleFunction("foo", "http://example.com/foo", f)</pre>
1135 <p>This code defines and register an extension function. Note that the
1136 function can be bound to any name (foo) and how the binding is also
1137 associated to a namespace name "http://example.com/foo". From an XSLT point
1138 of view the function just returns an upper case version of the string passed
1139 as a parameter. But the first part of the function also read some contextual
1140 information from the current XSLT processing environement, in that case it
1141 looks for the current insertion node in the resulting output (either the
1142 resulting document or the Result Value Tree being generated), and saves it to
1143 a global variable for checking that the access actually worked.</p>
1145 <p>For more informations on the xpathParserContext and transformContext
1146 objects check the <a href="internals.html">libray internals description</a>.
1147 The pctxt is actually an object from a class derived from the
1148 libxml2.xpathParserContext() with just a couple more properties including the
1149 possibility to look up the XSLT transformation context from the XPath
1151 <pre>styledoc = libxml2.parseDoc("""
1152 <xsl:stylesheet version='1.0'
1153 xmlns:xsl='http://www.w3.org/1999/XSL/Transform'
1154 xmlns:foo='http://example.com/foo'
1155 xsl:exclude-result-prefixes='foo'>
1157 <xsl:param name='bar'>failure</xsl:param>
1158 <xsl:template match='/'>
1159 <article><xsl:value-of select='foo:foo($bar)'/></article>
1160 </xsl:template>
1161 </xsl:stylesheet>
1164 <p>Here is a simple example of how to read an XML document from a python
1165 string with libxml2. Note how this stylesheet:</p>
1167 <li>Uses a global parameter <code>bar</code></li>
1168 <li>Reference the extension function f</li>
1169 <li>how the Namespace name "http://example.com/foo" has to be bound to a
1171 <li>how that prefix is excluded from the output</li>
1172 <li>how the function is called from the select</li>
1174 <pre>style = libxslt.parseStylesheetDoc(styledoc)
1175 doc = libxml2.parseDoc("<doc/>")
1176 result = style.applyStylesheet(doc, { "bar": "'success'" })
1177 style.freeStylesheet()
1180 <p>that part is identical, to the basic example except that the
1181 transformation is passed a dictionnary of parameters. Note that the string
1182 passed "success" had to be quoted, otherwise it is interpreted as an XPath
1183 query for the childs of root named "success".</p>
1184 <pre>root = result.children
1185 if root.name != "article":
1186 print "Unexpected root node name"
1188 if root.content != "SUCCESS":
1189 print "Unexpected root node content, extension function failed"
1191 if nodeName != 'article':
1192 print "The function callback failed to access its context"
1195 result.freeDoc()</pre>
1197 <p>That part just verifies that the transformation worked, that the parameter
1198 got properly passed to the engine, that the function f() got called and that
1199 it properly accessed the context to find the name of the insertion node.</p>
1201 <h3>pyxsltproc.py:</h3>
1203 <p>this module is a bit too long to be described there but it is basically a
1204 rewrite of the xsltproc command line interface of libxslt in Python. It
1205 provides nearly all the functionalities of xsltproc and can be used as a base
1206 module to write Python customized XSLT processors. One of the thing to notice
1208 <pre>libxml2.lineNumbersDefault(1)
1209 libxml2.substituteEntitiesDefault(1)</pre>
1211 <p>those two calls in the main() function are needed to force the libxml2
1212 processor to generate DOM trees compliant with the XPath data model.</p>
1214 <h2><a name="Internals">Library internals</a></h2>
1216 <h3>Table of contents</h3>
1218 <li><a href="internals.html#Introducti">Introduction</a></li>
1219 <li><a href="internals.html#Basics">Basics</a></li>
1220 <li><a href="internals.html#Keep">Keep it simple stupid</a></li>
1221 <li><a href="internals.html#libxml">The libxml nodes</a></li>
1222 <li><a href="internals.html#XSLT">The XSLT processing steps</a></li>
1223 <li><a href="internals.html#XSLT1">The XSLT stylesheet compilation</a></li>
1224 <li><a href="internals.html#XSLT2">The XSLT template compilation</a></li>
1225 <li><a href="internals.html#processing">The processing itself</a></li>
1226 <li><a href="internals.html#XPath">XPath expressions compilation</a></li>
1227 <li><a href="internals.html#XPath1">XPath interpretation</a></li>
1228 <li><a href="internals.html#Descriptio">Description of XPath
1230 <li><a href="internals.html#XPath3">XPath functions</a></li>
1231 <li><a href="internals.html#stack">The variables stack frame</a></li>
1232 <li><a href="internals.html#Extension">Extension support</a></li>
1233 <li><a href="internals.html#Futher">Further reading</a></li>
1234 <li><a href="internals.html#TODOs">TODOs</a></li>
1237 <h3><a name="Introducti2">Introduction</a></h3>
1239 <p>This document describes the processing of <a
1240 href="http://xmlsoft.org/XSLT/">libxslt</a>, the <a
1241 href="http://www.w3.org/TR/xslt">XSLT</a> C library developed for the <a
1242 href="http://www.gnome.org/">Gnome</a> project.</p>
1244 <p>Note: this documentation is by definition incomplete and I am not good at
1245 spelling, grammar, so patches and suggestions are <a
1246 href="mailto:veillard@redhat.com">really welcome</a>.</p>
1248 <h3><a name="Basics1">Basics</a></h3>
1250 <p>XSLT is a transformation language. It takes an input document and a
1251 stylesheet document and generates an output document:</p>
1253 <p align="center"><img src="processing.gif"
1254 alt="the XSLT processing model"></p>
1256 <p>Libxslt is written in C. It relies on <a
1257 href="http://www.xmlsoft.org/">libxml</a>, the XML C library for Gnome, for
1258 the following operations:</p>
1260 <li>parsing files</li>
1261 <li>building the in-memory DOM structure associated with the documents
1263 <li>the XPath implementation</li>
1264 <li>serializing back the result document to XML and HTML. (Text is handled
1268 <h3><a name="Keep1">Keep it simple stupid</a></h3>
1270 <p>Libxslt is not very specialized. It is built under the assumption that all
1271 nodes from the source and output document can fit in the virtual memory of
1272 the system. There is a big trade-off there. It is fine for reasonably sized
1273 documents but may not be suitable for large sets of data. The gain is that it
1274 can be used in a relatively versatile way. The input or output may never be
1275 serialized, but the size of documents it can handle are limited by the size
1276 of the memory available.</p>
1278 <p>More specialized memory handling approaches are possible, like building
1279 the input tree from a serialization progressively as it is consumed,
1280 factoring repetitive patterns, or even on-the-fly generation of the output as
1281 the input is parsed but it is possible only for a limited subset of the
1282 stylesheets. In general the implementation of libxslt follows the following
1285 <li>KISS (keep it simple stupid)</li>
1286 <li>when there is a clear bottleneck optimize on top of this simple
1287 framework and refine only as much as is needed to reach the expected
1291 <p>The result is not that bad, clearly one can do a better job but more
1292 specialized too. Most optimization like building the tree on-demand would
1293 need serious changes to the libxml XPath framework. An easy step would be to
1294 serialize the output directly (or call a set of SAX-like output handler to
1295 keep this a flexible interface) and hence avoid the memory consumption of the
1298 <h3><a name="libxml">The libxml nodes</a></h3>
1300 <p>DOM-like trees, as used and generated by libxml and libxslt, are
1301 relatively complex. Most node types follow the given structure except a few
1302 variations depending on the node type:</p>
1304 <p align="center"><img src="node.gif" alt="description of a libxml node"></p>
1306 <p>Nodes carry a <strong>name</strong> and the node <strong>type</strong>
1307 indicates the kind of node it represents, the most common ones are:</p>
1309 <li>document nodes</li>
1310 <li>element nodes</li>
1314 <p>For the XSLT processing, entity nodes should not be generated (i.e. they
1315 should be replaced by their content). Most nodes also contains the following
1316 "navigation" informations:</p>
1318 <li>the containing <strong>doc</strong>ument</li>
1319 <li>the <strong>parent</strong> node</li>
1320 <li>the first <strong>children</strong> node</li>
1321 <li>the <strong>last</strong> children node</li>
1322 <li>the <strong>prev</strong>ious sibling</li>
1323 <li>the following sibling (<strong>next</strong>)</li>
1326 <p>Elements nodes carries the list of attributes in the properties, an
1327 attribute itself holds the navigation pointers and the children list (the
1328 attribute value is not represented as a simple string to allow usage of
1329 entities references).</p>
1331 <p>The <strong>ns</strong> points to the namespace declaration for the
1332 namespace associated to the node, <strong>nsDef</strong> is the linked list
1333 of namespace declaration present on element nodes.</p>
1335 <p>Most nodes also carry an <strong>_private</strong> pointer which can be
1336 used by the application to hold specific data on this node.</p>
1338 <h3><a name="XSLT">The XSLT processing steps</a></h3>
1340 <p>There are a few steps which are clearly decoupled at the interface
1343 <li>parse the stylesheet and generate a DOM tree</li>
1344 <li>take the stylesheet tree and build a compiled version of it (the
1345 compilation phase)</li>
1346 <li>take the input and generate a DOM tree</li>
1347 <li>process the stylesheet against the input tree and generate an output
1349 <li>serialize the output tree</li>
1352 <p>A few things should be noted here:</p>
1354 <li>the steps 1/ 3/ and 5/ are optional</li>
1355 <li>the stylesheet obtained at 2/ can be reused by multiple processing 4/
1356 (and this should also work in threaded programs)</li>
1357 <li>the tree provided in 2/ should never be freed using xmlFreeDoc, but by
1358 freeing the stylesheet.</li>
1359 <li>the input tree 4/ is not modified except the _private field which may
1360 be used for labelling keys if used by the stylesheet</li>
1363 <h3><a name="XSLT1">The XSLT stylesheet compilation</a></h3>
1365 <p>This is the second step described. It takes a stylesheet tree, and
1366 "compiles" it. This associates to each node a structure stored in the
1367 _private field and containing information computed in the stylesheet:</p>
1369 <p align="center"><img src="stylesheet.gif"
1370 alt="a compiled XSLT stylesheet"></p>
1372 <p>One xsltStylesheet structure is generated per document parsed for the
1373 stylesheet. XSLT documents allow includes and imports of other documents,
1374 imports are stored in the <strong>imports</strong> list (hence keeping the
1375 tree hierarchy of includes which is very important for a proper XSLT
1376 processing model) and includes are stored in the <strong>doclist</strong>
1377 list. An imported stylesheet has a parent link to allow browsing of the
1380 <p>The DOM tree associated to the document is stored in <strong>doc</strong>.
1381 It is preprocessed to remove ignorable empty nodes and all the nodes in the
1382 XSLT namespace are subject to precomputing. This usually consist of
1383 extracting all the context information from the context tree (attributes,
1384 namespaces, XPath expressions), and storing them in an xsltStylePreComp
1385 structure associated to the <strong>_private</strong> field of the node.</p>
1387 <p>A couple of notable exceptions to this are XSLT template nodes (more on
1388 this later) and attribute value templates. If they are actually templates,
1389 the value cannot be computed at compilation time. (Some preprocessing could
1390 be done like isolation and preparsing of the XPath subexpressions but it's
1393 <p>The xsltStylePreComp structure also allows storing of the precompiled form
1394 of an XPath expression that can be associated to an XSLT element (more on
1397 <h3><a name="XSLT2">The XSLT template compilation</a></h3>
1399 <p>A proper handling of templates lookup is one of the keys of fast XSLT
1400 processing. (Given a node in the source document this is the process of
1401 finding which templates should be applied to this node.) Libxslt follows the
1402 hint suggested in the <a href="http://www.w3.org/TR/xslt#patterns">5.2
1403 Patterns</a> section of the XSLT Recommendation, i.e. it doesn't evaluate it
1404 as an XPath expression but tokenizes it and compiles it as a set of rules to
1405 be evaluated on a candidate node. There usually is an indication of the node
1406 name in the last step of this evaluation and this is used as a key check for
1407 the match. As a result libxslt builds a relatively more complex set of
1408 structures for the templates:</p>
1410 <p align="center"><img src="templates.gif"
1411 alt="The templates related structure"></p>
1413 <p>Let's describe a bit more closely what is built. First the xsltStylesheet
1414 structure holds a pointer to the template hash table. All the XSLT patterns
1415 compiled in this stylesheet are indexed by the value of the the target
1416 element (or attribute, pi ...) name, so when a element or an attribute "foo"
1417 needs to be processed the lookup is done using the name as a key.</p>
1419 <p>Each of the patterns is compiled into an xsltCompMatch structure. It holds
1420 the set of rules based on the tokenization of the pattern stored in reverse
1421 order (matching is easier this way). It also holds some information about the
1422 previous matches used to speed up the process when one iterates over a set of
1423 siblings. (This optimization may be defeated by trashing when running
1424 threaded computation, it's unclear that this is a big deal in practice.)
1425 Predicate expressions are not compiled at this stage, they may be at run-time
1426 if needed, but in this case they are compiled as full XPath expressions (the
1427 use of some fixed predicate can probably be optimized, they are not yet).</p>
1429 <p>The xsltCompMatch are then stored in the hash table, the clash list is
1430 itself sorted by priority of the template to implement "naturally" the XSLT
1433 <p>Associated to the compiled pattern is the xsltTemplate itself containing
1434 the information required for the processing of the pattern including, of
1435 course, a pointer to the list of elements used for building the pattern
1438 <p>Last but not least a number of patterns do not fit in the hash table
1439 because they are not associated to a name, this is the case for patterns
1440 applying to the root, any element, any attributes, text nodes, pi nodes, keys
1441 etc. Those are stored independently in the stylesheet structure as separate
1442 linked lists of xsltCompMatch.</p>
1444 <h3><a name="processing">The processing itself</a></h3>
1446 <p>The processing is defined by the XSLT specification (the basis of the
1447 algorithm is explained in <a
1448 href="http://www.w3.org/TR/xslt#section-Introduction">the Introduction</a>
1449 section). Basically it works by taking the root of the input document and
1450 applying the following algorithm:</p>
1452 <li>Finding the template applying to it. This is a lookup in the template
1453 hash table, walking the hash list until the node satisfies all the steps
1454 of the pattern, then checking the appropriate(s) global templates to see
1455 if there isn't a higher priority rule to apply</li>
1456 <li>If there is no template, apply the default rule (recurse on the
1458 <li>else walk the content list of the selected templates, for each of them:
1460 <li>if the node is in the XSLT namespace then the node has a _private
1461 field pointing to the preprocessed values, jump to the specific
1463 <li>if the node is in an extension namespace, look up the associated
1465 <li>otherwise copy the node.</li>
1467 <p>The closure is usually done through the XSLT
1468 <strong>apply-templates</strong> construct recursing by applying the
1469 adequate template on the input node children or on the result of an
1470 associated XPath selection lookup.</p>
1474 <p>Note that large parts of the input tree may not be processed by a given
1475 stylesheet and that on the opposite some may be processed multiple times.
1476 (This often is the case when a Table of Contents is built).</p>
1478 <p>The module <code>transform.c</code> is the one implementing most of this
1479 logic. <strong>xsltApplyStylesheet()</strong> is the entry point, it
1480 allocates an xsltTransformContext containing the following:</p>
1482 <li>a pointer to the stylesheet being processed</li>
1483 <li>a stack of templates</li>
1484 <li>a stack of variables and parameters</li>
1485 <li>an XPath context</li>
1486 <li>the template mode</li>
1487 <li>current document</li>
1488 <li>current input node</li>
1489 <li>current selected node list</li>
1490 <li>the current insertion points in the output document</li>
1491 <li>a couple of hash tables for extension elements and functions</li>
1494 <p>Then a new document gets allocated (HTML or XML depending on the type of
1495 output), the user parameters and global variables and parameters are
1496 evaluated. Then <strong>xsltProcessOneNode()</strong> which implements the
1497 1-2-3 algorithm is called on the root element of the input. Step 1/ is
1498 implemented by calling <strong>xsltGetTemplate()</strong>, step 2/ is
1499 implemented by <strong>xsltDefaultProcessOneNode()</strong> and step 3/ is
1500 implemented by <strong>xsltApplyOneTemplate()</strong>.</p>
1502 <h3><a name="XPath">XPath expression compilation</a></h3>
1504 <p>The XPath support is actually implemented in the libxml module (where it
1505 is reused by the XPointer implementation). XPath is a relatively classic
1506 expression language. The only uncommon feature is that it is working on XML
1507 trees and hence has specific syntax and types to handle them.</p>
1509 <p>XPath expressions are compiled using <strong>xmlXPathCompile()</strong>.
1510 It will take an expression string in input and generate a structure
1511 containing the parsed expression tree, for example the expression:</p>
1512 <pre>/doc/chapter[title='Introduction']</pre>
1514 <p>will be compiled as</p>
1515 <pre>Compiled Expression : 10 elements
1517 COLLECT 'child' 'name' 'node' chapter
1518 COLLECT 'child' 'name' 'node' doc
1523 COLLECT 'child' 'name' 'node' title
1525 ELEM Object is a string : Introduction
1526 COLLECT 'child' 'name' 'node' title
1529 <p>This can be tested using the <code>testXPath</code> command (in the
1530 libxml codebase) using the <code>--tree</code> option.</p>
1532 <p>Again, the KISS approach is used. No optimization is done. This could be
1533 an interesting thing to add. <a
1534 href="http://www-106.ibm.com/developerworks/library/x-xslt2/?dwzone=x?open&l=132%2ct=gr%2c+p=saxon">Michael
1535 Kay describes</a> a lot of possible and interesting optimizations done in
1536 Saxon which would be possible at this level. I'm unsure they would provide
1537 much gain since the expressions tends to be relatively simple in general and
1538 stylesheets are still hand generated. Optimizations at the interpretation
1539 sounds likely to be more efficient.</p>
1541 <h3><a name="XPath1">XPath interpretation</a></h3>
1543 <p>The interpreter is implemented by <strong>xmlXPathCompiledEval()</strong>
1544 which is the front-end to <strong>xmlXPathCompOpEval()</strong> the function
1545 implementing the evaluation of the expression tree. This evaluation follows
1546 the KISS approach again. It's recursive and calls
1547 <strong>xmlXPathNodeCollectAndTest()</strong> to collect nodes set when
1548 evaluating a <code>COLLECT</code> node.</p>
1550 <p>An evaluation is done within the framework of an XPath context stored in
1551 an <strong>xmlXPathContext</strong> structure, in the framework of a
1552 transformation the context is maintained within the XSLT context. Its content
1553 follows the requirements from the XPath specification:</p>
1555 <li>the current document</li>
1556 <li>the current node</li>
1557 <li>a hash table of defined variables (but not used by XSLT)</li>
1558 <li>a hash table of defined functions</li>
1559 <li>the proximity position (the place of the node in the current node
1561 <li>the context size (the size of the current node list)</li>
1562 <li>the array of namespace declarations in scope (there also is a namespace
1563 hash table but it is not used in the XSLT transformation).</li>
1566 <p>For the purpose of XSLT an <strong>extra</strong> pointer has been added
1567 allowing to retrieve the XSLT transformation context. When an XPath
1568 evaluation is about to be performed, an XPath parser context is allocated
1569 containing and XPath object stack (this is actually an XPath evaluation
1570 context, this is a remain of the time where there was no separate parsing and
1571 evaluation phase in the XPath implementation). Here is an overview of the set
1572 of contexts associated to an XPath evaluation within an XSLT
1575 <p align="center"><img src="contexts.gif"
1576 alt="The set of contexts associated "></p>
1578 <p>Clearly this is a bit too complex and confusing and should be refactored
1579 at the next set of binary incompatible releases of libxml. For example the
1580 xmlXPathCtxt has a lot of unused parts and should probably be merged with
1581 xmlXPathParserCtxt.</p>
1583 <h3><a name="Descriptio">Description of XPath Objects</a></h3>
1585 <p>An XPath expression manipulates XPath objects. XPath defines the default
1586 types boolean, numbers, strings and node sets. XSLT adds the result tree
1587 fragment type which is basically an unmodifiable node set.</p>
1589 <p>Implementation-wise, libxml follows again a KISS approach, the
1590 xmlXPathObject is a structure containing a type description and the various
1591 possibilities. (Using an enum could have gained some bytes.) In the case of
1592 node sets (or result tree fragments), it points to a separate xmlNodeSet
1593 object which contains the list of pointers to the document nodes:</p>
1595 <p align="center"><img src="object.gif"
1596 alt="An Node set object pointing to "></p>
1598 <p>The <a href="http://xmlsoft.org/html/libxml-xpath.html">XPath API</a> (and
1599 its <a href="http://xmlsoft.org/html/libxml-xpathinternals.html">'internal'
1600 part</a>) includes a number of functions to create, copy, compare, convert or
1601 free XPath objects.</p>
1603 <h3><a name="XPath3">XPath functions</a></h3>
1605 <p>All the XPath functions available to the interpreter are registered in the
1606 function hash table linked from the XPath context. They all share the same
1608 <pre>void xmlXPathFunc (xmlXPathParserContextPtr ctxt, int nargs);</pre>
1610 <p>The first argument is the XPath interpretation context, holding the
1611 interpretation stack. The second argument defines the number of objects
1612 passed on the stack for the function to consume (last argument is on top of
1615 <p>Basically an XPath function does the following:</p>
1617 <li>check <code>nargs</code> for proper handling of errors or functions
1618 with variable numbers of parameters</li>
1619 <li>pop the parameters from the stack using <code>obj =
1620 valuePop(ctxt);</code></li>
1621 <li>do the function specific computation</li>
1622 <li>push the result parameter on the stack using <code>valuePush(ctxt,
1624 <li>free up the input parameters with
1625 <code>xmlXPathFreeObject(obj);</code></li>
1629 <p>Sometime the work can be done directly by modifying in-situ the top object
1630 on the stack <code>ctxt->value</code>.</p>
1632 <h3><a name="stack">The XSLT variables stack frame</a></h3>
1634 <p>Not to be confused with XPath object stack, this stack holds the XSLT
1635 variables and parameters as they are defined through the recursive calls of
1636 call-template, apply-templates and default templates. This is used to define
1637 the scope of variables being called.</p>
1639 <p>This part seems to be the most urgent attention right now, first it is
1640 done in a very inefficient way since the location of the variables and
1641 parameters within the stylesheet tree is still done at run time (it really
1642 should be done statically at compile time), and I am still unsure that my
1643 understanding of the template variables and parameter scope is actually
1646 <p>This part of the documentation is still to be written once this part of
1647 the code will be stable. <span
1648 style="background-color: #FF0000">TODO</span></p>
1650 <h3><a name="Extension">Extension support</a></h3>
1652 <p>There is a separate document explaining <a href="extensions.html">how the
1653 extension support works</a>.</p>
1655 <h3><a name="Futher">Further reading</a></h3>
1657 <p>Michael Kay wrote <a
1658 href="http://www-106.ibm.com/developerworks/library/x-xslt2/?dwzone=x?open&l=132%2ct=gr%2c+p=saxon">a
1659 really interesting article on Saxon internals</a> and the work he did on
1660 performance issues. I wishes I had read it before starting libxslt design (I
1661 would probably have avoided a few mistakes and progressed faster). A lot of
1662 the ideas in his papers should be implemented or at least tried in
1665 <p>The <a href="http://xmlsoft.org/">libxml documentation</a>, especially <a
1666 href="http://xmlsoft.org/xmlio.html">the I/O interfaces</a> and the <a
1667 href="http://xmlsoft.org/xmlmem.html">memory management</a>.</p>
1669 <h3><a name="TODOs">TODOs</a></h3>
1671 <p>redesign the XSLT stack frame handling. Far too much work is done at
1672 execution time. Similarly for the attribute value templates handling, at
1673 least the embedded subexpressions ought to be precompiled.</p>
1675 <p>Allow output to be saved to a SAX like output (this notion of SAX like API
1676 for output should be added directly to libxml).</p>
1678 <p>Implement and test some of the optimization explained by Michael Kay
1681 <li>static slot allocation on the stack frame</li>
1682 <li>specific boolean interpretation of an XPath expression</li>
1683 <li>some of the sorting optimization</li>
1684 <li>Lazy evaluation of location path. (this may require more changes but
1685 sounds really interesting. XT does this too.)</li>
1686 <li>Optimization of an expression tree (This could be done as a completely
1687 independent module.)</li>
1692 <p>Error reporting, there is a lot of case where the XSLT specification
1693 specify that a given construct is an error are not checked adequately by
1694 libxslt. Basically one should do a complete pass on the XSLT spec again and
1695 add all tests to the stylesheet compilation. Using the DTD provided in the
1696 appendix and making direct checks using the libxml validation API sounds a
1697 good idea too (though one should take care of not raising errors for
1698 elements/attributes in different namespaces).</p>
1700 <p>Double check all the places where the stylesheet compiled form might be
1701 modified at run time (extra removal of blanks nodes, hint on the
1706 <h2><a name="Extensions">Writing extensions</a></h2>
1708 <h3>Table of content</h3>
1710 <li><a href="extensions.html#Introducti">Introduction</a></li>
1711 <li><a href="extensions.html#Basics">Basics</a></li>
1712 <li><a href="extensions.html#Keep">Extension modules</a></li>
1713 <li><a href="extensions.html#Registerin">Registering a module</a></li>
1714 <li><a href="extensions.html#module">Loading a module</a></li>
1715 <li><a href="extensions.html#Registerin1">Registering an extension
1717 <li><a href="extensions.html#Implementi">Implementing an extension
1719 <li><a href="extensions.html#Examples">Examples for extension
1721 <li><a href="extensions.html#Registerin2">Registering an extension
1723 <li><a href="extensions.html#Implementi1">Implementing an extension
1725 <li><a href="extensions.html#Example">Example for extension
1727 <li><a href="extensions.html#shutdown">The shutdown of a module</a></li>
1728 <li><a href="extensions.html#Future">Future work</a></li>
1731 <h3><a name="Introducti1">Introduction</a></h3>
1733 <p>This document describes the work needed to write extensions to the
1734 standard XSLT library for use with <a
1735 href="http://xmlsoft.org/XSLT/">libxslt</a>, the <a
1736 href="http://www.w3.org/TR/xslt">XSLT</a> C library developed for the <a
1737 href="http://www.gnome.org/">Gnome</a> project.</p>
1739 <p>Before starting reading this document it is highly recommended to get
1740 familiar with <a href="internals.html">the libxslt internals</a>.</p>
1742 <p>Note: this documentation is by definition incomplete and I am not good at
1743 spelling, grammar, so patches and suggestions are <a
1744 href="mailto:veillard@redhat.com">really welcome</a>.</p>
1746 <h3><a name="Basics">Basics</a></h3>
1748 <p>The <a href="http://www.w3.org/TR/xslt">XSLT specification</a> provides
1749 two <a href="http://www.w3.org/TR/xslt">ways to extend an XSLT engine</a>:</p>
1751 <li>providing <a href="http://www.w3.org/TR/xslt">new extension
1752 functions</a> which can be called from XPath expressions</li>
1753 <li>providing <a href="http://www.w3.org/TR/xslt">new extension
1754 elements</a> which can be inserted in stylesheets</li>
1757 <p>In both cases the extensions need to be associated to a new namespace,
1758 i.e. an URI used as the name for the extension's namespace (there is no need
1759 to have a resource there for this to work).</p>
1761 <p>libxslt provides a few extensions itself, either in libxslt namespace
1762 "http://xmlsoft.org/XSLT/" or in other namespace for well known extensions
1763 provided by other XSLT processors like Saxon, Xalan or XT.</p>
1765 <h3><a name="Keep">Extension modules</a></h3>
1767 <p>Since extensions are bound to a namespace name, usually sets of extensions
1768 coming from a given source are using the same namespace name defining in
1769 practice a group of extensions providing elements, functions or both. From
1770 libxslt point of view those are considered as an "extension module", and most
1771 of the APIs work at a module point of view.</p>
1773 <p>Registration of new functions or elements are bound to the activation of
1774 the module, this is currently done by declaring the namespace as an extension
1775 by using the attribute <code>extension-element-prefixes</code> on the
1776 <code><a href="http://www.w3.org/TR/xslt">xsl:stylesheet</a></code>
1779 <p>And extension module is defined by 3 objects:</p>
1781 <li>the namespace name associated</li>
1782 <li>an initialization function</li>
1783 <li>a shutdown function</li>
1786 <h3><a name="Registerin">Registering a module</a></h3>
1788 <p>Currently a libxslt module has to be compiled within the application using
1789 libxslt, there is no code to load dynamically shared libraries associated to
1790 namespace (this may be added but is likely to become a portability
1793 <p>So the current way to register a module is to link the code implementing
1794 it with the application and to call a registration function:</p>
1795 <pre>int xsltRegisterExtModule(const xmlChar *URI,
1796 xsltExtInitFunction initFunc,
1797 xsltExtShutdownFunction shutdownFunc);</pre>
1799 <p>The associated header is read by:</p>
1800 <pre>#include<libxslt/extensions.h></pre>
1802 <p>which also defines the type for the initialization and shutdown
1805 <h3><a name="module">Loading a module</a></h3>
1807 <p>Once the module URI has been registered and if the XSLT processor detects
1808 that a given stylesheet needs the functionalities of an extended module, this
1809 one is initialized.</p>
1811 <p>The xsltExtInitFunction type defines the interface for an initialization
1814 * xsltExtInitFunction:
1815 * @ctxt: an XSLT transformation context
1816 * @URI: the namespace URI for the extension
1818 * A function called at initialization time of an XSLT
1821 * Returns a pointer to the module specific data for this
1824 typedef void *(*xsltExtInitFunction)(xsltTransformContextPtr ctxt,
1825 const xmlChar *URI);</pre>
1827 <p>There are 3 things to notice:</p>
1829 <li>the function gets passed the namespace name URI as an argument, this
1830 allow a single function to provide the initialization for multiple
1831 logical modules</li>
1832 <li>it also gets passed a transformation context, the initialization is
1833 done at run time before any processing occurs on the stylesheet but it
1834 will be invoked separately each time for each transformation</li>
1835 <li>it returns a pointer, this can be used to store module specific
1836 informations which can be retrieved later when a function or an element
1837 from the extension are used, an obvious example is a connection to a
1838 database which should be kept and reused along the transformation. NULL
1839 is a perfectly valid return, there is no way to indicate a failure at
1843 <p>What this function is expected to do is:</p>
1845 <li>prepare the context for this module (like opening the database
1847 <li>register the extensions specific to this module</li>
1850 <h3><a name="Registerin1">Registering an extension function</a></h3>
1852 <p>There is a single call to do this registration:</p>
1853 <pre>int xsltRegisterExtFunction(xsltTransformContextPtr ctxt,
1854 const xmlChar *name,
1856 xmlXPathEvalFunc function);</pre>
1858 <p>The registration is bound to a single transformation instance referred by
1859 ctxt, name is the UTF8 encoded name for the NCName of the function, and URI
1860 is the namespace name for the extension (no checking is done, a module could
1861 register functions or elements from a different namespace, but it is not
1864 <h3><a name="Implementi">Implementing an extension function</a></h3>
1866 <p>The implementation of the function must have the signature of a libxml
1870 * @ctxt: an XPath parser context
1871 * @nargs: the number of arguments passed to the function
1873 * an XPath evaluation function, the parameters are on the
1874 * XPath context stack
1877 typedef void (*xmlXPathEvalFunc)(xmlXPathParserContextPtr ctxt,
1880 <p>The context passed to an XPath function is not an XSLT context but an <a
1881 href="internals.html#XPath1">XPath context</a>. However it is possible to
1882 find one from the other:</p>
1884 <li>The function xsltXPathGetTransformContext provide this lookup facility:
1885 <pre>xsltTransformContextPtr
1886 xsltXPathGetTransformContext
1887 (xmlXPathParserContextPtr ctxt);</pre>
1889 <li>The <code>xmlXPathContextPtr</code> associated to an
1890 <code>xsltTransformContext</code> is stored in the <code>xpathCtxt</code>
1894 <p>The first thing an extension function may want to do is to check the
1895 arguments passed on the stack, the <code>nargs</code> will precise how many
1896 of them were provided on the XPath expression. The macros valuePop will
1897 extract them from the XPath stack:</p>
1898 <pre>#include <libxml/xpath.h>
1899 #include <libxml/xpathInternals.h>
1901 xmlXPathObjectPtr obj = valuePop(ctxt); </pre>
1903 <p>Note that <code>ctxt</code> is the XPath context not the XSLT one. It is
1904 then possible to examine the content of the value. Check <a
1905 href="internals.html#Descriptio">the description of XPath objects</a> if
1906 necessary. The following is a common sequcnce checking whether the argument
1907 passed is a string and converting it using the built-in XPath
1908 <code>string()</code> function if this is not the case:</p>
1909 <pre>if (obj->type != XPATH_STRING) {
1910 valuePush(ctxt, obj);
1911 xmlXPathStringFunction(ctxt, 1);
1912 obj = valuePop(ctxt);
1915 <p>Most common XPath functions are available directly at the C level and are
1916 exported either in <code><libxml/xpath.h></code> or in
1917 <code><libxml/xpathInternals.h></code>.</p>
1919 <p>The extension function may also need to retrieve the data associated to
1920 this module instance (the database connection in the previous example) this
1921 can be done using the xsltGetExtData:</p>
1922 <pre>void * xsltGetExtData(xsltTransformContextPtr ctxt,
1923 const xmlChar *URI);</pre>
1925 <p>again the URI to be provided is the one used which was used when
1926 registering the module.</p>
1928 <p>Once the function finishes, don't forget to:</p>
1930 <li>push the return value on the stack using <code>valuePush(ctxt,
1932 <li>deallocate the parameters passed to the function using
1933 <code>xmlXPathFreeObject(obj)</code></li>
1936 <h3><a name="Examples">Examples for extension functions</a></h3>
1938 <p>The module libxslt/functions.c containsthe sources of the XSLT built-in
1939 functions, including document(), key(), generate-id(), etc. as well as a full
1940 example module at the end. Here is the test function implementation for the
1941 libxslt:test function:</p>
1943 * xsltExtFunctionTest:
1944 * @ctxt: the XPath Parser context
1945 * @nargs: the number of arguments
1947 * function libxslt:test() for testing the extensions support.
1950 xsltExtFunctionTest(xmlXPathParserContextPtr ctxt, int nargs)
1952 xsltTransformContextPtr tctxt;
1955 tctxt = xsltXPathGetTransformContext(ctxt);
1956 if (tctxt == NULL) {
1957 xsltGenericError(xsltGenericErrorContext,
1958 "xsltExtFunctionTest: failed to get the transformation context\n");
1961 data = xsltGetExtData(tctxt, (const xmlChar *) XSLT_DEFAULT_URL);
1963 xsltGenericError(xsltGenericErrorContext,
1964 "xsltExtFunctionTest: failed to get module data\n");
1967 #ifdef WITH_XSLT_DEBUG_FUNCTION
1968 xsltGenericDebug(xsltGenericDebugContext,
1969 "libxslt:test() called with %d args\n", nargs);
1973 <h3><a name="Registerin2">Registering an extension element</a></h3>
1975 <p>There is a single call to do this registration:</p>
1976 <pre>int xsltRegisterExtElement(xsltTransformContextPtr ctxt,
1977 const xmlChar *name,
1979 xsltTransformFunction function);</pre>
1981 <p>It is similar to the mechanism used to register an extension function,
1982 except that the signature of an extension element implementation is
1985 <p>The registration is bound to a single transformation instance referred by
1986 ctxt, name is the UTF8 encoded name for the NCName of the element, and URI is
1987 the namespace name for the extension (no checking is done, a module could
1988 register elements for a different namespace, but it is not recommended).</p>
1990 <h3><a name="Implementi1">Implementing an extension element</a></h3>
1992 <p>The implementation of the element must have the signature of an XSLT
1993 transformation function:</p>
1995 * xsltTransformFunction:
1996 * @ctxt: the XSLT transformation context
1997 * @node: the input node
1998 * @inst: the stylesheet node
1999 * @comp: the compiled information from the stylesheet
2001 * signature of the function associated to elements part of the
2002 * stylesheet language like xsl:if or xsl:apply-templates.
2004 typedef void (*xsltTransformFunction)
2005 (xsltTransformContextPtr ctxt,
2008 xsltStylePreCompPtr comp);</pre>
2010 <p>The first argument is the XSLT transformation context. The second and
2011 third arguments are xmlNodePtr i.e. internal memory <a
2012 href="internals.html#libxml">representation of XML nodes</a>. They are
2013 respectively <code>node</code> from the the input document being transformed
2014 by the stylesheet and <code>inst</code> the extension element in the
2015 stylesheet. The last argument is <code>comp</code> a pointer to a precompiled
2016 representation of <code>inst</code> but usually for extension function this
2017 value is <code>NULL</code> by default (it could be added and associated to
2018 the instruction in <code>inst->_private</code>).</p>
2020 <p>The same functions are available from a function implementing an extension
2021 element as in an extension function, including
2022 <code>xsltGetExtData()</code>.</p>
2024 <p>The goal of extension element being usually to enrich the generated
2025 output, it is expected that they will grow the currently generated output
2026 tree, this can be done by grabbing ctxt->insert which is the current
2027 libxml node being generated (Note this can also be the intermediate value
2028 tree being built for example to initialize a variable, the processing should
2029 be similar). The functions for libxml tree manipulation from <a
2030 href="http://xmlsoft.org/html/libxml-tree.html"><libxml/tree.h></a> can
2031 be employed to extend or modify the tree, but it is required to preserve the
2032 insertion node and its ancestors since there is existing pointers to those
2033 elements still in use in the XSLT template execution stack.</p>
2035 <h3><a name="Example">Example for extension elements</a></h3>
2037 <p>The module libxslt/transform.c containsthe sources of the XSLT built-in
2038 elements, including xsl:element, xsl:attribute, xsl:if, etc. There is a small
2039 but full example in functions.c providing the implementation for the
2040 libxslt:test element, it will output a comment in the result tree:</p>
2042 * xsltExtElementTest:
2043 * @ctxt: an XSLT processing context
2044 * @node: The current node
2045 * @inst: the instruction in the stylesheet
2046 * @comp: precomputed informations
2048 * Process a libxslt:test node
2051 xsltExtElementTest(xsltTransformContextPtr ctxt, xmlNodePtr node,
2053 xsltStylePreCompPtr comp)
2058 xsltGenericError(xsltGenericErrorContext,
2059 "xsltExtElementTest: no transformation context\n");
2063 xsltGenericError(xsltGenericErrorContext,
2064 "xsltExtElementTest: no current node\n");
2068 xsltGenericError(xsltGenericErrorContext,
2069 "xsltExtElementTest: no instruction\n");
2072 if (ctxt->insert == NULL) {
2073 xsltGenericError(xsltGenericErrorContext,
2074 "xsltExtElementTest: no insertion point\n");
2078 xmlNewComment((const xmlChar *)
2079 "libxslt:test element test worked");
2080 xmlAddChild(ctxt->insert, comment);
2083 <h3><a name="shutdown">The shutdown of a module</a></h3>
2085 <p>When the XSLT processor ends a transformation, the shutdown function (if
2086 it exists) of all the modules initialized are called.The
2087 xsltExtShutdownFunction type defines the interface for a shutdown
2090 * xsltExtShutdownFunction:
2091 * @ctxt: an XSLT transformation context
2092 * @URI: the namespace URI for the extension
2093 * @data: the data associated to this module
2095 * A function called at shutdown time of an XSLT extension module
2097 typedef void (*xsltExtShutdownFunction) (xsltTransformContextPtr ctxt,
2101 <p>this is really similar to a module initialization function except a third
2102 argument is passed, it's the value that was returned by the initialization
2103 function. This allow to deallocate resources from the module for example
2104 close the connection to the database to keep the same example.</p>
2106 <h3><a name="Future">Future work</a></h3>
2108 <p>Well some of the pieces missing:</p>
2110 <li>a way to load shared libraries to instanciate new modules</li>
2111 <li>a better detection of extension function usage and their registration
2112 without having to use the extension prefix which ought to be reserved to
2113 element extensions.</li>
2114 <li>more examples</li>
2115 <li>implementations of the <a href="http://www.exslt.org/">EXSLT</a> common
2116 extension libraries, Thomas Broyer nearly finished implementing them.</li>
2121 <h2><a name="Contributi">Contributions</a></h2>
2123 <li>Bjorn Reese is the author of the number support and worked on the
2124 XSLTMark support</li>
2125 <li>William Brack was an early adopted, contributed a number of patches and
2126 spent quite some time debugging non-trivial problems in early versions of
2128 <li><a href="mailto:igor@zlatkovic.com">Igor Zlatkovic</a> is now the
2129 maintainer of the Windows port, <a
2130 href="http://www.zlatkovic.com/projects/libxml/index.html">he provides
2132 <li>Thomas Broyer provided a lot of suggestions, and drafted most of the
2134 <li>John Fleck maintains <a href="tutorial/libxslttutorial.html">a tutorial
2135 for libxslt</a></li>
2137 href="http://mail.gnome.org/archives/xml/2001-March/msg00014.html">Matt
2138 Sergeant</a> developed <a
2139 href="http://axkit.org/download/">XML::LibXSLT</a>, a perl wrapper for
2140 libxml2/libxslt as part of the <a href="http://axkit.com/">AxKit XML
2141 application server</a></li>
2142 <li>there is a module for <a
2143 href="http://acs-misc.sourceforge.net/nsxml.html">libxml/libxslt support
2144 in OpenNSD/AOLServer</a></li>
2145 <li><a href="mailto:dkuhlman@cutter.rexx.com">Dave Kuhlman</a> provides
2146 libxml/libxslt <a href="http://www.rexx.com/~dkuhlman">wrappers for
2148 <li><a href="mailto:Steve.Ball@zveno.com">Steve Ball</a>, <a
2149 href="http://www.zveno.com/">Zveno</a> and contributors maintain <a
2150 href="http://tclxml.sourceforge.net/">tcl bindings for libxml2 and
2151 libxslt</a>, as well as <a
2152 href="http://tclxml.sf.net/tkxmllint.html">tkxmllint</a> a GUI for
2153 xmllint and <a href="http://tclxml.sf.net/tkxsltproc.html">tkxsltproc</a>
2154 a GUI for xsltproc.</li>
2155 <li>If you want to use libxslt in a Mac OS X/Cocoa or Objective-C
2156 framework, Marc Liyanage provides <a
2157 href="http://www.entropy.ch/software/macosx/#testxslt">an application
2158 TestXSLT for XSLT and XML editing</a> including wrapper classes for the
2159 XML parser and XSLT processor.</li>
2164 <p><a href="mailto:daniel@veillard.com">Daniel Veillard</a></p>