  
  
  
The XML C parser and toolkit of Gnome
Note: this is the flat content of the index.htmlweb
site
libxml, a.k.a. gnome-xml
"Programming
with libxml2 is like the thrilling embrace of an exotic stranger." 
http://diveintomark.org/archives/2004/02/18/libxml2Mark
Pilgrim
Libxml2 is the XML C parser and toolkit developed for the Gnome project
(but usable outside of the Gnome platform), it is free software available
under the 
http://www.opensource.org/licenses/mit-license.htmlMIT
License
. XML itself is a metalanguage to design markup languages, i.e.
text language where semantic and structure are added to the content using
extra "markup" information enclosed between angle brackets. HTML is the most
well-known markup language. Though the library is written in C 
python.htmla variety of language bindings  make it available in
other environments.
Libxml2 is known to be very portable, the library should build and work
without serious troubles on a variety of systems (Linux, Unix, Windows,
CygWin, MacOS, MacOS X, RISC Os, OS/2, VMS, QNX, MVS, ...)
Libxml2 implements a number of existing standards related to markup
languages:
  
the XML standard: http://www.w3.org/TR/REC-xmlhttp://www.w3.org/TR/REC-xml   
Namespaces in XML: http://www.w3.org/TR/REC-xml-names/http://www.w3.org/TR/REC-xml-names/   
XML Base: http://www.w3.org/TR/xmlbase/http://www.w3.org/TR/xmlbase/   
http://www.cis.ohio-state.edu/rfc/rfc2396.txtRFC 2396  :
    Uniform Resource Identifiers 
http://www.ietf.org/rfc/rfc2396.txthttp://www.ietf.org/rfc/rfc2396.txt   
XML Path Language (XPath) 1.0: http://www.w3.org/TR/xpathhttp://www.w3.org/TR/xpath   
HTML4 parser: http://www.w3.org/TR/html401/http://www.w3.org/TR/html401/   
XML Pointer Language (XPointer) Version 1.0: http://www.w3.org/TR/xptrhttp://www.w3.org/TR/xptr   
XML Inclusions (XInclude) Version 1.0: http://www.w3.org/TR/xinclude/http://www.w3.org/TR/xinclude/   
ISO-8859-x encodings, as well as http://www.cis.ohio-state.edu/rfc/rfc2044.txtrfc2044  [UTF-8]
    and 
http://www.cis.ohio-state.edu/rfc/rfc2781.txtrfc2781     [UTF-16] Unicode encodings, and more if using iconv support
  
part of SGML Open Technical Resolution TR9401:1997  
XML Catalogs Working Draft 06 August 2001: http://www.oasis-open.org/committees/entity/spec-2001-08-06.htmlhttp://www.oasis-open.org/committees/entity/spec-2001-08-06.html   
Canonical XML Version 1.0: http://www.w3.org/TR/xml-c14nhttp://www.w3.org/TR/xml-c14n     and the Exclusive XML Canonicalization CR draft 
http://www.w3.org/TR/xml-exc-c14nhttp://www.w3.org/TR/xml-exc-c14n   
Relax NG, ISO/IEC 19757-2:2003, http://www.oasis-open.org/committees/relax-ng/spec-20011203.htmlhttp://www.oasis-open.org/committees/relax-ng/spec-20011203.html   
W3C XML Schemas Part 2: Datatypes http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/REC 02 May
    2001
  
W3C http://www.w3.org/TR/xml-id/xml:id  Working Draft 7
    April 2004
In most cases libxml2 tries to implement the specifications in a
relatively strictly compliant way. As of release 2.4.16, libxml2 passed all
1800+ tests from the 
http://www.oasis-open.org/committees/xml-conformance/OASIS XML Tests
Suite
.
To some extent libxml2 provides support for the following additional
specifications but doesn't claim to implement them completely:
  
Document Object Model (DOM) http://www.w3.org/TR/DOM-Level-2-Core/http://www.w3.org/TR/DOM-Level-2-Core/     the document model, but it doesn't implement the API itself, gdome2 does
    this on top of libxml2
  
http://www.cis.ohio-state.edu/rfc/rfc959.txtRFC 959  :
    libxml2 implements a basic FTP client code
  
http://www.cis.ohio-state.edu/rfc/rfc1945.txtRFC 1945  :
    HTTP/1.0, again a basic HTTP client code
  
SAX: a SAX2 like interface and a minimal SAX1 implementation compatible
    with early expat versions
A partial implementation of http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/XML Schemas Part
1: Structure
 is being worked on but it would be far too early to make any
conformance statement about it at the moment.
Separate documents:
  
http://xmlsoft.org/XSLT/the libxslt page  providing an
    implementation of XSLT 1.0 and common extensions like EXSLT for
  libxml2
  
http://www.cs.unibo.it/~casarini/gdome2/the gdome2 page     : a standard DOM2 implementation for libxml2
  
http://www.aleksey.com/xmlsec/the XMLSec page : an
    implementation of 
http://www.w3.org/TR/xmldsig-core/W3C XML
    Digital Signature
 for libxml2  
also check the related links section below for more related and active
    projects.
Logo designed by mailto:liyanage@access.chMarc Liyanage .
Introduction 
This document describes libxml, the http://www.w3.org/XML/XML  C parser and toolkit developed for the
http://www.gnome.org/Gnome  project. http://www.w3.org/XML/XML is a standard  for building tag-based
structured documents/data.
Here are some key points about libxml:
  
Libxml2 exports Push (progressive) and Pull (blocking) type parser
    interfaces for both XML and HTML.
  
Libxml2 can do DTD validation at parse time, using a parsed document
    instance, or with an arbitrary DTD.
  
Libxml2 includes complete http://www.w3.org/TR/xpathXPath , http://www.w3.org/TR/xptrXPointer  and http://www.w3.org/TR/xincludeXInclude  implementations.  
It is written in plain C, making as few assumptions as possible, and
    sticking closely to ANSI C/POSIX for easy embedding. Works on
    Linux/Unix/Windows, ported to a number of other platforms.
  
Basic support for HTTP and FTP client allowing applications to fetch
    remote resources.
  
The design is modular, most of the extensions can be compiled out.  
The internal document representation is as close as possible to the http://www.w3.org/DOM/DOM  interfaces.  
Libxml2 also has a http://www.megginson.com/SAX/index.htmlSAX like interface ;
    the interface is designed to be compatible with 
http://www.jclark.com/xml/expat.htmlExpat .  
This library is released under the http://www.opensource.org/licenses/mit-license.htmlMIT
    License
. See the Copyright file in the distribution for the precise
    wording.
Warning: unless you are forced to because your application links with a
Gnome-1.X library requiring it,  
Do Not Use libxml1, use
libxml2
FAQ 
Table of Contents:
  
FAQ.html#LicenseLicense(s)   
FAQ.html#InstallatiInstallation   
FAQ.html#CompilatioCompilation   
FAQ.html#DeveloperDeveloper corner License (s)
  
Licensing Terms for libxml    
libxml2 is released under the http://www.opensource.org/licenses/mit-license.htmlMIT
    License
; see the file Copyright in the distribution for the precise
    wording
  
  
Can I embed libxml2 in a proprietary application ?    
Yes. The MIT License allows you to keep proprietary the changes you
    made to libxml, but it would be graceful to send-back bug fixes and
    improvements as patches for possible incorporation in the main
    development tree.
  
Installation 
  
Do Not Use
    libxml1
, use libxml2  
Where can I get libxml ?
    
The original distribution comes from ftp://rpmfind.net/pub/libxml/rpmfind.net  or ftp://ftp.gnome.org/pub/GNOME/sources/libxml2/2.6/gnome.org 
    
Most Linux and BSD distributions include libxml, this is probably the
    safer way for end-users to use libxml.
    
David Doolin provides precompiled Windows versions at http://www.ce.berkeley.edu/~doolin/code/libxmlwin32/         http://www.ce.berkeley.edu/~doolin/code/libxmlwin32/ 
  
  
I see libxml and libxml2 releases, which one should I install ?    
      
If you are not constrained by backward compatibility issues with
        existing applications, install libxml2 only
      
If you are not doing development, you can safely install both.
        Usually the packages 
http://rpmfind.net/linux/RPM/libxml.htmllibxml  and http://rpmfind.net/linux/RPM/libxml2.htmllibxml2  are
        compatible (this is not the case for development packages).
      
If you are a developer and your system provides separate packaging
        for shared libraries and the development components, it is possible
        to install libxml and libxml2, and also 
http://rpmfind.net/linux/RPM/libxml-devel.htmllibxml-devel         and 
http://rpmfind.net/linux/RPM/libxml2-devel.htmllibxml2-devel         too for libxml2 >= 2.3.0
      
If you are developing a new application, please develop against
        libxml2(-devel)
    
  
  
I can't install the libxml package, it conflicts with libxml0    
You probably have an old libxml0 package used to provide the shared
    library for libxml.so.0, you can probably safely remove it. The libxml
    packages provided on 
ftp://rpmfind.net/pub/libxml/rpmfind.net  provide
    libxml.so.0
  
  
I can't install the libxml(2) RPM package due to failed
    dependencies
    
The most generic solution is to re-fetch the latest src.rpm , and
    rebuild it locally with
    
rpm --rebuild libxml(2)-xxx.src.rpm.
    
If everything goes well it will generate two binary rpm packages (one
    providing the shared libs and xmllint, and the other one, the -devel
    package, providing includes, static libraries and scripts needed to build
    applications with libxml(2)) that you can install locally.
  
Compilation 
  
What is the process to compile libxml2 ?    
As most UNIX libraries libxml2 follows the "standard":
    
gunzip -c xxx.tar.gz | tar xvf -
    
cd libxml-xxxx
    
./configure --help
    
to see the options, then the compilation/installation proper
    
./configure [possible options]
    
make
    
make install
    
At that point you may have to rerun ldconfig or a similar utility to
    update your list of installed shared libs.
  
  
What other libraries are needed to compile/install libxml2 ?    
Libxml2 does not require any other library, the normal C ANSI API
    should be sufficient (please report any violation to this rule you may
    find).
    
However if found at configuration time libxml2 will detect and use the
    following libs:
    
      
http://www.info-zip.org/pub/infozip/zlib/libz  : a
        highly portable and available widely compression library.
      
iconv: a powerful character encoding conversion library. It is
        included by default in recent glibc libraries, so it doesn't need to
        be installed specifically on Linux. It now seems a 
http://www.opennc.org/onlinepubs/7908799/xsh/iconv.htmlpart
        of the official UNIX
 specification. Here is one http://www.gnu.org/software/libiconv/implementation of the
        library
 which source can be found ftp://ftp.ilog.fr/pub/Users/haible/gnu/here .    
  
  
Make check fails on some platforms    
Sometimes the regression tests' results don't completely match the
    value produced by the parser, and the makefile uses diff to print the
    delta. On some platforms the diff return breaks the compilation process;
    if the diff is small this is probably not a serious problem.
    
Sometimes (especially on Solaris) make checks fail due to limitations
    in make. Try using GNU-make instead.
  
  
I use the CVS version and there is no configure script    
The configure script (and other Makefiles) are generated. Use the
    autogen.sh script to regenerate the configure script and Makefiles,
    like:
    
./autogen.sh --prefix=/usr --disable-shared
  
  
I have troubles when running make tests with gcc-3.0    
It seems the initial release of gcc-3.0 has a problem with the
    optimizer which miscompiles the URI module. Please use another
    compiler.
  
Developer  corner
  
Troubles compiling or linking programs using libxml2    
Usually the problem comes from the fact that the compiler doesn't get
    the right compilation or linking flags. There is a small shell script
    
xml2-config which is installed as part of libxml2 usual
    install process which provides those flags. Use
    
xml2-config --cflags
    
to get the compilation flags and
    
xml2-config --libs
    
to get the linker flags. Usually this is done directly from the
    Makefile as:
    
CFLAGS=`xml2-config --cflags`
    
LIBS=`xml2-config --libs`
  
  
I want to install my own copy of libxml2 in my home directory and
    link my programs against it, but it doesn't work
    
There are many different ways to accomplish this.  Here is one way to
    do this under Linux.  Suppose your home directory is 
/home/user.
    
Then:
    
      
Create a subdirectory, let's call it myxml      
unpack the libxml2 distribution into that subdirectory      
chdir into the unpacked distribution
        (
/home/user/myxml/libxml2 )      
configure the library using the "--prefix" switch,
        specifying an installation subdirectory in
        
/home/user/myxml, e.g.
        
./configure --prefix /home/user/myxml/xmlinst {other
        configuration options}
      
      
now run make followed by make install      
At this point, the installation subdirectory contains the complete
        "private" include files, library files and binary program files (e.g.
        xmllint), located in
        
/home/user/myxml/xmlinst/lib,
        /home/user/myxml/xmlinst/include 
 and         /home/user/myxml/xmlinst/bin
        respectively.
      
In order to use this "private" library, you should first add it to
        the beginning of your default PATH (so that your own private program
        files such as xmllint will be used instead of the normal system
        ones).  To do this, the Bash command would be
        
export PATH=/home/user/myxml/xmlinst/bin:$PATH
      
      
Now suppose you have a program test1.c that you would
        like to compile with your "private" library.  Simply compile it using
        the command
        
gcc `xml2-config --cflags --libs` -o test test.c
        Note that, because your PATH has been set with 
        /home/user/myxml/xmlinst/bin
 at the beginning, the xml2-config
        program which you just installed will be used instead of the system
        default one, and this will 
automatically get the correct
        libraries linked with your program.
    
  
  
  
xmlDocDump() generates output on one line.    
Libxml2 will not invent spaces in the content of a
    document since 
all spaces in the content of a document are
    significant
. If you build a tree from the API and want
    indentation:
    
      
the correct way is to generate those yourself too.      
the dangerous way is to ask libxml2 to add those blanks to your
        content 
modifying the content of your document in the
        process
. The result may not be what you expect. There is
        
NO way to guarantee that such a modification won't
        affect other parts of the content of your document. See 
http://xmlsoft.org/html/libxml-parser.html#xmlKeepBlanksDefaultxmlKeepBlanksDefault
        ()
 and http://xmlsoft.org/html/libxml-tree.html#xmlSaveFormatFilexmlSaveFormatFile
        ()
    
  
  
Extra nodes in the document:
    
For a XML file as below:
    
<?xml version="1.0"?>
<PLAN xmlns="http://www.argus.ca/autotest/1.0/">
<NODE CommFlag="0"/>
<NODE CommFlag="1"/>
</PLAN>
    
after parsing it with the function
    pxmlDoc=xmlParseFile(...);
    
I want to the get the content of the first node (node with the
    CommFlag="0")
    
so I did it as following;
    
xmlNodePtr pnode;
pnode=pxmlDoc->children->children;
    
but it does not work. If I change it to
    
pnode=pxmlDoc->children->children->next;    
then it works.  Can someone explain it to me.
    
    
In XML all characters in the content of the document are significant
    
including blanks and formatting line breaks.
    
The extra nodes you are wondering about are just that, text nodes with
    the formatting spaces which are part of the document but that people tend
    to forget. There is a function 
http://xmlsoft.org/html/libxml-parser.htmlxmlKeepBlanksDefault
    ()
  to remove those at parse time, but that's an heuristic, and its
    use should be limited to cases where you are certain there is no
    mixed-content in the document.
  
  
I get compilation errors of existing code like when accessing
    
root or child fields of nodes.    
You are compiling code developed for libxml version 1 and using a
    libxml2 development environment. Either switch back to libxml v1 devel or
    even better fix the code to compile with libxml2 (or both) by 
upgrade.htmlfollowing the instructions .
  
  
I get compilation errors about non existing
    
xmlRootNode or xmlChildrenNode    fields.
    
The source code you are using has been upgrade.htmlupgraded  to be able to compile with both libxml
    and libxml2, but you need to install a more recent version:
    libxml(-devel) >= 1.8.8 or libxml2(-devel) >= 2.1.0
  
  
XPath implementation looks seriously broken    
XPath implementation prior to 2.3.0 was really incomplete. Upgrade to
    a recent version, there are no known bugs in the current version.
  
  
The example provided in the web page does not compile.    
It's hard to maintain the documentation in sync with the code
    <grin/> ...
    
Check the previous points 1/ and 2/ raised before, and please send
    patches.
  
  
Where can I get more examples and information than provided on the
    web page?
    
Ideally a libxml2 book would be nice. I have no such plan ... But you
    can:
    
      
check more deeply the html/libxml-lib.htmlexisting
        generated doc
      
have a look at examples/index.htmlthe set of
        examples
.      
look for examples of use for libxml2 function using the Gnome code.
        For example the following will query the full Gnome CVS base for the
        use of the 
xmlAddChild() function:
        
http://cvs.gnome.org/lxr/search?string=xmlAddChildhttp://cvs.gnome.org/lxr/search?string=xmlAddChild 
        
This may be slow, a large hardware donation to the gnome project
        could cure this :-)
      
      
http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&dir=gnome-xmlBrowse
        the libxml2 source
 , I try to write code as clean and documented
        as possible, so looking at it may be helpful. In particular the code
        of xmllint.c and of the various testXXX.c test programs should
        provide good examples of how to do things with the library.
    
  
  
What about C++ ?
    
libxml2 is written in pure C in order to allow easy reuse on a number
    of platforms, including embedded systems. I don't intend to convert to
    C++.
    
There is however a C++ wrapper which may fulfill your needs:
    
      
by Ari Johnson <ari@btigate.com>:
        
Website: http://libxmlplusplus.sourceforge.net/http://libxmlplusplus.sourceforge.net/ 
        
Download: http://sourceforge.net/project/showfiles.php?group_id=12999http://sourceforge.net/project/showfiles.php?group_id=12999 
      
      
    
  
  
How to validate a document a posteriori ?
    
It is possible to validate documents which had not been validated at
    initial parsing time or documents which have been built from scratch
    using the API. Use the 
http://xmlsoft.org/html/libxml-valid.html#xmlValidateDtdxmlValidateDtd()     function. It is also possible to simply add a DTD to an existing
    document:
    
xmlDocPtr doc; /* your existing document */
xmlDtdPtr dtd = xmlParseDTD(NULL, filename_of_dtd); /* parse the DTD */
        dtd->name = xmlStrDup((xmlChar*)"root_name"); /* use the given root */
        doc->intSubset = dtd;
        if (doc->children == NULL) xmlAddChild((xmlNodePtr)doc, (xmlNodePtr)dtd);
        else xmlAddPrevSibling(doc->children, (xmlNodePtr)dtd);
          
  
  
So what is this funky "xmlChar" used all the time?
    
It is a null terminated sequence of utf-8 characters. And only utf-8!
    You need to convert strings encoded in different ways to utf-8 before
    passing them to the API.  This can be accomplished with the iconv library
    for instance.
  
  
etc ...
Developer Menu 
There are several on-line resources related to using libxml:
  
Use the search.phpsearch engine  to look up
  information.
  
Check the FAQ.htmlFAQ.   
Check the http://xmlsoft.org/html/libxml-lib.htmlextensive
    documentation
 automatically extracted from code comments.  
Look at the documentation about encoding.htmllibxml
    internationalization support
.  
This page provides a global overview and example.htmlsome
    examples
 on how to use libxml.  
examples/index.htmlCode examples   
John Fleck's libxml2 tutorial: tutorial/index.htmlhtml     or 
tutorial/xmltutorial.pdfpdf .  
If you need to parse large files, check the xmlreader.htmlxmlReader  API tutorial  
mailto:james@daa.com.auJames Henstridge  wrote http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.htmlsome nice
    documentation
 explaining how to use the libxml SAX interface.  
George Lebl wrote http://www-106.ibm.com/developerworks/library/l-gnome3/an article
    for IBM developerWorks
 about using libxml.  
Check http://cvs.gnome.org/lxr/source/gnome-xml/TODOthe TODO
    file
.  
Read the upgrade.html1.x to 2.x upgrade path     description. If you are starting a new project using libxml you should
    really use the 2.x version.
  
And don't forget to look at the http://mail.gnome.org/archives/xml/mailing-list archive . Reporting bugs and getting help 
Well, bugs or missing features are always possible, and I will make a
point of fixing them in a timely fashion. The best way to report a bug is to
use the 
http://bugzilla.gnome.org/buglist.cgi?product=libxml2Gnome
bug tracking database
 (make sure to use the "libxml2" module name). I
look at reports there regularly and it's good to have a reminder when a bug
is still open. Be sure to specify that the bug is for the package libxml2.
For small problems you can try to get help on IRC, the #xml channel on
irc.gnome.org (port 6667) usually have a few person subscribed which may help
(but there is no garantee and if a real issue is raised it should go on the
mailing-list for archival).
There is also a mailing-list mailto:xml@gnome.orgxml@gnome.org  for libxml, with an  http://mail.gnome.org/archives/xml/on-line archive  ( http://xmlsoft.org/messagesold ). To subscribe to this list,
please visit the 
http://mail.gnome.org/mailman/listinfo/xmlassociated Web  page and
follow the instructions. 
Do not send code, I won't debug it(but patches are really appreciated!).
Please note that with the current amount of virus and SPAM, sending mail
to the list without being subscribed won't work. There is *far too many
bounces* (in the order of a thousand a day !) I cannot approve them manually
anymore. If your mail to the list bounced waiting for administrator approval,
it is LOST ! Repost it and fix the problem triggering the error.
Check the following before
posting
:
  
Read the FAQ.htmlFAQ  and search.phpuse the
    search engine
 to get information related to your problem.  
Make sure you are ftp://xmlsoft.org/using a recent
    version
, and that the problem still shows up in a recent version.  
Check the http://mail.gnome.org/archives/xml/list
    archives
 to see if the problem was reported already. In this case
    there is probably a fix available, similarly check the 
http://bugzilla.gnome.org/buglist.cgi?product=libxml2registered
    open bugs
.  
Make sure you can reproduce the bug with xmllint or one of the test
    programs found in source in the distribution.
  
Please send the command showing the error as well as the input (as an
    attachment)
Then send the bug with associated information to reproduce it to the mailto:xml@gnome.orgxml@gnome.org  list; if it's really libxml
related I will approve it. Please do not send mail to me directly, it makes
things really hard to track and in some cases I am not the best person to
answer a given question, ask on the list.
To be really clear about support:
  
Support or help requests MUST be sent to
    the list or on bugzilla
 in case of problems, so that the Question
    and Answers can be shared publicly. Failing to do so carries the implicit
    message "I want free support but I don't want to share the benefits with
    others" and is not welcome. I will automatically Carbon-Copy the
    xml@gnome.org mailing list for any technical reply made about libxml2 or
    libxslt.
  
There is no garantee of support, if
    your question remains unanswered after a week, repost it, making sure you
    gave all the detail needed and the information requested.
  
Failing to provide information as requested or double checking first
    for prior feedback also carries the implicit message "the time of the
    library maintainers is less valuable than my time" and might not be
    welcome.
Of course, bugs reported with a suggested patch for fixing them will
probably be processed faster than those without.
If you're looking for help, a quick look at http://mail.gnome.org/archives/xml/the list archive  may actually
provide the answer. I usually send source samples when answering libxml2
usage questions. The 
http://xmlsoft.org/html/book1.htmlauto-generated documentation  is
not as polished as I would like (i need to learn more about DocBook), but
it's a good starting point.
How to help 
You can help the project in various ways, the best thing to do first is to
subscribe to the mailing-list as explained before, check the 
http://mail.gnome.org/archives/xml/archives and the http://bugzilla.gnome.org/buglist.cgi?product=libxml2Gnome bug
database
:
  
Provide patches when you find problems.  
Provide the diffs when you port libxml2 to a new platform. They may not
    be integrated in all cases but help pinpointing portability problems
  and
  
Provide documentation fixes (either as patches to the code comments or
    as HTML diffs).
  
Provide new documentations pieces (translations, examples, etc
  ...).
  
Check the TODO file and try to close one of the items.  
Take one of the points raised in the archive or the bug database and
    provide a fix. 
mailto:daniel@veillard.comGet in touch with me
    
before to avoid synchronization problems and check that the suggested
    fix will fit in nicely :-)
Downloads 
The latest versions of libxml2 can be found on the ftp://xmlsoft.org/xmlsoft.org  server ( http://xmlsoft.org/sources/HTTP , ftp://xmlsoft.org/FTP  and rsync are available), there is also
mirrors (
ftp://ftp.planetmirror.com/pub/xmlsoft/Australia ( http://xmlsoft.planetmirror.com/Web ), ftp://fr.rpmfind.net/pub/libxml/France ) or on the ftp://ftp.gnome.org/pub/GNOME/MIRRORS.htmlGnome FTP server  as ftp://ftp.gnome.org/pub/GNOME/sources/libxml2/2.6/source archive , Antonin Sprinzl also provide 
ftp://gd.tuwien.ac.at/pub/libxml/a
mirror in Austria
. (NOTE that you need both the http://rpmfind.net/linux/RPM/libxml2.htmllibxml(2)  and http://rpmfind.net/linux/RPM/libxml2-devel.htmllibxml(2)-devel packages installed to compile applications using libxml.)
You can find all the history of libxml(2) and libxslt releases in the http://xmlsoft.org/sources/old/old  directory. The precompiled
Windows binaries made by Igor Zlatovic are available in the 
http://xmlsoft.org/sources/win32/win32  directory.
Binary ports:
  
Red Hat RPMs for i386 are available directly on ftp://xmlsoft.org/xmlsoft.org , the source RPM will compile on
    any architecture supported by Red Hat.
  
mailto:igor@zlatkovic.comIgor Zlatkovic  is now the
    maintainer of the Windows port, 
http://www.zlatkovic.com/projects/libxml/index.htmlhe provides
    binaries
.  
Blastwave provides http://www.blastwave.org/packages.php/libxml2Solaris
  binaries
.  
mailto:Steve.Ball@explain.com.auSteve Ball  provides http://www.explain.com.au/oss/libxml2xslt.htmlMac Os X
    binaries
.  
The HP-UX porting center provides http://hpux.connect.org.uk/hppd/hpux/Gnome/HP-UX binaries   
Bull provides precompiled http://gnome.bullfreeware.com/new_index.htmlRPMs for AIX  as
    patr of their GNOME packages
If you know other supported binary ports, please http://veillard.com/contact me .
Snapshot: 
  
Code from the W3C cvs base libxml2 module, updated hourly ftp://xmlsoft.org/libxml2-cvs-snapshot.tar.gzlibxml2-cvs-snapshot.tar.gz .  
Docs, content of the web site, the list archive included ftp://xmlsoft.org/libxml-docs.tar.gzlibxml-docs.tar.gz . Contributions: 
I do accept external contributions, especially if compiling on another
platform,  get in touch with the list to upload the package, wrappers for
various languages have been provided, and can be found in the 
python.htmlbindings section 
Libxml2 is also available from CVS:
  
The http://cvs.gnome.org/viewcvs/libxml2/Gnome CVS
    base
. Check the http://developer.gnome.org/tools/cvs.htmlGnome CVS Tools     page; the CVS module is 
libxml2.
  
  
The libxslt module is also present there Releases 
Items not finished and worked on, get in touch with the list if you want
to help those
  
More testing on RelaxNG  
Finishing up http://www.w3.org/TR/xmlschema-1/XML
  Schemas
The ChangeLog.htmlchange log  describes the recents commits
to the 
http://cvs.gnome.org/viewcvs/libxml2/CVS  code base.
There is the list of public releases:
2.6.23: Jan 5 2006
  
portability fixes: Windows (Rob Richards), getaddrinfo on Windows
    (Kolja Nowak, Rob Richards), icc warnings (Kjartan Maraas),
    --with-minimum compilation fixes (William Brack), error case handling fix
    on Solaris (Albert Chin), don't use 'list' as parameter name reported by
    Samuel Diaz Garcia, more old Unices portability fixes (Albert Chin),
    MinGW compilation (Mark Junker), HP-UX compiler warnings (Rick Jones),
  
  
code cleanup: xmlReportError (Adrian Mouat), remove xmlBufferClose
    (Geert Jansen), unreachable code (Oleksandr Kononenko), refactoring
    parsing code (Bjorn Reese)
  
bug fixes: xmlBuildRelativeURI and empty path (William Brack),
    combinatory explosion and performances in regexp code, leak in
    xmlTextReaderReadString(), xmlStringLenDecodeEntities problem (Massimo
    Morara), Identity Constraints bugs and a segfault (Kasimier Buchcik),
    XPath pattern based evaluation bugs (DV & Kasimier),
    xmlSchemaContentModelDump() memory leak (Kasimier), potential leak in
    xmlSchemaCheckCSelectorXPath(), xmlTextWriterVSprintf() misuse of
    vsnprintf (William Brack), XHTML serialization fix (Rob Richards), CRLF
    split problem (William), issues with non-namespaced attributes in
    xmlAddChild() xmlAddNextSibling() and xmlAddPrevSibling() (Rob Richards),
    HTML parsing of script, Python must not output to stdout (Nic Ferrier),
    exclusive C14N namespace visibility (Aleksey Sanin), XSD dataype
    totalDigits bug (Kasimier Buchcik), error handling when writing to an
    xmlBuffer (Rob Richards), runtest schemas error not reported (Hisashi
    Fujinaka), signed/unsigned problem in date/time code (Albert Chin), fix
    XSI driven XSD validation (Kasimier), parsing of xs:decimal (Kasimier),
    fix DTD writer output (Rob Richards), leak in xmlTextReaderReadInnerXml
    (Gary Coady), regexp bug affecting schemas (Kasimier), configuration of
    runtime debugging (Kasimier), xmlNodeBufGetContent bug on entity refs
    (Oleksandr Kononenko), xmlRegExecPushString2 bug (Sreeni Nair),
    compilation and build fixes (Michael Day), removed dependancies on
    xmlSchemaValidError (Kasimier), bug with <xml:foo/>, more XPath
    pattern based evaluation fixes (Kasimier)
  
improvements: XSD Schemas redefinitions/restrictions (Kasimier
    Buchcik), node copy checks and fix for attribute (Rob Richards), counted
    transition bug in regexps, ctxt->standalone = -2 to indicate no
    standalone attribute was found, add xmlSchemaSetParserStructuredErrors()
    (Kasimier Buchcik), add xmlTextReaderSchemaValidateCtxt() to API
    (Kasimier), handle gzipped HTTP resources (Gary Coady), add
    htmlDocDumpMemoryFormat. (Rob Richards), 
  
documentation: typo (Michael Day), libxml man page (Albert Chin), save
    function to XML buffer (Geert Jansen), small doc fix (Aron Stansvik),
  
2.6.22: Sep 12 2005
  
build fixes: compile without schematron (Stphane Bidoul)  
bug fixes: xmlDebugDumpNode on namespace node (Oleg Paraschenko)i,
    CDATA push parser bug, xmlElemDump problem with XHTML1 doc,
    XML_FEATURE_xxx clash with expat headers renamed XML_WITH_xxx, fix some
    output formatting for meta element (Rob Richards), script and style
    XHTML1 serialization (David Madore), Attribute derivation fixups in XSD
    (Kasimier Buchcik), better IDC error reports (Kasimier Buchcik)
  
improvements: add XML_SAVE_NO_EMPTY xmlSaveOption (Rob Richards), add
    XML_SAVE_NO_XHTML xmlSaveOption, XML Schemas improvements preparing for
    derive (Kasimier Buchcik).
  
documentation: generation of gtk-doc like docs, integration with
    devhelp.
2.6.21: Sep 4 2005
  
build fixes: Cygwin portability fixes (Gerrit P. Haase), calling
    convention problems on Windows (Marcus Boerger), cleanups based on Linus'
    sparse tool, update of win32/configure.js (Rob Richards), remove warnings
    on Windows(Marcus Boerger), compilation without SAX1, detection of the
    Python binary, use $GCC inestad of $CC = 'gcc' (Andrew W. Nosenko),
    compilation/link with threads and old gcc, compile problem by C370 on
    Z/OS,
  
bug fixes: http_proxy environments (Peter Breitenlohner), HTML UTF-8
    bug (Jiri Netolicky), XPath NaN compare bug (William Brack),
    htmlParseScript potential bug, Schemas regexp handling of spaces, Base64
    Schemas comparisons NIST passes, automata build error xsd:all,
    xmlGetNodePath for namespaced attributes (Alexander Pohoyda), xmlSchemas
    foreign namespaces handling, XML Schemas facet comparison (Kupriyanov
    Anatolij), xmlSchemaPSimpleTypeErr error report (Kasimier Buchcik), xml:
    namespace ahndling in Schemas (Kasimier), empty model group in Schemas
    (Kasimier), wilcard in Schemas (Kasimier), URI composition (William),
    xs:anyType in Schemas (Kasimier), Python resolver emmitting error
    messages directly, Python xmlAttr.parent (Jakub Piotr Clapa), trying to
    fix the file path/URI conversion, xmlTextReaderGetAttribute fix (Rob
    Richards), xmlSchemaFreeAnnot memleak (Kasimier), HTML UTF-8
    serialization, streaming XPath, Schemas determinism detection problem,
    XInclude bug, Schemas context type (Dean Hill), validation fix (Derek
    Poon), xmlTextReaderGetAttribute[Ns] namespaces (Rob Richards), Schemas
    type fix (Kuba Nowakowski), UTF-8 parser bug, error in encoding handling,
    xmlGetLineNo fixes, bug on entities handling, entity name extraction in
    error handling with XInclude, text nodes in HTML body tags (Gary Coady),
    xml:id and IDness at the treee level fixes, XPath streaming patterns
  bugs.
  
improvements: structured interfaces for schemas and RNG error reports
    (Marcus Boerger), optimization of the char data inner loop parsing
    (thanks to Behdad Esfahbod for the idea), schematron validation though
    not finished yet, xmlSaveOption to omit XML declaration, keyref match
    error reports (Kasimier), formal expression handling code not plugged
    yet, more lax mode for the HTML parser, parser XML_PARSE_COMPACT option
    for text nodes allocation.
  
documentation: xmllint man page had --nonet duplicated2.6.20: Jul 10 2005
  
build fixes: Windows build (Rob Richards), Mingw compilation (Igor
    Zlatkovic), Windows Makefile (Igor), gcc warnings (Kasimier and
    andriy@google.com), use gcc weak references to pthread to avoid the
    pthread dependancy on Linux, compilation problem (Steve Nairn), compiling
    of subset (Morten Welinder), IPv6/ss_family compilation (William Brack),
    compilation when disabling parts of the library, standalone test
    distribution.
  
bug fixes: bug in lang(), memory cleanup on errors (William Brack),
    HTTP query strings (Aron Stansvik), memory leak in DTD (William), integer
    overflow in XPath (William), nanoftp buffer size, pattern "." apth fixup
    (Kasimier), leak in tree reported by Malcolm Rowe, replaceNode patch
    (Brent Hendricks), CDATA with NULL content (Mark Vakoc), xml:base fixup
    on XInclude (William), pattern fixes (William), attribute bug in
    exclusive c14n (Aleksey Sanin), xml:space and xml:lang with SAX2 (Rob
    Richards), namespace trouble in complex parsing (Malcolm Rowe), XSD type
    QNames fixes (Kasimier), XPath streaming fixups (William), RelaxNG bug
    (Rob Richards), Schemas for Schemas fixes (Kasimier), removal of ID (Rob
    Richards), a small RelaxNG leak, HTML parsing in push mode bug (James
    Bursa), failure to detect UTF-8 parsing bugs in CDATA sections,
    areBlanks() heuristic failure, duplicate attributes in DTD bug
  (William).
  
improvements: lot of work on Schemas by Kasimier Buchcik both on
    conformance and streaming, Schemas validation messages (Kasimier Buchcik,
    Matthew Burgess), namespace removal at the python level (Brent
    Hendricks), Update to new Schemas regression tests from W3C/Nist
    (Kasimier), xmlSchemaValidateFile() (Kasimier), implementation of
    xmlTextReaderReadInnerXml and xmlTextReaderReadOuterXml (James Wert),
    standalone test framework and programs, new DOM import APIs
    xmlDOMWrapReconcileNamespaces() xmlDOMWrapAdoptNode() and
    xmlDOMWrapRemoveNode(), extension of xmllint capabilities for SAX and
    Schemas regression tests, xmlStopParser() available in pull mode too,
    ienhancement to xmllint --shell namespaces support, Windows port of the
    standalone testing tools (Kasimier and William),
    xmlSchemaValidateStream() xmlSchemaSAXPlug() and xmlSchemaSAXUnplug() SAX
    Schemas APIs, Schemas xmlReader support.
2.6.19: Apr 02 2005
  
build fixes: drop .la from RPMs, --with-minimum build fix (William
    Brack), use XML_SOCKLEN_T instead of SOCKLEN_T because it breaks with AIX
    5.3 compiler, fixed elfgcchack.h generation and PLT reduction code on
    Linux/ELF/gcc4
  
bug fixes: schemas type decimal fixups (William Brack), xmmlint return
    code (Gerry Murphy), small schemas fixes (Matthew Burgess and GUY
    Fabrice), workaround "DAV:" namespace brokeness in c14n (Aleksey Sanin),
    segfault in Schemas (Kasimier Buchcik), Schemas attribute validation
    (Kasimier), Prop related functions and xmlNewNodeEatName (Rob Richards),
    HTML serialization of name attribute on a elements, Python error handlers
    leaks and improvement (Brent Hendricks), uninitialized variable in
    encoding code, Relax-NG validation bug, potential crash if
    gnorableWhitespace is NULL, xmlSAXParseDoc and xmlParseDoc signatures,
    switched back to assuming UTF-8 in case no encoding is given at
    serialization time
  
improvements: lot of work on Schemas by Kasimier Buchcik on facets
    checking and also mixed handling.
  
2.6.18: Mar 13 2005
  
build fixes: warnings (Peter Breitenlohner), testapi.c generation,
    Bakefile support (Francesco Montorsi), Windows compilation (Joel Reed),
    some gcc4 fixes, HP-UX portability fixes (Rick Jones).
  
bug fixes: xmlSchemaElementDump namespace (Kasimier Buchcik), push and
    xmlreader stopping on non-fatal errors, thread support for dictionnaries
    reference counting (Gary Coady), internal subset and push problem, URL
    saved in xmlCopyDoc, various schemas bug fixes (Kasimier), Python paths
    fixup (Stephane Bidoul), xmlGetNodePath and namespaces, xmlSetNsProp fix
    (Mike Hommey), warning should not count as error (William Brack),
    xmlCreatePushParser empty chunk, XInclude parser flags (William), cleanup
    FTP and HTTP code to reuse the uri parsing and IPv6 (William),
    xmlTextWriterStartAttributeNS fix (Rob Richards), XMLLINT_INDENT being
    empty (William), xmlWriter bugs (Rob Richards), multithreading on Windows
    (Rich Salz), xmlSearchNsByHref fix (Kasimier), Python binding leak (Brent
    Hendricks), aliasing bug exposed by gcc4 on s390, xmlTextReaderNext bug
    (Rob Richards), Schemas decimal type fixes (William Brack),
    xmlByteConsumed static buffer (Ben Maurer).
  
improvement: speedup parsing comments and DTDs, dictionnary support for
    hash tables, Schemas Identity constraints (Kasimier), streaming XPath
    subset, xmlTextReaderReadString added (Bjorn Reese), Schemas canonical
    values handling (Kasimier), add xmlTextReaderByteConsumed (Aron
  Stansvik),
  
Documentation: Wiki support (Joel Reed)2.6.17: Jan 16 2005
  
build fixes: Windows, warnings removal (William Brack),
    maintainer-clean dependency(William), build in a different directory
    (William), fixing --with-minimum configure build (William), BeOS build
    (Marcin Konicki), Python-2.4 detection (William), compilation on AIX (Dan
    McNichol)
  
bug fixes: xmlTextReaderHasAttributes (Rob Richards), xmlCtxtReadFile()
    to use the catalog(s), loop on output (William Brack), XPath memory leak,
    ID deallocation problem (Steve Shepard), debugDumpNode crash (William),
    warning not using error callback (William), xmlStopParser bug (William),
    UTF-16 with BOM on DTDs (William), namespace bug on empty elements in
    push mode (Rob Richards), line and col computations fixups (Aleksey
    Sanin), xmlURIEscape fix (William), xmlXPathErr on bad range (William),
    patterns with too many steps, bug in RNG choice optimization, line number
    sometimes missing.
  
improvements: XSD Schemas (Kasimier Buchcik), python generator
    (William), xmlUTF8Strpos speedup (William), unicode Python strings
    (William), XSD error reports (Kasimier Buchcik), Python __str__ call
    serialize().
  
new APIs: added xmlDictExists(), GetLineNumber and GetColumnNumber for
    the xmlReader (Aleksey Sanin), Dynamic Shared Libraries APIs (mostly Joel
    Reed), error extraction API from regexps, new XMLSave option for format
    (Phil Shafer)
  
documentation: site improvement (John Fleck), FAQ entries
  (William).
2.6.16: Nov 10 2004
  
general hardening and bug fixing crossing all the API based on new
    automated regression testing
  
build fix: IPv6 build and test on AIX (Dodji Seketeli)  
bug fixes: problem with XML::Libxml reported by Petr Pajas,  encoding
    conversion functions return values, UTF-8 bug affecting XPath reported by
    Markus Bertheau, catalog problem with NULL entries (William Brack)
  
documentation: fix to xmllint man page, some API function descritpion
    were updated.
  
improvements: DTD validation APIs provided at the Python level (Brent
    Hendricks)
2.6.15: Oct 27 2004
  
security fixes on the nanoftp and nanohttp modules  
build fixes: xmllint detection bug in configure, building outside the
    source tree (Thomas Fitzsimmons)
  
bug fixes: HTML parser on broken ASCII chars in names (William), Python
    paths (Malcolm Tredinnick), xmlHasNsProp and default namespace (William),
    saving to python file objects (Malcolm Tredinnick), DTD lookup fix
    (Malcolm), save back <group> in catalogs (William), tree build
    fixes (DV and Rob Richards), Schemas memory bug, structured error handler
    on Python 64bits, thread local memory deallocation, memory leak reported
    by Volker Roth, xmlValidateDtd in the presence of an internal subset,
    entities and _private problem (William), xmlBuildRelativeURI error
    (William).
  
improvements: better XInclude error reports (William), tree debugging
    module and tests, convenience functions at the Reader API (Graham
    Bennett), add support for PI in the HTML parser.
2.6.14: Sep 29 2004
  
build fixes: configure paths for xmllint and xsltproc, compilation
    without HTML parser, compilation warning cleanups (William Brack &
    Malcolm Tredinnick), VMS makefile update (Craig Berry),
  
bug fixes: xmlGetUTF8Char (William Brack), QName properties (Kasimier
    Buchcik), XInclude testing, Notation serialization, UTF8ToISO8859x
    transcoding (Mark Itzcovitz), lots of XML Schemas cleanup and fixes
    (Kasimier), ChangeLog cleanup (Stepan Kasal), memory fixes (Mark Vakoc),
    handling of failed realloc(), out of bound array adressing in Schemas
    date handling, Python space/tabs cleanups (Malcolm Tredinnick), NMTOKENS
    E20 validation fix (Malcolm),
  
improvements: added W3C XML Schemas testsuite (Kasimier Buchcik), add
    xmlSchemaValidateOneElement (Kasimier), Python exception hierearchy
    (Malcolm Tredinnick), Python libxml2 driver improvement (Malcolm
    Tredinnick), Schemas support for xsi:schemaLocation,
    xsi:noNamespaceSchemaLocation, xsi:type (Kasimier Buchcik)
2.6.13: Aug 31 2004
  
build fixes: Windows and zlib (Igor Zlatkovic), -O flag with gcc,
    Solaris compiler warning, fixing RPM BuildRequires,
  
fixes: DTD loading on Windows (Igor), Schemas error reports APIs
    (Kasimier Buchcik), Schemas validation crash, xmlCheckUTF8 (William Brack
    and Julius Mittenzwei), Schemas facet check (Kasimier), default namespace
    problem (William), Schemas hexbinary empty values, encoding error could
    genrate a serialization loop.
  
Improvements: Schemas validity improvements (Kasimier), added --path
    and --load-trace options to xmllint
  
documentation: tutorial update (John Fleck)2.6.12: Aug 22 2004
  
build fixes: fix --with-minimum, elfgcchack.h fixes (Peter
    Breitenlohner), perl path lookup (William), diff on Solaris (Albert
    Chin), some 64bits cleanups.
  
Python: avoid a warning with 2.3 (William Brack), tab and space mixes
    (William), wrapper generator fixes (William), Cygwin support (Gerrit P.
    Haase), node wrapper fix (Marc-Antoine Parent), XML Schemas support
    (Torkel Lyng)
  
Schemas: a lot of bug fixes and improvements from Kasimier Buchcik  
fixes: RVT fixes (William), XPath context resets bug (William), memory
    debug (Steve Hay), catalog white space handling (Peter Breitenlohner),
    xmlReader state after attribute reading (William), structured error
    handler (William), XInclude generated xml:base fixup (William), Windows
    memory reallocation problem (Steve Hay), Out of Memory conditions
    handling (William and Olivier Andrieu), htmlNewDoc() charset bug,
    htmlReadMemory init (William), a posteriori validation DTD base
    (William), notations serialization missing, xmlGetNodePath (Dodji),
    xmlCheckUTF8 (Diego Tartara), missing line numbers on entity
  (William)
  
improvements: DocBook catalog build scrip (William), xmlcatalog tool
    (Albert Chin), xmllint --c14n option, no_proxy environment (Mike Hommey),
    xmlParseInNodeContext() addition, extend xmllint --shell, allow XInclude
    to not generate start/end nodes, extend xmllint --version to include CVS
    tag (William)
  
documentation: web pages fixes, validity API docs fixes (William)
    schemas API fix (Eric Haszlakiewicz), xmllint man page (John Fleck)
2.6.11: July 5 2004
  
Schemas: a lot of changes and improvements by Kasimier Buchcik for
    attributes, namespaces and simple types.
  
build fixes: --with-minimum (William Brack),  some gcc cleanup
    (William), --with-thread-alloc (William)
  
portability: Windows binary package change (Igor Zlatkovic), Catalog
    path on Windows
  
documentation: update to the tutorial (John Fleck), xmllint return code
    (John Fleck), man pages (Ville Skytta),
  
bug fixes: C14N bug serializing namespaces (Aleksey Sanin), testSAX
    properly initialize the library (William), empty node set in XPath
    (William), xmlSchemas errors (William), invalid charref problem pointed
    by Morus Walter, XInclude xml:base generation (William), Relax-NG bug
    with div processing (William), XPointer and xml:base problem(William),
    Reader and entities, xmllint return code for schemas (William), reader
    streaming problem (Steve Ball), DTD serialization problem (William),
    libxml.m4 fixes (Mike Hommey), do not provide destructors as methods on
    Python classes, xmlReader buffer bug, Python bindings memory interfaces
    improvement (with Stphane Bidoul), Fixed the push parser to be back to
    synchronous behaviour.
  
improvement: custom per-thread I/O enhancement (Rob Richards), register
    namespace in debug shell (Stefano Debenedetti), Python based regression
    test for non-Unix users (William), dynamically increase the number of
    XPath extension functions in Python and fix a memory leak (Marc-Antoine
    Parent and William)
  
performance: hack done with Arjan van de Ven to reduce ELF footprint
    and generated code on Linux, plus use gcc runtime profiling to optimize
    the code generated in the RPM packages.
2.6.10: May 17 2004
  
Web page generated for ChangeLog  
build fixes: --without-html problems, make check without make all  
portability: problem with xpath.c on Windows (MSC and Borland), memcmp
    vs. strncmp on Solaris, XPath tests on Windows (Mark Vakoc), C++ do not
    use "list" as parameter name, make tests work with Python 1.5 (Ed
  Davis),
  
improvements: made xmlTextReaderMode public, small buffers resizing
    (Morten Welinder), add --maxmem option to xmllint, add
    xmlPopInputCallback() for Matt Sergeant, refactoring of serialization
    escaping, added escaping customization
  
bugfixes: xsd:extension (Taihei Goi), assorted regexp bugs (William
    Brack), xmlReader end of stream problem, node deregistration with reader,
    URI escaping and filemanes,  XHTML1 formatting (Nick Wellnhofer), regexp
    transition reduction (William), various XSD Schemas fixes (Kasimier
    Buchcik), XInclude fallback problem (William), weird problems with DTD
    (William), structured error handler callback context (William), reverse
    xmlEncodeSpecialChars() behaviour back to escaping '"'
2.6.9: Apr 18 2004
  
implement xml:id Working Draft, relaxed XPath id() checking  
bugfixes: xmlCtxtReset (Brent Hendricks), line number and CDATA (Dave
    Beckett), Relax-NG compilation (William Brack), Regexp patches (with
    William), xmlUriEscape (Mark Vakoc), a Relax-NG notAllowed problem (with
    William), Relax-NG name classes compares (William), XInclude duplicate
    fallback (William), external DTD encoding detection (William), a DTD
    validation bug (William), xmlReader Close() fix, recusive extention
    schemas
  
improvements: use xmlRead* APIs in test tools (Mark Vakoc), indenting
    save optimization, better handle IIS broken HTTP redirect  behaviour (Ian
    Hummel), HTML parser frameset (James Bursa), libxml2-python RPM
    dependancy, XML Schemas union support (Kasimier Buchcik), warning removal
    clanup (William), keep ChangeLog compressed when installing from RPMs
  
documentation: examples and xmlDocDumpMemory docs (John Fleck), new
    example (load, xpath, modify, save), xmlCatalogDump() comments,
  
Windows: Borland C++ builder (Eric Zurcher), work around Microsoft
    compiler NaN handling bug (Mark Vakoc)
2.6.8: Mar 23 2004
  
First step of the cleanup of the serialization code and APIs  
XML Schemas: mixed content (Adam Dickmeiss), QName handling fixes (Adam
    Dickmeiss), anyURI for "" (John Belmonte)
  
Python: Canonicalization C14N support added (Anthony Carrico)  
xmlDocCopyNode() extension (William)  
Relax-NG: fix when processing XInclude results (William), external
    reference in interleave (William), missing error on <choice>
    failure (William), memory leak in schemas datatype facets.
  
xmlWriter: patch for better DTD support (Alfred Mickautsch)  
bug fixes: xmlXPathLangFunction memory leak (Mike Hommey and William
    Brack), no ID errors if using HTML_PARSE_NOERROR, xmlcatalog fallbacks to
    URI on SYSTEM lookup failure, XInclude parse flags inheritance (William),
    XInclude and XPointer fixes for entities (William), XML parser bug
    reported by Holger Rauch, nanohttp fd leak (William),  regexps char
    groups '-' handling (William), dictionnary reference counting problems,
    do not close stderr.
  
performance patches from Petr Pajas  
Documentation fixes: XML_CATALOG_FILES in man pages (Mike Hommey)  
compilation and portability fixes: --without-valid, catalog cleanups
    (Peter Breitenlohner), MingW patch (Roland Schwingel), cross-compilation
    to Windows (Christophe de Vienne),  --with-html-dir fixup (Julio Merino
    Vidal), Windows build (Eric Zurcher)
2.6.7: Feb 23 2004
  
documentation: tutorial updates (John Fleck), benchmark results  
xmlWriter: updates and fixes (Alfred Mickautsch, Lucas Brasilino)  
XPath optimization (Petr Pajas)  
DTD ID handling optimization  
bugfixes: xpath number with  > 19 fractional (William Brack), push
    mode with unescaped '>' characters, fix xmllint --stream --timing, fix
    xmllint --memory --stream memory usage, xmlAttrSerializeTxtContent
    handling NULL, trying to fix Relax-NG/Perl interface.
  
python: 2.3 compatibility, whitespace fixes (Malcolm Tredinnick)  
Added relaxng option to xmllint --shell2.6.6: Feb 12 2004
  
nanohttp and nanoftp: buffer overflow error on URI parsing (Igor and
    William) reported by Yuuichi Teranishi
  
bugfixes: make test and path issues, xmlWriter attribute serialization
    (William Brack), xmlWriter indentation (William), schemas validation
    (Eric Haszlakiewicz), XInclude dictionnaries issues (William and Oleg
    Paraschenko), XInclude empty fallback (William), HTML warnings (William),
    XPointer in XInclude (William), Python namespace serialization,
    isolat1ToUTF8 bound error (Alfred Mickautsch), output of parameter
    entities in internal subset (William), internal subset bug in push mode,
    <xs:all> fix (Alexey Sarytchev)
  
Build: fix for automake-1.8 (Alexander Winston), warnings removal
    (Philip Ludlam), SOCKLEN_T detection fixes (Daniel Richard), fix
    --with-minimum configuration.
  
XInclude: allow the 2001 namespace without warning.  
Documentation: missing example/index.html (John Fleck), version
    dependancies (John Fleck)
  
reader API: structured error reporting (Steve Ball)  
Windows compilation: mingw, msys (Mikhail Grushinskiy), function
    prototype (Cameron Johnson), MSVC6 compiler warnings, _WINSOCKAPI_
  patch
  
Parsers: added xmlByteConsumed(ctxt) API to get the byte offest in
    input.
2.6.5: Jan 25 2004
  
Bugfixes: dictionnaries for schemas (William Brack), regexp segfault
    (William), xs:all problem (William), a number of XPointer bugfixes
    (William), xmllint error go to stderr, DTD validation problem with
    namespace, memory leak (William), SAX1 cleanup and minimal options fixes
    (Mark Vadoc), parser context reset on error (Shaun McCance), XPath union
    evaluation problem (William) , xmlReallocLoc with NULL (Aleksey Sanin),
    XML Schemas double free (Steve Ball), XInclude with no href, argument
    callbacks order for XPath callbacks (Frederic Peters)
  
Documentation: python scripts (William Brack), xslt stylesheets (John
    Fleck), doc (Sven Zimmerman), I/O example.
  
Python bindings: fixes (William), enum support (Stphane Bidoul),
    structured error reporting (Stphane Bidoul)
  
XInclude: various fixes for conformance, problem related to dictionnary
    references (William & me), recursion (William)
  
xmlWriter: indentation (Lucas Brasilino), memory leaks (Alfred
    Mickautsch),
  
xmlSchemas: normalizedString datatype (John Belmonte)  
code cleanup for strings functions (William)  
Windows: compiler patches (Mark Vakoc)  
Parser optimizations, a few new XPath and dictionnary APIs for future
    XSLT optimizations.
2.6.4: Dec 24 2003
  
Windows build fixes (Igor Zlatkovic)  
Some serious XInclude problems reported by Oleg Paraschenko and  
Unix and Makefile packaging fixes (me, William Brack,  
Documentation improvements (John Fleck, William Brack), example fix
    (Lucas Brasilino)
  
bugfixes: xmlTextReaderExpand() with xmlReaderWalker, XPath handling of
    NULL strings (William Brack) , API building reader or parser from
    filedescriptor should not close it, changed XPath sorting to be stable
    again (William Brack), xmlGetNodePath() generating '(null)' (William
    Brack), DTD validation and namespace bug (William Brack), XML Schemas
    double inclusion behaviour
2.6.3: Dec 10 2003
  
documentation updates and cleanup (DV, William Brack, John Fleck)  
added a repository of examples, examples from Aleksey Sanin, Dodji
    Seketeli, Alfred Mickautsch
  
Windows updates: Mark Vakoc, Igor Zlatkovic, Eric Zurcher, Mingw
    (Kenneth Haley)
  
Unicode range checking (William Brack)  
code cleanup (William Brack)  
Python bindings: doc (John Fleck),  bug fixes  
UTF-16 cleanup and BOM issues (William Brack)  
bug fixes: ID and xmlReader validation, XPath (William Brack),
    xmlWriter (Alfred Mickautsch), hash.h inclusion problem, HTML parser
    (James Bursa), attribute defaulting and validation, some serialization
    cleanups, XML_GET_LINE macro, memory debug when using threads (William
    Brack), serialization of attributes and entities content, xmlWriter
    (Daniel Schulman)
  
XInclude bugfix, new APIs and update to the last version including the
    namespace change.
  
XML Schemas improvements: include (Robert Stepanek), import and
    namespace handling, fixed the regression tests troubles, added examples
    based on Eric van der Vlist book, regexp fixes
  
preliminary pattern support for streaming (needed for schemas
    constraints), added xmlTextReaderPreservePattern() to collect subdocument
    when streaming.
  
various fixes in the structured error handling2.6.2: Nov 4 2003
  
XPath context unregistration fixes  
text node coalescing fixes (Mark Lilback)  
API to screate a W3C Schemas from an existing document (Steve Ball)  
BeOS patches (Marcin 'Shard' Konicki)  
xmlStrVPrintf function added (Aleksey Sanin)  
compilation fixes (Mark Vakoc)  
stdin parsing fix (William Brack)  
a posteriori DTD validation fixes  
xmlReader bug fixes: Walker fixes, python bindings  
fixed xmlStopParser() to really stop the parser and errors  
always generate line numbers when using the new xmlReadxxx
  functions
  
added XInclude support to the xmlReader interface  
implemented XML_PARSE_NONET parser option  
DocBook XSLT processing bug fixed  
HTML serialization for <p> elements (William Brack and me)  
XPointer failure in XInclude are now handled as resource errors  
fixed xmllint --html to use the HTML serializer on output (added
    --xmlout to implement the previous behaviour of saving it using the XML
    serializer)
2.6.1: Oct 28 2003
  
Mostly bugfixes after the big 2.6.0 changes  
Unix compilation patches: libxml.m4 (Patrick Welche), warnings cleanup
    (William Brack)
  
Windows compilation patches (Joachim Bauch, Stephane Bidoul, Igor
    Zlatkovic)
  
xmlWriter bugfix (Alfred Mickautsch)  
chvalid.[ch]: couple of fixes from Stephane Bidoul  
context reset: error state reset, push parser reset (Graham
  Bennett)
  
context reuse: generate errors if file is not readable  
defaulted attributes for element coming from internal entities
    (Stephane Bidoul)
  
Python: tab and spaces mix (William Brack)  
Error handler could crash in DTD validation in 2.6.0  
xmlReader: do not use the document or element _private field  
testSAX.c: avoid a problem with some PIs (Massimo Morara)  
general bug fixes: mandatory encoding in text decl, serializing
    Document Fragment nodes, xmlSearchNs 2.6.0 problem (Kasimier Buchcik),
    XPath errors not reported,  slow HTML parsing of large documents.
2.6.0: Oct 20 2003
  
Major revision release: should be API and ABI compatible but got a lot
    of change
  
Increased the library modularity, far more options can be stripped out,
    a --with-minimum configuration will weight around 160KBytes
  
Use per parser and per document dictionnary, allocate names and small
    text nodes from the dictionnary
  
Switch to a SAX2 like parser rewrote most of the XML parser core,
    provides namespace resolution and defaulted attributes, minimize memory
    allocations and copies, namespace checking and specific error handling,
    immutable buffers, make predefined entities static structures, etc...
  
rewrote all the error handling in the library, all errors can be
    intercepted at a structured level, with precise information
  available.
  
New simpler and more generic XML and HTML parser APIs, allowing to
    easilly modify the parsing options and reuse parser context for multiple
    consecutive documents.
  
Similar new APIs for the xmlReader, for options and reuse, provided new
    functions to access content as const strings, use them for Python
  bindings
  
a  lot of other smaller API improvements: xmlStrPrintf (Aleksey Sanin),
    Walker i.e. reader on a document tree based on Alfred Mickautsch code,
    make room in nodes for line numbers, reference counting and future PSVI
    extensions, generation of character ranges to be checked with faster
    algorithm (William),  xmlParserMaxDepth (Crutcher Dunnavant), buffer
    access
  
New xmlWriter API provided by Alfred Mickautsch  
Schemas: base64 support by Anthony Carrico  
Parser<->HTTP integration fix, proper processing of the Mime-Type
    and charset informations if available.
  
Relax-NG: bug fixes including the one reported by Martijn Faassen and
    zeroOrMore, better error reporting.
  
Python bindings (Stphane Bidoul), never use stdout for errors
  output
  
Portability: all the headers have macros for export and calling
    convention definitions (Igor Zlatkovic), VMS update (Craig A. Berry),
    Windows: threads (Jesse Pelton), Borland compiler (Eric Zurcher,  Igor),
    Mingw (Igor), typos (Mark Vakoc),  beta version (Stephane Bidoul),
    warning cleanups on AIX and MIPS compilers (William Brack), BeOS (Marcin
    'Shard' Konicki)
  
Documentation fixes and README (William Brack), search fix (William),
    tutorial updates (John Fleck), namespace docs (Stefan Kost)
  
Bug fixes: xmlCleanupParser (Dave Beckett), threading uninitialized
    mutexes, HTML doctype lowercase,  SAX/IO (William), compression detection
    and restore (William), attribute declaration in DTDs (William), namespace
    on attribute in HTML output (William), input filename (Rob Richards),
    namespace DTD validation, xmlReplaceNode (Chris Ryland), I/O callbacks
    (Markus Keim), CDATA serialization (Shaun McCance), xmlReader (Peter
    Derr), high codepoint charref like &#x10FFFF;, buffer access in push
    mode (Justin Fletcher), TLS threads on Windows (Jesse Pelton), XPath bug
    (William), xmlCleanupParser (Marc Liyanage), CDATA output (William), HTTP
    error handling.
  
xmllint options: --dtdvalidfpi for Tobias Reif, --sax1 for compat
    testing,  --nodict for building without tree dictionnary, --nocdata to
    replace CDATA by text, --nsclean to remove surperfluous  namespace
    declarations
  
added xml2-config --libtool-libs option from Kevin P. Fleming  
a lot of profiling and tuning of the code, speedup patch for
    xmlSearchNs() by Luca Padovani. The xmlReader should do far less
    allocation and it speed should get closer to SAX. Chris Anderson worked
    on speeding and cleaning up repetitive checking code.
  
cleanup of "make tests"  
libxml-2.0-uninstalled.pc from Malcolm Tredinnick  
deactivated the broken docBook SGML parser code and plugged the XML
    parser instead.
2.5.11: Sep 9 2003
A bugfix only release:
  
risk of crash in Relax-NG  
risk of crash when using multithreaded programs2.5.10: Aug 15 2003
A bugfixes only release
  
Windows Makefiles (William Brack)  
UTF-16 support fixes (Mark Itzcovitz)  
Makefile and portability (William Brack) automake, Linux alpha, Mingw
    on Windows (Mikhail Grushinskiy)
  
HTML parser (Oliver Stoeneberg)  
XInclude performance problem reported by Kevin Ruscoe  
XML parser performance problem reported by Grant Goodale  
xmlSAXParseDTD() bug fix from Malcolm Tredinnick  
and a couple other cleanup2.5.9: Aug 9 2003
  
bugfixes: IPv6 portability, xmlHasNsProp (Markus Keim), Windows build
    (Wiliam Brake, Jesse Pelton, Igor), Schemas (Peter Sobisch), threading
    (Rob Richards), hexBinary type (), UTF-16 BOM (Dodji Seketeli),
    xmlReader, Relax-NG schemas compilation, namespace handling,  EXSLT (Sean
    Griffin), HTML parsing problem (William Brack), DTD validation for mixed
    content + namespaces, HTML serialization, library initialization,
    progressive HTML parser
  
better interfaces for Relax-NG error handling (Joachim Bauch, )  
adding xmlXIncludeProcessTree() for XInclud'ing in a subtree  
doc fixes and improvements (John Fleck)  
configure flag for -with-fexceptions when embedding in C++  
couple of new UTF-8 helper functions (William Brack)  
general encoding cleanup + ISO-8859-x without iconv (Peter Jacobi)  
xmlTextReader cleanup + enum for node types (Bjorn Reese)  
general compilation/warning cleanup Solaris/HP-UX/... (William
  Brack)
2.5.8: Jul 6 2003
  
bugfixes: XPath, XInclude, file/URI mapping, UTF-16 save (Mark
    Itzcovitz), UTF-8 checking, URI saving, error printing (William Brack),
    PI related memleak, compilation without schemas or without xpath (Joerg
    Schmitz-Linneweber/Garry Pennington), xmlUnlinkNode problem with DTDs,
    rpm problem on , i86_64, removed a few compilation problems from 2.5.7,
    xmlIOParseDTD, and xmlSAXParseDTD (Malcolm Tredinnick)
  
portability: DJGPP (MsDos) , OpenVMS (Craig A. Berry)  
William Brack fixed multithreading lock problems  
IPv6 patch for FTP and HTTP accesses (Archana Shah/Wipro)  
Windows fixes (Igor Zlatkovic,  Eric Zurcher), threading (Stphane
    Bidoul)
  
A few W3C Schemas Structure improvements  
W3C Schemas Datatype improvements (Charlie Bozeman)  
Python bindings for thread globals (Stphane Bidoul), and method/class
    generator
  
added --nonet option to xmllint  
documentation improvements (John Fleck)2.5.7: Apr 25 2003
  
Relax-NG: Compiling to regexp and streaming validation on top of the
    xmlReader interface, added to xmllint --stream
  
xmlReader: Expand(), Next() and DOM access glue, bug fixes  
Support for large files: RGN validated a 4.5GB instance  
Thread support is now configured in by default  
Fixes: update of the Trio code (Bjorn), WXS Date and Duration fixes
    (Charles Bozeman), DTD and namespaces (Brent Hendricks), HTML push parser
    and zero bytes handling, some missing Windows file path conversions,
    behaviour of the parser and validator in the presence of "out of memory"
    error conditions
  
extended the API to be able to plug a garbage collecting memory
    allocator, added xmlMallocAtomic() and modified the allocations
    accordingly.
  
Performances: removed excessive malloc() calls, speedup of the push and
    xmlReader interfaces, removed excessive thread locking
  
Documentation: man page (John Fleck), xmlReader documentation  
Python: adding binding for xmlCatalogAddLocal (Brent M Hendricks)2.5.6: Apr 1 2003
  
Fixed W3C XML Schemas datatype, should be compliant now except for
    binHex and base64 which are not supported yet.
  
bug fixes: non-ASCII IDs, HTML output, XInclude on large docs and
    XInclude entities handling, encoding detection on external subsets, XML
    Schemas bugs and memory leaks, HTML parser (James Bursa)
  
portability: python/trio (Albert Chin), Sun compiler warnings  
documentation: added --relaxng option to xmllint man page (John)  
improved error reporting: xml:space, start/end tag mismatches, Relax NG
    errors
2.5.5: Mar 24 2003
  
Lot of fixes on the Relax NG implementation. More testing including
    DocBook and TEI examples.
  
Increased the support for W3C XML Schemas datatype  
Several bug fixes in the URI handling layer  
Bug fixes: HTML parser, xmlReader, DTD validation, XPath, encoding
    conversion, line counting in the parser.
  
Added support for $XMLLINT_INDENT environment variable, FTP delete  
Fixed the RPM spec file name2.5.4: Feb 20 2003
  
Conformance testing and lot of fixes on Relax NG and XInclude
    implementation
  
Implementation of XPointer element() scheme  
Bug fixes: XML parser, XInclude entities merge, validity checking on
    namespaces,
    
2 serialization bugs, node info generation problems, a DTD regexp
    generation problem.
  
  
Portability: windows updates and path canonicalization (Igor)  
A few typo fixes (Kjartan Maraas)  
Python bindings generator fixes (Stephane Bidoul)2.5.3: Feb 10 2003
  
RelaxNG and XML Schemas datatypes improvements, and added a first
    version of RelaxNG Python bindings
  
Fixes: XLink (Sean Chittenden), XInclude (Sean Chittenden), API fix for
    serializing namespace nodes, encoding conversion bug, XHTML1
  serialization
  
Portability fixes: Windows (Igor), AMD 64bits RPM spec file2.5.2: Feb 5 2003
  
First implementation of RelaxNG, added --relaxng flag to xmllint  
Schemas support now compiled in by default.  
Bug fixes: DTD validation, namespace checking, XInclude and entities,
    delegateURI in XML Catalogs, HTML parser, XML reader (Stphane Bidoul),
    XPath parser and evaluation,  UTF8ToUTF8 serialization, XML reader memory
    consumption, HTML parser, HTML serialization in the presence of
  namespaces
  
added an HTML API to check elements and attributes.  
Documentation improvement, PDF for the tutorial (John Fleck), doc
    patches (Stefan Kost)
  
Portability fixes: NetBSD (Julio Merino), Windows (Igor Zlatkovic)  
Added python bindings for XPointer, contextual error reporting
    (Stphane Bidoul)
  
URI/file escaping problems (Stefano Zacchiroli)2.5.1: Jan 8 2003
  
Fixes a memory leak and configuration/compilation problems in 2.5.0  
documentation updates (John)  
a couple of XmlTextReader fixes2.5.0: Jan 6 2003
  
New xmlreader.htmlXmltextReader interface  based on C#
    API (with help of Stphane Bidoul)
  
Windows: more exports, including the new API (Igor)  
XInclude fallback fix  
Python: bindings for the new API, packaging (Stphane Bidoul),
    drv_libxml2.py Python xml.sax driver (Stphane Bidoul), fixes, speedup
    and iterators for Python-2.2 (Hannu Krosing)
  
Tutorial fixes (john Fleck and Niraj Tolia) xmllint man update
  (John)
  
Fix an XML parser bug raised by Vyacheslav Pindyura  
Fix for VMS serialization (Nigel Hall) and config (Craig A. Berry)  
Entities handling fixes  
new API to optionally track node creation and deletion (Lukas
  Schroeder)
  
Added documentation for the XmltextReader interface and some guidelines.htmlXML guidelines 2.4.30: Dec 12 2002
  
2.4.29 broke the python bindings, rereleasing  
Improvement/fixes of the XML API generator, and couple of minor code
    fixes.
2.4.29: Dec 11 2002
  
Windows fixes (Igor): Windows CE port, pthread linking, python bindings
    (Stphane Bidoul), Mingw (Magnus Henoch), and export list updates
  
Fix for prev in python bindings (ERDI Gergo)  
Fix for entities handling (Marcus Clarke)  
Refactored the XML and HTML dumps to a single code path, fixed XHTML1
    dump
  
Fix for URI parsing when handling URNs with fragment identifiers  
Fix for HTTP URL escaping problem  
added an TextXmlReader (C#) like API (work in progress)  
Rewrote the API in XML generation script, includes a C parser and saves
    more informations needed for C# bindings
2.4.28: Nov 22 2002
  
a couple of python binding fixes  
2 bug fixes in the XML push parser  
potential memory leak removed (Martin Stoilov)  
fix to the configure script for Unix (Dimitri Papadopoulos)  
added encoding support for XInclude parse="text"  
autodetection of XHTML1 and specific serialization rules added  
nasty threading bug fixed (William Brack)2.4.27: Nov 17 2002
  
fixes for the Python bindings  
a number of bug fixes: SGML catalogs, xmlParseBalancedChunkMemory(),
    HTML parser,  Schemas (Charles Bozeman), document fragment support
    (Christian Glahn), xmlReconciliateNs (Brian Stafford), XPointer,
    xmlFreeNode(), xmlSAXParseMemory (Peter Jones), xmlGetNodePath (Petr
    Pajas), entities processing
  
added grep to xmllint --shell  
VMS update patch from Craig A. Berry  
cleanup of the Windows build with support for more compilers (Igor),
    better thread support on Windows
  
cleanup of Unix Makefiles and spec file  
Improvements to the documentation (John Fleck)2.4.26: Oct 18 2002
  
Patches for Windows CE port, improvements on Windows paths handling  
Fixes to the validation  code (DTD and Schemas), xmlNodeGetPath() ,
    HTML serialization, Namespace compliance,  and a number of small
  problems
2.4.25: Sep 26 2002
  
A number of bug fixes: XPath, validation, Python bindings, DOM and
    tree, xmlI/O,  Html
  
Serious rewrite of XInclude  
Made XML Schemas regexp part of the default build and APIs, small fix
    and improvement of the regexp core
  
Changed the validation code to reuse XML Schemas regexp APIs  
Better handling of Windows file paths, improvement of Makefiles (Igor,
    Daniel Gehriger, Mark Vakoc)
  
Improved the python I/O bindings, the tests, added resolver and regexp
    APIs
  
New logos from Marc Liyanage  
Tutorial improvements: John Fleck, Christopher Harris  
Makefile: Fixes for AMD x86_64 (Mandrake), DESTDIR (Christophe
  Merlet)
  
removal of all stderr/perror use for error reporting  
Better error reporting: XPath and DTD validation  
update of the trio portability layer (Bjorn Reese)2.4.24: Aug 22 2002
  
XPath fixes (William), xf:escape-uri() (Wesley Terpstra)  
Python binding fixes: makefiles (William), generator, rpm build, x86-64
    (fcrozat)
  
HTML <style> and boolean attributes serializer fixes  
C14N improvements by Aleksey  
doc cleanups: Rick Jones  
Windows compiler makefile updates: Igor and Elizabeth Barham  
XInclude: implementation of fallback and xml:base fixup added2.4.23: July 6 2002
  
performances patches: Peter Jacobi  
c14n fixes, testsuite and performances: Aleksey Sanin  
added xmlDocFormatDump: Chema Celorio  
new tutorial: John Fleck  
new hash functions and performances: Sander Vesik, portability fix from
    Peter Jacobi
  
a number of bug fixes: XPath (William Brack, Richard Jinks), XML and
    HTML parsers, ID lookup function
  
removal of all remaining sprintf: Aleksey Sanin2.4.22: May 27 2002
  
a number of bug fixes: configure scripts, base handling, parser, memory
    usage, HTML parser, XPath, documentation (Christian Cornelssen),
    indentation, URI parsing
  
Optimizations for XMLSec, fixing and making public some of the network
    protocol handlers (Aleksey)
  
performance patch from Gary Pennington  
Charles Bozeman provided date and time support for XML Schemas
  datatypes
2.4.21: Apr 29 2002
This release is both a bug fix release and also contains the early XML
Schemas 
http://www.w3.org/TR/xmlschema-1/structures  and http://www.w3.org/TR/xmlschema-2/datatypes  code, beware, all
interfaces are likely to change, there is huge holes, it is clearly a work in
progress and don't even think of putting this code in a production system,
it's actually not compiled in by default. The real fixes are:
  
a couple of bugs or limitations introduced in 2.4.20  
patches for Borland C++ and MSC by Igor  
some fixes on XPath strings and conformance patches by Richard
  Jinks
  
patch from Aleksey for the ExcC14N specification  
OSF/1 bug fix by Bjorn2.4.20: Apr 15 2002
  
bug fixes: file descriptor leak, XPath, HTML output, DTD validation  
XPath conformance testing by Richard Jinks  
Portability fixes: Solaris, MPE/iX, Windows, OSF/1, python bindings,
    libxml.m4
2.4.19: Mar 25 2002
  
bug fixes: half a dozen XPath bugs, Validation, ISO-Latin to UTF8
    encoder
  
portability fixes in the HTTP code  
memory allocation checks using valgrind, and profiling tests  
revamp of the Windows build and Makefiles2.4.18: Mar 18 2002
  
bug fixes: tree, SAX, canonicalization, validation, portability,
  XPath
  
removed the --with-buffer option it was becoming unmaintainable  
serious cleanup of the Python makefiles  
speedup patch to XPath very effective for DocBook stylesheets  
Fixes for Windows build, cleanup of the documentation2.4.17: Mar 8 2002
  
a lot of bug fixes, including "namespace nodes have no parents in
  XPath"
  
fixed/improved the Python wrappers, added more examples and more
    regression tests, XPath extension functions can now return node-sets
  
added the XML Canonicalization support from Aleksey Sanin2.4.16: Feb 20 2002
  
a lot of bug fixes, most of them were triggered by the XML Testsuite
    from OASIS and W3C. Compliance has been significantly improved.
  
a couple of portability fixes too.2.4.15: Feb 11 2002
  
Fixed the Makefiles, especially the python module ones  
A few bug fixes and cleanup  
Includes cleanup2.4.14: Feb 8 2002
  
Change of License to the http://www.opensource.org/licenses/mit-license.htmlMIT
    License
 basically for integration in XFree86 codebase, and removing
    confusion around the previous dual-licensing
  
added Python bindings, beta software but should already be quite
    complete
  
a large number of fixes and cleanups, especially for all tree
    manipulations
  
cleanup of the headers, generation of a reference API definition in
  XML
2.4.13: Jan 14 2002
  
update of the documentation: John Fleck and Charlie Bozeman  
cleanup of timing code from Justin Fletcher  
fixes for Windows and initial thread support on Win32: Igor and Serguei
    Narojnyi
  
Cygwin patch from Robert Collins  
added xmlSetEntityReferenceFunc() for Keith Isdale work on xsldbg2.4.12: Dec 7 2001
  
a few bug fixes: thread (Gary Pennington), xmllint (Geert Kloosterman),
    XML parser (Robin Berjon), XPointer (Danny Jamshy), I/O cleanups
  (robert)
  
Eric Lavigne contributed project files for MacOS  
some makefiles cleanups2.4.11: Nov 26 2001
  
fixed a couple of errors in the includes, fixed a few bugs, some code
    cleanups
  
xmllint man pages improvement by Heiko Rupp  
updated VMS build instructions from John A Fotheringham  
Windows Makefiles updates from Igor2.4.10: Nov 10 2001
  
URI escaping fix (Joel Young)  
added xmlGetNodePath() (for paths or XPointers generation)  
Fixes namespace handling problems when using DTD and validation  
improvements on xmllint: Morus Walter patches for --format and
    --encode, Stefan Kost and Heiko Rupp improvements on the --shell
  
fixes for xmlcatalog linking pointed by Weiqi Gao  
fixes to the HTML parser2.4.9: Nov 6 2001
  
fixes more catalog bugs  
avoid a compilation problem, improve xmlGetLineNo()2.4.8: Nov 4 2001
  
fixed SGML catalogs broken in previous release, updated xmlcatalog
  tool
  
fixed a compile errors and some includes troubles.2.4.7: Oct 30 2001
  
exported some debugging interfaces  
serious rewrite of the catalog code  
integrated Gary Pennington thread safety patch, added configure option
    and regression tests
  
removed an HTML parser bug  
fixed a couple of potentially serious validation bugs  
integrated the SGML DocBook support in xmllint  
changed the nanoftp anonymous login passwd  
some I/O cleanup and a couple of interfaces for Perl wrapper  
general bug fixes  
updated xmllint man page by John Fleck  
some VMS and Windows updates2.4.6: Oct 10 2001
  
added an updated man pages by John Fleck  
portability and configure fixes  
an infinite loop on the HTML parser was removed (William)  
Windows makefile patches from Igor  
fixed half a dozen bugs reported for libxml or libxslt  
updated xmlcatalog to be able to modify SGML super catalogs2.4.5: Sep 14 2001
  
Remove a few annoying bugs in 2.4.4  
forces the HTML serializer to output decimal charrefs since some
    version of Netscape can't handle hexadecimal ones
1.8.16: Sep 14 2001
  
maintenance release of the old libxml1 branch, couple of bug and
    portability fixes
2.4.4: Sep 12 2001
  
added --convert to xmlcatalog, bug fixes and cleanups of XML
  Catalog
  
a few bug fixes and some portability changes  
some documentation cleanups2.4.3:  Aug 23 2001
  
XML Catalog support see the doc  
New NaN/Infinity floating point code  
A few bug fixes2.4.2:  Aug 15 2001
  
adds xmlLineNumbersDefault() to control line number generation  
lot of bug fixes  
the Microsoft MSC projects files should now be up to date  
inheritance of namespaces from DTD defaulted attributes  
fixes a serious potential security bug  
added a --format option to xmllint2.4.1:  July 24 2001
  
possibility to keep line numbers in the tree  
some computation NaN fixes  
extension of the XPath API  
cleanup for alpha and ia64 targets  
patch to allow saving through HTTP PUT or POST2.4.0: July 10 2001
  
Fixed a few bugs in XPath, validation, and tree handling.  
Fixed XML Base implementation, added a couple of examples to the
    regression tests
  
A bit of cleanup2.3.14: July 5 2001
  
fixed some entities problems and reduce memory requirement when
    substituting them
  
lots of improvements in the XPath queries interpreter can be
    substantially faster
  
Makefiles and configure cleanups  
Fixes to XPath variable eval, and compare on empty node set  
HTML tag closing bug fixed  
Fixed an URI reference computation problem when validating2.3.13: June 28 2001
  
2.3.12 configure.in was broken as well as the push mode XML parser  
a few more fixes for compilation on Windows MSC by Yon Derek1.8.14: June 28 2001
  
Zbigniew Chyla gave a patch to use the old XML parser in push mode  
Small Makefile fix2.3.12: June 26 2001
  
lots of cleanup  
a couple of validation fix  
fixed line number counting  
fixed serious problems in the XInclude processing  
added support for UTF8 BOM at beginning of entities  
fixed a strange gcc optimizer bugs in xpath handling of float, gcc-3.0
    miscompile uri.c (William), Thomas Leitner provided a fix for the
    optimizer on Tru64
  
incorporated Yon Derek and Igor Zlatkovic  fixes and improvements for
    compilation on Windows MSC
  
update of libxml-doc.el (Felix Natter)  
fixed 2 bugs in URI normalization code2.3.11: June 17 2001
  
updates to trio, Makefiles and configure should fix some portability
    problems (alpha)
  
fixed some HTML serialization problems (pre, script, and block/inline
    handling), added encoding aware APIs, cleanup of this code
  
added xmlHasNsProp()  
implemented a specific PI for encoding support in the DocBook SGML
    parser
  
some XPath fixes (-Infinity, / as a function parameter and namespaces
    node selection)
  
fixed a performance problem and an error in the validation code  
fixed XInclude routine to implement the recursive behaviour  
fixed xmlFreeNode problem when libxml is included statically twice  
added --version to xmllint for bug reports2.3.10: June 1 2001
  
fixed the SGML catalog support  
a number of reported bugs got fixed, in XPath, iconv detection,
    XInclude processing
  
XPath string function should now handle unicode correctly2.3.9: May 19 2001
Lots of bugfixes, and added a basic SGML catalog support:
  
HTML push bugfix #54891 and another patch from Jonas Borgstrm  
some serious speed optimization again  
some documentation cleanups  
trying to get better linking on Solaris (-R)  
XPath API cleanup from Thomas Broyer  
Validation bug fixed #54631, added a patch from Gary Pennington, fixed
    xmlValidGetValidElements()
  
Added an INSTALL file  
Attribute removal added to API: #54433  
added a basic support for SGML catalogs  
fixed xmlKeepBlanksDefault(0) API  
bugfix in xmlNodeGetLang()  
fixed a small configure portability problem  
fixed an inversion of SYSTEM and PUBLIC identifier in HTML document1.8.13: May 14 2001
  
bugfixes release of the old libxml1 branch used by Gnome2.3.8: May 3 2001
  
Integrated an SGML DocBook parser for the Gnome project  
Fixed a few things in the HTML parser  
Fixed some XPath bugs raised by XSLT use, tried to fix the floating
    point portability issue
  
Speed improvement (8M/s for SAX, 3M/s for DOM, 1.5M/s for
    DOM+validation using the XML REC as input and a 700MHz celeron).
  
incorporated more Windows cleanup  
added xmlSaveFormatFile()  
fixed problems in copying nodes with entities references (gdome)  
removed some troubles surrounding the new validation module2.3.7: April 22 2001
  
lots of small bug fixes, corrected XPointer  
Non deterministic content model validation support  
added xmlDocCopyNode for gdome2  
revamped the way the HTML parser handles end of tags  
XPath: corrections of namespaces support and number formatting  
Windows: Igor Zlatkovic patches for MSC compilation  
HTML output fixes from P C Chow and William M. Brack  
Improved validation speed sensible for DocBook  
fixed a big bug with ID declared in external parsed entities  
portability fixes, update of Trio from Bjorn Reese2.3.6: April 8 2001
  
Code cleanup using extreme gcc compiler warning options, found and
    cleared half a dozen potential problem
  
the Eazel team found an XML parser bug  
cleaned up the user of some of the string formatting function. used the
    trio library code to provide the one needed when the platform is missing
    them
  
xpath: removed a memory leak and fixed the predicate evaluation
    problem, extended the testsuite and cleaned up the result. XPointer seems
    broken ...
2.3.5: Mar 23 2001
  
Biggest change is separate parsing and evaluation of XPath expressions,
    there is some new APIs for this too
  
included a number of bug fixes(XML push parser, 51876, notations,
  52299)
  
Fixed some portability issues2.3.4: Mar 10 2001
  
Fixed bugs #51860 and #51861  
Added a global variable xmlDefaultBufferSize to allow default buffer
    size to be application tunable.
  
Some cleanup in the validation code, still a bug left and this part
    should probably be rewritten to support ambiguous content model :-\
  
Fix a couple of serious bugs introduced or raised by changes in 2.3.3
    parser
  
Fixed another bug in xmlNodeGetContent()  
Bjorn fixed XPath node collection and Number formatting  
Fixed a loop reported in the HTML parsing  
blank space are reported even if the Dtd content model proves that they
    are formatting spaces, this is for XML conformance
2.3.3: Mar 1 2001
  
small change in XPath for XSLT  
documentation cleanups  
fix in validation by Gary Pennington  
serious parsing performances improvements2.3.2: Feb 24 2001
  
chasing XPath bugs, found a bunch, completed some TODO  
fixed a Dtd parsing bug  
fixed a bug in xmlNodeGetContent  
ID/IDREF support partly rewritten by Gary Pennington2.3.1: Feb 15 2001
  
some XPath and HTML bug fixes for XSLT  
small extension of the hash table interfaces for DOM gdome2
    implementation
  
A few bug fixes2.3.0: Feb 8 2001 (2.2.12 was on 25 Jan but I didn't kept track)
  
Lots of XPath bug fixes  
Add a mode with Dtd lookup but without validation error reporting for
    XSLT
  
Add support for text node without escaping (XSLT)  
bug fixes for xmlCheckFilename  
validation code bug fixes from Gary Pennington  
Patch from Paul D. Smith correcting URI path normalization  
Patch to allow simultaneous install of libxml-devel and
  libxml2-devel
  
the example Makefile is now fixed  
added HTML to the RPM packages  
tree copying bugfixes  
updates to Windows makefiles  
optimization patch from Bjorn Reese2.2.11: Jan 4 2001
  
bunch of bug fixes (memory I/O, xpath, ftp/http, ...)  
added htmlHandleOmittedElem()  
Applied Bjorn Reese's IPV6 first patch  
Applied Paul D. Smith patches for validation of XInclude results  
added XPointer xmlns() new scheme support2.2.10: Nov 25 2000
  
Fix the Windows problems of 2.2.8  
integrate OpenVMS patches  
better handling of some nasty HTML input  
Improved the XPointer implementation  
integrate a number of provided patches2.2.9: Nov 25 2000
  
erroneous release :-(2.2.8: Nov 13 2000
  
First version of http://www.w3.org/TR/xincludeXInclude     support
  
Patch in conditional section handling  
updated MS compiler project  
fixed some XPath problems  
added an URI escaping function  
some other bug fixes2.2.7: Oct 31 2000
  
added message redirection  
XPath improvements (thanks TOM !)  
xmlIOParseDTD() added  
various small fixes in the HTML, URI, HTTP and XPointer support  
some cleanup of the Makefile, autoconf and the distribution content2.2.6: Oct 25 2000:
  
Added an hash table module, migrated a number of internal structure to
    those
  
Fixed a posteriori validation problems  
HTTP module cleanups  
HTML parser improvements (tag errors, script/style handling, attribute
    normalization)
  
coalescing of adjacent text nodes  
couple of XPath bug fixes, exported the internal API2.2.5: Oct 15 2000:
  
XPointer implementation and testsuite  
Lot of XPath fixes, added variable and functions registration, more
    tests
  
Portability fixes, lots of enhancements toward an easy Windows build
    and release
  
Late validation fixes  
Integrated a lot of contributed patches  
added memory management docs  
a performance problem when using large buffer seems fixed2.2.4: Oct 1 2000:
  
main XPath problem fixed  
Integrated portability patches for Windows  
Serious bug fixes on the URI and HTML code2.2.3: Sep 17 2000
  
bug fixes  
cleanup of entity handling code  
overall review of all loops in the parsers, all sprintf usage has been
    checked too
  
Far better handling of larges Dtd. Validating against DocBook XML Dtd
    works smoothly now.
1.8.10: Sep 6 2000
  
bug fix release for some Gnome projects2.2.2: August 12 2000
  
mostly bug fixes  
started adding routines to access xml parser context options2.2.1: July 21 2000
  
a purely bug fixes release  
fixed an encoding support problem when parsing from a memory block  
fixed a DOCTYPE parsing problem  
removed a bug in the function allowing to override the memory
    allocation routines
2.2.0: July 14 2000
  
applied a lot of portability fixes  
better encoding support/cleanup and saving (content is now always
    encoded in UTF-8)
  
the HTML parser now correctly handles encodings  
added xmlHasProp()  
fixed a serious problem with &#38;  
propagated the fix to FTP client  
cleanup, bugfixes, etc ...  
Added a page about encoding.htmllibxml Internationalization
    support
1.8.9:  July 9 2000
  
fixed the spec the RPMs should be better  
fixed a serious bug in the FTP implementation, released 1.8.9 to solve
    rpmfind users problem
2.1.1: July 1 2000
  
fixes a couple of bugs in the 2.1.0 packaging  
improvements on the HTML parser2.1.0 and 1.8.8: June 29 2000
  
1.8.8 is mostly a commodity package for upgrading to libxml2 according
    to 
upgrade.htmlnew instructions . It fixes a nasty problem
    about &#38; charref parsing
  
2.1.0 also ease the upgrade from libxml v1 to the recent version. it
    also contains numerous fixes and enhancements:
    
      
added xmlStopParser() to stop parsing      
improved a lot parsing speed when there is large CDATA blocs      
includes XPath patches provided by Picdar Technology      
tried to fix as much as possible DTD validation and namespace
        related problems
      
output to a given encoding has been added/tested      
lot of various fixes    
  
2.0.0: Apr 12 2000
  
First public release of libxml2. If you are using libxml, it's a good
    idea to check the 1.x to 2.x upgrade instructions. NOTE: while initially
    scheduled for Apr 3 the release occurred only on Apr 12 due to massive
    workload.
  
The include are now located under $prefix/include/libxml (instead of
    $prefix/include/gnome-xml), they also are referenced by
    
#include <libxml/xxx.h>    
instead of
    
#include "xxx.h"  
  
a new URI module for parsing URIs and following strictly RFC 2396  
the memory allocation routines used by libxml can now be overloaded
    dynamically by using xmlMemSetup()
  
The previously CVS only tool tester has been renamed
    
xmllint and is now installed as part of the libxml2
    package
  
The I/O interface has been revamped. There is now ways to plug in
    specific I/O modules, either at the URI scheme detection level using
    xmlRegisterInputCallbacks()  or by passing I/O functions when creating a
    parser context using xmlCreateIOParserCtxt()
  
there is a C preprocessor macro LIBXML_VERSION providing the version
    number of the libxml module in use
  
a number of optional features of libxml can now be excluded at
    configure time (FTP/HTTP/HTML/XPath/Debug)
2.0.0beta: Mar 14 2000
  
This is a first Beta release of libxml version 2  
It's available only from ftp://xmlsoft.org/xmlsoft.org
    FTP
, it's packaged as libxml2-2.0.0beta and available as tar and
  RPMs
  
This version is now the head in the Gnome CVS base, the old one is
    available under the tag LIB_XML_1_X
  
This includes a very large set of changes. From a  programmatic point
    of view applications should not have to be modified too much, check the
    
upgrade.htmlupgrade page   
Some interfaces may changes (especially a bit about encoding).  
the updates includes:
    
      
fix I18N support. ISO-Latin-x/UTF-8/UTF-16 (nearly) seems correctly
        handled now
      
Better handling of entities, especially well-formedness checking
        and proper PEref extensions in external subsets
      
DTD conditional sections      
Validation now correctly handle entities content      
http://rpmfind.net/tools/gdome/messages/0039.htmlchange
        structures to accommodate DOM
    
  
  
Serious progress were made toward compliance, conf/result.htmlhere are the result of the test  against the
    OASIS testsuite (except the Japanese tests since I don't support that
    encoding yet). This URL is rebuilt every couple of hours using the CVS
    head version.
1.8.7: Mar 6 2000
  
This is a bug fix release:  
It is possible to disable the ignorable blanks heuristic used by
    libxml-1.x, a new function  xmlKeepBlanksDefault(0) will allow this. Note
    that for adherence to XML spec, this behaviour will be disabled by
    default in 2.x . The same function will allow to keep compatibility for
    old code.
  
Blanks in <a>  </a> constructs are not ignored anymore,
    avoiding heuristic is really the Right Way :-\
  
The unchecked use of snprintf which was breaking libxml-1.8.6
    compilation on some platforms has been fixed
  
nanoftp.c nanohttp.c: Fixed '#' and '?' stripping when processing
  URIs
1.8.6: Jan 31 2000
  
added a nanoFTP transport module, debugged until the new version of http://rpmfind.net/linux/rpm2html/rpmfind.htmlrpmfind  can use
    it without troubles
1.8.5: Jan 21 2000
  
adding APIs to parse a well balanced chunk of XML (production http://www.w3.org/TR/REC-xml#NT-content[43] content  of the
    XML spec)
  
fixed a hideous bug in xmlGetProp pointed by Rune.Djurhuus@fast.no  
Jody Goldberg <jgoldberg@home.com> provided another patch trying
    to solve the zlib checks problems
  
The current state in gnome CVS base is expected to ship as 1.8.5 with
    gnumeric soon
1.8.4: Jan 13 2000
  
bug fixes, reintroduced xmlNewGlobalNs(), fixed xmlNewNs()  
all exit() call should have been removed from libxml  
fixed a problem with INCLUDE_WINSOCK on WIN32 platform  
added newDocFragment()1.8.3: Jan 5 2000
  
a Push interface for the XML and HTML parsers  
a shell-like interface to the document tree (try tester --shell :-)  
lots of bug fixes and improvement added over XMas holidays  
fixed the DTD parsing code to work with the xhtml DTD  
added xmlRemoveProp(), xmlRemoveID() and xmlRemoveRef()  
Fixed bugs in xmlNewNs()  
External entity loading code has been revamped, now it uses
    xmlLoadExternalEntity(), some fix on entities processing were added
  
cleaned up WIN32 includes of socket stuff1.8.2: Dec 21 1999
  
I got another problem with includes and C++, I hope this issue is fixed
    for good this time
  
Added a few tree modification functions: xmlReplaceNode,
    xmlAddPrevSibling, xmlAddNextSibling, xmlNodeSetName and
    xmlDocSetRootElement
  
Tried to improve the HTML output with help from mailto:clahey@umich.eduChris Lahey 1.8.1: Dec 18 1999
  
various patches to avoid troubles when using libxml with C++ compilers
    the "namespace" keyword and C escaping in include files
  
a problem in one of the core macros IS_CHAR was corrected  
fixed a bug introduced in 1.8.0 breaking default namespace processing,
    and more specifically the Dia application
  
fixed a posteriori validation (validation after parsing, or by using a
    Dtd not specified in the original document)
  
fixed a bug in1.8.0: Dec 12 1999
  
cleanup, especially memory wise  
the parser should be more reliable, especially the HTML one, it should
    not crash, whatever the input !
  
Integrated various patches, especially a speedup improvement for large
    dataset from 
mailto:cnygard@bellatlantic.netCarl Nygard ,
    configure with --with-buffers to enable them.
  
attribute normalization, oops should have been added long ago !  
attributes defaulted from DTDs should be available, xmlSetProp() now
    does entities escaping by default.
1.7.4: Oct 25 1999
  
Lots of HTML improvement  
Fixed some errors when saving both XML and HTML  
More examples, the regression tests should now look clean  
Fixed a bug with contiguous charref1.7.3: Sep 29 1999
  
portability problems fixed  
snprintf was used unconditionally, leading to link problems on system
    were it's not available, fixed
1.7.1: Sep 24 1999
  
The basic type for strings manipulated by libxml has been renamed in
    1.7.1 from 
CHAR to xmlChar. The reason
    is that CHAR was conflicting with a predefined type on Windows. However
    on non WIN32 environment, compatibility is provided by the way of  a
    
#define .  
Changed another error : the use of a structure field called errno, and
    leading to troubles on platforms where it's a macro
1.7.0: Sep 23 1999
  
Added the ability to fetch remote DTD or parsed entities, see the html/libxml-nanohttp.htmlnanohttp  module.  
Added an errno to report errors by another mean than a simple printf
    like callback
  
Finished ID/IDREF support and checking when validation  
Serious memory leaks fixed (there is now a html/libxml-xmlmemory.htmlmemory wrapper  module)  
Improvement of http://www.w3.org/TR/xpathXPath     implementation
  
Added an HTML parser front-end XML 
http://www.w3.org/TR/REC-xmlXML is a standard  for
markup-based structured documents. Here is 
an example XML
document
:
<?xml version="1.0"?>
<EXAMPLE prop1="gnome is great" prop2="&amp; linux too">
  <head>
   <title>Welcome to Gnome</title>
  </head>
  <chapter>
   <title>The Linux adventure</title>
   <p>bla bla bla ...</p>
   <image href="linus.gif"/>
   <p>...</p>
  </chapter>
</EXAMPLE>
The first line specifies that it is an XML document and gives useful
information about its encoding.  Then the rest of the document is a text
format whose structure is specified by tags between brackets. 
Each
tag opened has to be closed
. XML is pedantic about this. However, if
a tag is empty (no content), a single tag can serve as both the opening and
closing tag if it ends with 
/> rather than with
>. Note that, for example, the image tag has no content (just
an attribute) and is closed by ending the tag with 
/>.
XML can be applied successfully to a wide range of tasks, ranging from
long term structured document maintenance (where it follows the steps of
SGML) to simple data encoding mechanisms like configuration file formatting
(glade), spreadsheets (gnumeric), or even shorter lived documents such as
WebDAV where it is used to encode remote calls between a client and a
server.
XSLT 
Check http://xmlsoft.org/XSLTthe separate libxslt page 
http://www.w3.org/TR/xsltXSL Transformations ,  is a
language for transforming XML documents into other XML documents (or
HTML/textual output).
A separate library called libxslt is available implementing XSLT-1.0 for
libxml2. This module "libxslt" too can be found in the Gnome CVS base.
You can check the progresses on the libxslt http://xmlsoft.org/XSLT/ChangeLog.htmlChangelog .
Python and bindings 
There are a number of language bindings and wrappers available for
libxml2, the list below is not exhaustive. Please contact the 
http://mail.gnome.org/mailman/listinfo/xml-bindingsxml-bindings@gnome.org (
http://mail.gnome.org/archives/xml-bindings/archives ) in
order to get updates to this list or to discuss the specific topic of libxml2
or libxslt wrappers or bindings:
  
http://libxmlplusplus.sourceforge.net/Libxml++  seems the
    most up-to-date C++ bindings for libxml2, check the 
http://libxmlplusplus.sourceforge.net/reference/html/hierarchy.htmldocumentation     and the 
http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/libxmlplusplus/libxml++/examples/examples .  
There is another http://libgdome-cpp.berlios.de/C++ wrapper
    based on the gdome2 bindings
 maintained by Tobias Peters.  
and a third C++ wrapper by Peter Jones <pjones@pmade.org>
    
Website: http://pmade.org/pjones/software/xmlwrapp/http://pmade.org/pjones/software/xmlwrapp/ 
  
  
http://mail.gnome.org/archives/xml/2001-March/msg00014.htmlMatt
    Sergeant
 developed http://axkit.org/download/XML::LibXSLT , a Perl wrapper for
    libxml2/libxslt as part of the 
http://axkit.com/AxKit XML
    application server
.  
If you're interested into scripting XML processing, have a look at http://xsh.sourceforge.net/XSH  an XML editing shell based on
    Libxml2 Perl bindings.
  
mailto:dkuhlman@cutter.rexx.comDave Kuhlman  provides an
    earlier version of the libxml/libxslt 
http://www.rexx.com/~dkuhlmanwrappers for Python .  
Gopal.V and Peter Minten develop http://savannah.gnu.org/projects/libxmlsharplibxml# , a set of
    C# libxml2 bindings.
  
Petr Kozelka provides http://sourceforge.net/projects/libxml2-pasPascal units to glue
    libxml2
 with Kylix, Delphi and other Pascal compilers.  
Uwe Fechner also provides http://sourceforge.net/projects/idom2-pas/idom2 , a DOM2
    implementation for Kylix2/D5/D6 from Borland.
  
There is http://rubyforge.org/projects/xml-tools/bindings
    for Ruby
  and libxml2 bindings are also available in Ruby through the
    
http://libgdome-ruby.berlios.de/libgdome-ruby  module
    maintained by Tobias Peters.
  
Steve Ball and contributors maintains http://tclxml.sourceforge.net/libxml2 and libxslt bindings for
    Tcl
.  
libxml2 and libxslt is the default XML library for PHP5.  
http://savannah.gnu.org/projects/classpathx/LibxmlJ  is
    an effort to create a 100% JAXP-compatible Java wrapper for libxml2 and
    libxslt as part of GNU ClasspathX project.
  
Patrick McPhee provides Rexx bindings fof libxml2 and libxslt, look for
    
http://www.interlog.com/~ptjm/software.htmlRexxXML .  
http://www.satimage.fr/software/en/xml_suite.htmlSatimage     provides 
http://www.satimage.fr/software/en/downloads_osaxen.htmlXMLLib
    osax
. This is an osax for Mac OS X with a set of commands to
    implement in AppleScript the XML DOM, XPATH and XSLT. Also includes
    commands for Property-lists (Apple's fast lookup table XML format.)
  
Francesco Montorsi developped https://sourceforge.net/project/showfiles.php?group_id=51305&package_id=45182wxXml2     wrappers that interface libxml2, allowing wxWidgets applications to
    load/save/edit XML instances.
The distribution includes a set of Python bindings, which are guaranteed
to be maintained as part of the library in the future, though the Python
interface have not yet reached the completeness of the C API.
Note that some of the Python purist dislike the default set of Python
bindings, rather than complaining I suggest they have a look at 
http://codespeak.net/lxml/lxml the more pythonic bindings for libxml2
and libxslt
 and http://codespeak.net/mailman/listinfo/lxml-devhelp Martijn
Faassen
 complete those.
mailto:stephane.bidoul@softwareag.comStphane Bidoul maintains 
http://users.skynet.be/sbi/libxml-python/a Windows port
of the Python bindings
.
Note to people interested in building bindings, the API is formalized as
libxml2-api.xmlan XML API description file  which allows to
automate a large part of the Python bindings, this includes function
descriptions, enums, structures, typedefs, etc... The Python script used to
build the bindings is python/generator.py in the source distribution.
To install the Python bindings there are 2 options:
  
If you use an RPM based distribution, simply install the http://rpmfind.net/linux/rpm2html/search.php?query=libxml2-pythonlibxml2-python
    RPM
 (and if needed the http://rpmfind.net/linux/rpm2html/search.php?query=libxslt-pythonlibxslt-python
    RPM
).  
Otherwise use the ftp://xmlsoft.org/python/libxml2-python
    module distribution
 corresponding to your installed version of
    libxml2 and libxslt. Note that to install it you will need both libxml2
    and libxslt installed and run "python setup.py build install" in the
    module tree.
The distribution includes a set of examples and regression tests for the
python bindings in the 
python/tests directory. Here are some
excerpts from those tests:
tst.py:
This is a basic test of the file interface and DOM navigation:
import libxml2, sys
doc = libxml2.parseFile("tst.xml")
if doc.name != "tst.xml":
    print "doc.name failed"
    sys.exit(1)
root = doc.children
if root.name != "doc":
    print "root.name failed"
    sys.exit(1)
child = root.children
if child.name != "foo":
    print "child.name failed"
    sys.exit(1)
doc.freeDoc()
The Python module is called libxml2; parseFile is the equivalent of
xmlParseFile (most of the bindings are automatically generated, and the xml
prefix is removed and the casing convention are kept). All node seen at the
binding level share the same subset of accessors:
  
name : returns the node name  
type : returns a string indicating the node type  
content : returns the content of the node, it is based on
    xmlNodeGetContent() and hence is recursive.
  
parent , children, last,
    
next, prev, doc,
    
properties: pointing to the associated element in the tree,
    those may return None in case no such link exists.
Also note the need to explicitly deallocate documents with freeDoc() .
Reference counting for libxml2 trees would need quite a lot of work to
function properly, and rather than risk memory leaks if not implemented
correctly it sounds safer to have an explicit function to free a tree. The
wrapper python objects like doc, root or child are them automatically garbage
collected.
validate.py:
This test check the validation interfaces and redirection of error
messages:
import libxml2
#deactivate error messages from the validation
def noerr(ctx, str):
    pass
libxml2.registerErrorHandler(noerr, None)
ctxt = libxml2.createFileParserCtxt("invalid.xml")
ctxt.validate(1)
ctxt.parseDocument()
doc = ctxt.doc()
valid = ctxt.isValid()
doc.freeDoc()
if valid != 0:
    print "validity check failed"
The first thing to notice is the call to registerErrorHandler(), it
defines a new error handler global to the library. It is used to avoid seeing
the error messages when trying to validate the invalid document.
The main interest of that test is the creation of a parser context with
createFileParserCtxt() and how the behaviour can be changed before calling
parseDocument() . Similarly the informations resulting from the parsing phase
are also available using context methods.
Contexts like nodes are defined as class and the libxml2 wrappers maps the
C function interfaces in terms of objects method as much as possible. The
best to get a complete view of what methods are supported is to look at the
libxml2.py module containing all the wrappers.
push.py:
This test show how to activate the push parser interface:
import libxml2
ctxt = libxml2.createPushParser(None, "<foo", 4, "test.xml")
ctxt.parseChunk("/>", 2, 1)
doc = ctxt.doc()
doc.freeDoc()
The context is created with a special call based on the
xmlCreatePushParser() from the C library. The first argument is an optional
SAX callback object, then the initial set of data, the length and the name of
the resource in case URI-References need to be computed by the parser.
Then the data are pushed using the parseChunk() method, the last call
setting the third argument terminate to 1.
pushSAX.py:
this test show the use of the event based parsing interfaces. In this case
the parser does not build a document, but provides callback information as
the parser makes progresses analyzing the data being provided:
import libxml2
log = ""
class callback:
    def startDocument(self):
        global log
        log = log + "startDocument:"
    def endDocument(self):
        global log
        log = log + "endDocument:"
    def startElement(self, tag, attrs):
        global log
        log = log + "startElement %s %s:" % (tag, attrs)
    def endElement(self, tag):
        global log
        log = log + "endElement %s:" % (tag)
    def characters(self, data):
        global log
        log = log + "characters: %s:" % (data)
    def warning(self, msg):
        global log
        log = log + "warning: %s:" % (msg)
    def error(self, msg):
        global log
        log = log + "error: %s:" % (msg)
    def fatalError(self, msg):
        global log
        log = log + "fatalError: %s:" % (msg)
handler = callback()
ctxt = libxml2.createPushParser(handler, "<foo", 4, "test.xml")
chunk = " url='tst'>b"
ctxt.parseChunk(chunk, len(chunk), 0)
chunk = "ar</foo>"
ctxt.parseChunk(chunk, len(chunk), 1)
reference = "startDocument:startElement foo {'url': 'tst'}:" + \ 
            "characters: bar:endElement foo:endDocument:"
if log != reference:
    print "Error got: %s" % log
    print "Expected: %s" % reference
The key object in that test is the handler, it provides a number of entry
points which can be called by the parser as it makes progresses to indicate
the information set obtained. The full set of callback is larger than what
the callback class in that specific example implements (see the SAX
definition for a complete list). The wrapper will only call those supplied by
the object when activated. The startElement receives the names of the element
and a dictionary containing the attributes carried by this element.
Also note that the reference string generated from the callback shows a
single character call even though the string "bar" is passed to the parser
from 2 different call to parseChunk()
xpath.py:
This is a basic test of XPath wrappers support
import libxml2
doc = libxml2.parseFile("tst.xml")
ctxt = doc.xpathNewContext()
res = ctxt.xpathEval("//*")
if len(res) != 2:
    print "xpath query: wrong node set size"
    sys.exit(1)
if res[0].name != "doc" or res[1].name != "foo":
    print "xpath query: wrong node set value"
    sys.exit(1)
doc.freeDoc()
ctxt.xpathFreeContext()
This test parses a file, then create an XPath context to evaluate XPath
expression on it. The xpathEval() method execute an XPath query and returns
the result mapped in a Python way. String and numbers are natively converted,
and node sets are returned as a tuple of libxml2 Python nodes wrappers. Like
the document, the XPath context need to be freed explicitly, also not that
the result of the XPath query may point back to the document tree and hence
the document must be freed after the result of the query is used.
xpathext.py:
This test shows how to extend the XPath engine with functions written in
python:
import libxml2
def foo(ctx, x):
    return x + 1
doc = libxml2.parseFile("tst.xml")
ctxt = doc.xpathNewContext()
libxml2.registerXPathFunction(ctxt._o, "foo", None, foo)
res = ctxt.xpathEval("foo(1)")
if res != 2:
    print "xpath extension failure"
doc.freeDoc()
ctxt.xpathFreeContext()
Note how the extension function is registered with the context (but that
part is not yet finalized, this may change slightly in the future).
tstxpath.py:
This test is similar to the previous one but shows how the extension
function can access the XPath evaluation context:
def foo(ctx, x):
    global called
    #
    # test that access to the XPath evaluation contexts
    #
    pctxt = libxml2.xpathParserContext(_obj=ctx)
    ctxt = pctxt.context()
    called = ctxt.function()
    return x + 1
All the interfaces around the XPath parser(or rather evaluation) context
are not finalized, but it should be sufficient to do contextual work at the
evaluation point.
Memory debugging:
last but not least, all tests starts with the following prologue:
#memory debug specific
libxml2.debugMemory(1)
and ends with the following epilogue:
#memory debug specific
libxml2.cleanupParser()
if libxml2.debugMemory(1) == 0:
    print "OK"
else:
    print "Memory leak %d bytes" % (libxml2.debugMemory(1))
    libxml2.dumpMemory()
Those activate the memory debugging interface of libxml2 where all
allocated block in the library are tracked. The prologue then cleans up the
library state and checks that all allocated memory has been freed. If not it
calls dumpMemory() which saves that list in a 
.memdump file.
libxml2 architecture 
Libxml2 is made of multiple components; some of them are optional, and
most of the block interfaces are public. The main components are:
  
an Input/Output layer  
FTP and HTTP client layers (optional)  
an Internationalization layer managing the encodings support  
a URI module  
the XML parser and its basic SAX interface  
an HTML parser using the same SAX interface (optional)  
a SAX tree module to build an in-memory DOM representation  
a tree module to manipulate the DOM representation  
a validation module using the DOM representation (optional)  
an XPath module for global lookup in a DOM representation
  (optional)
  
a debug module (optional)Graphically this gives the following:
a graphical view of the various
The tree output 
The parser returns a tree built during the document analysis. The value
returned is an 
xmlDocPtr (i.e., a pointer to an
xmlDoc structure). This structure contains information such
as the file name, the document type, and a 
children pointer
which is the root of the document (or more exactly the first child under the
root which is the document). The tree is made of 
xmlNodes,
chained in double-linked lists of siblings and with a children<->parent
relationship. An xmlNode can also carry properties (a chain of xmlAttr
structures). An attribute may have a value which is a list of TEXT or
ENTITY_REF nodes.
Here is an example (erroneous with respect to the XML spec since there
should be only one ELEMENT under the root):
 structure.gif 
In the source package there is a small program (not installed by default)
called 
xmllint which parses XML files given as argument and
prints them back as parsed. This is useful for detecting errors both in XML
code and in the XML parser itself. It has an option 
--debugwhich prints the actual in-memory structure of the document; here is the
result with the 
#exampleexample  given before:
DOCUMENT
version=1.0
standalone=true
  ELEMENT EXAMPLE
    ATTRIBUTE prop1
      TEXT
      content=gnome is great
    ATTRIBUTE prop2
      ENTITY_REF
      TEXT
      content= linux too 
    ELEMENT head
      ELEMENT title
        TEXT
        content=Welcome to Gnome
    ELEMENT chapter
      ELEMENT title
        TEXT
        content=The Linux adventure
      ELEMENT p
        TEXT
        content=bla bla bla ...
      ELEMENT image
        ATTRIBUTE href
          TEXT
          content=linus.gif
      ELEMENT p
        TEXT
        content=...
This should be useful for learning the internal representation model.
The SAX interface 
Sometimes the DOM tree output is just too large to fit reasonably into
memory. In that case (and if you don't expect to save back the XML document
loaded using libxml), it's better to use the SAX interface of libxml. SAX is
a 
callback-based interface to the parser. Before parsing,
the application layer registers a customized set of callbacks which are
called by the library as it progresses through the XML input.
To get more detailed step-by-step guidance on using the SAX interface of
libxml, see the 
http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.htmlnice
documentation
.written by mailto:james@daa.com.auJames
Henstridge
.
You can debug the SAX behaviour by using the testSAXprogram located in the gnome-xml module (it's usually not shipped in the
binary packages of libxml, but you can find it in the tar source
distribution). Here is the sequence of callbacks that would be reported by
testSAX when parsing the example XML document shown earlier:
SAX.setDocumentLocator()
SAX.startDocument()
SAX.getEntity(amp)
SAX.startElement(EXAMPLE, prop1='gnome is great', prop2='&amp; linux too')
SAX.characters(   , 3)
SAX.startElement(head)
SAX.characters(    , 4)
SAX.startElement(title)
SAX.characters(Welcome to Gnome, 16)
SAX.endElement(title)
SAX.characters(   , 3)
SAX.endElement(head)
SAX.characters(   , 3)
SAX.startElement(chapter)
SAX.characters(    , 4)
SAX.startElement(title)
SAX.characters(The Linux adventure, 19)
SAX.endElement(title)
SAX.characters(    , 4)
SAX.startElement(p)
SAX.characters(bla bla bla ..., 15)
SAX.endElement(p)
SAX.characters(    , 4)
SAX.startElement(image, href='linus.gif')
SAX.endElement(image)
SAX.characters(    , 4)
SAX.startElement(p)
SAX.characters(..., 3)
SAX.endElement(p)
SAX.characters(   , 3)
SAX.endElement(chapter)
SAX.characters( , 1)
SAX.endElement(EXAMPLE)
SAX.endDocument()
Most of the other interfaces of libxml2 are based on the DOM tree-building
facility, so nearly everything up to the end of this document presupposes the
use of the standard DOM tree build. Note that the DOM tree itself is built by
a set of registered default callbacks, without internal specific
interface.
Validation & DTDs 
Table of Content:
  
#General5General overview   
#definitionThe definition   
#SimpleSimple rules     
      
#referenceHow to reference a DTD from a document       
#DeclaringDeclaring elements       
#Declaring1Declaring attributes     
  
  
#SomeSome examples   
#validateHow to validate   
#OtherOther resources General overview 
Well what is validation and what is a DTD ?
DTD is the acronym for Document Type Definition. This is a description of
the content for a family of XML files. This is part of the XML 1.0
specification, and allows one to describe and verify that a given document
instance conforms to the set of rules detailing its structure and content.
Validation is the process of checking a document against a DTD (more
generally against a set of construction rules).
The validation process and building DTDs are the two most difficult parts
of the XML life cycle. Briefly a DTD defines all the possible elements to be
found within your document, what is the formal shape of your document tree
(by defining the allowed content of an element; either text, a regular
expression for the allowed list of children, or mixed content i.e. both text
and children). The DTD also defines the valid attributes for all elements and
the types of those attributes.
The definition 
The http://www.w3.org/TR/REC-xmlW3C XML Recommendation  ( http://www.xml.com/axml/axml.htmlTim Bray's annotated version of
Rev1
):
  
http://www.w3.org/TR/REC-xml#elemdeclsDeclaring
  elements
  
http://www.w3.org/TR/REC-xml#attdeclsDeclaring
  attributes
(unfortunately) all this is inherited from the SGML world, the syntax is
ancient...
Simple rules 
Writing DTDs can be done in many ways. The rules to build them if you need
something permanent or something which can evolve over time can be radically
different. Really complex DTDs like DocBook ones are flexible but quite
harder to design. I will just focus on DTDs for a formats with a fixed simple
structure. It is just a set of basic rules, and definitely not exhaustive nor
usable for complex DTD design.
How to reference a DTD from a document :
Assuming the top element of the document is spec and the dtd
is placed in the file 
mydtd in the subdirectory
dtds of the directory from where the document were loaded:
<!DOCTYPE spec SYSTEM "dtds/mydtd">
Notes:
  
The system string is actually an URI-Reference (as defined in http://www.ietf.org/rfc/rfc2396.txtRFC 2396 ) so you can use a
    full URL string indicating the location of your DTD on the Web. This is a
    really good thing to do if you want others to validate your document.
  
It is also possible to associate a PUBLIC identifier (a
    magic string) so that the DTD is looked up in catalogs on the client side
    without having to locate it on the web.
  
A DTD contains a set of element and attribute declarations, but they
    don't define what the root of the document should be. This is explicitly
    told to the parser/validator as the first element of the
    
DOCTYPE declaration. Declaring elements :
The following declares an element spec:
<!ELEMENT spec (front, body, back?)>
It also expresses that the spec element contains one front,
one 
body and one optional back children elements in
this order. The declaration of one element of the structure and its content
are done in a single declaration. Similarly the following declares
div1 elements:
<!ELEMENT div1 (head, (p | list | note)*, div2?)>
which means div1 contains one head then a series of optional
p, lists and notes and then an
optional 
div2. And last but not least an element can contain
text:
<!ELEMENT b (#PCDATA)>
b contains text or being of mixed content (text and elements
in no particular order):
<!ELEMENT p (#PCDATA|a|ul|b|i|em)*>
p can contain text or a, ul,
b, i or em elements in no particular
order.
Declaring attributes :
Again the attributes declaration includes their content definition:
<!ATTLIST termdef name CDATA #IMPLIED>
means that the element termdef can have a nameattribute containing text (
CDATA) and which is optional
(
#IMPLIED). The attribute value can also be defined within a
set:
<!ATTLIST list type (bullets|ordered|glossary)
"ordered">
means list element have a type attribute with 3
allowed values "bullets", "ordered" or "glossary" and which default to
"ordered" if the attribute is not explicitly specified.
The content type of an attribute can be text (CDATA),
anchor/reference/references
(
ID/IDREF/IDREFS), entity(ies)
(
ENTITY/ENTITIES) or name(s)
(
NMTOKEN/NMTOKENS). The following defines that a
chapter element can have an optional id attribute
of type 
ID, usable for reference from attribute of type
IDREF:
<!ATTLIST chapter id ID #IMPLIED>
The last value of an attribute definition can be #REQUIRED
meaning that the attribute has to be given, #IMPLIEDmeaning that it is optional, or the default value (possibly prefixed by
#FIXED if it is the only allowed).
Notes:
  
Usually the attributes pertaining to a given element are declared in a
    single expression, but it is just a convention adopted by a lot of DTD
    writers:
    
<!ATTLIST termdef
          id      ID      #REQUIRED
          name    CDATA   #IMPLIED>
    
The previous construct defines both id and
    
name attributes for the element termdef.
  
Some examples 
The directory test/valid/dtds/ in the libxml2 distribution
contains some complex DTD examples. The example in the file
test/valid/dia.xml shows an XML file where the simple DTD is
directly included within the document.
How to validate 
The simplest way is to use the xmllint program included with libxml. The
--valid option turns-on validation of the files given as input.
For example the following validates a copy of the first revision of the XML
1.0 specification:
xmllint --valid --noout test/valid/REC-xml-19980210.xml
the -- noout is used to disable output of the resulting tree.
The --dtdvalid dtd allows validation of the document(s)
against a given DTD.
Libxml2 exports an API to handle DTDs and validation, check the http://xmlsoft.org/html/libxml-valid.htmlassociated
description
.
Other resources 
DTDs are as old as SGML. So there may be a number of examples on-line, I
will just list one for now, others pointers welcome:
  
http://www.xml101.com:8081/dtd/XML-101 DTD I suggest looking at the examples found under test/valid/dtd and any of
the large number of books available on XML. The dia example in test/valid
should be both simple and complete enough to allow you to build your own.
Memory Management 
Table of Content:
  
#General3General overview   
#settingSetting libxml2 set of memory routines   
#cleanupCleaning up after parsing   
#DebuggingDebugging routines   
#General4General memory requirements General overview 
The module http://xmlsoft.org/html/libxml-xmlmemory.htmlxmlmemory.h provides the interfaces to the libxml2 memory system:
  
libxml2 does not use the libc memory allocator directly but xmlFree(),
    xmlMalloc() and xmlRealloc()
  
those routines can be reallocated to a specific set of routine, by
    default the libc ones i.e. free(), malloc() and realloc()
  
the xmlmemory.c module includes a set of debugging routine Setting libxml2 set of memory routines 
It is sometimes useful to not use the default memory allocator, either for
debugging, analysis or to implement a specific behaviour on memory management
(like on embedded systems). Two function calls are available to do so:
  
http://xmlsoft.org/html/libxml-xmlmemory.htmlxmlMemGet
    ()
 which return the current set of functions in use by the parser  
http://xmlsoft.org/html/libxml-xmlmemory.htmlxmlMemSetup()     which allow to set up a new set of memory allocation functions
Of course a call to xmlMemSetup() should probably be done before calling
any other libxml2 routines (unless you are sure your allocations routines are
compatibles).
Cleaning up after parsing 
Libxml2 is not stateless, there is a few set of memory structures needing
allocation before the parser is fully functional (some encoding structures
for example). This also mean that once parsing is finished there is a tiny
amount of memory (a few hundred bytes) which can be recollected if you don't
reuse the parser immediately:
  
http://xmlsoft.org/html/libxml-parser.htmlxmlCleanupParser
    ()
 is a centralized routine to free the parsing states. Note that it
    won't deallocate any produced tree if any (use the xmlFreeDoc() and
    related routines for this).
  
http://xmlsoft.org/html/libxml-parser.htmlxmlInitParser
    ()
 is the dual routine allowing to preallocate the parsing state
    which can be useful for example to avoid initialization reentrancy
    problems when using libxml2 in multithreaded applications
Generally xmlCleanupParser() is safe, if needed the state will be rebuild
at the next invocation of parser routines, but be careful of the consequences
in multithreaded applications.
Debugging routines 
When configured using --with-mem-debug flag (off by default), libxml2 uses
a set of memory allocation debugging routines keeping track of all allocated
blocks and the location in the code where the routine was called. A couple of
other debugging routines allow to dump the memory allocated infos to a file
or call a specific routine when a given block number is allocated:
  
http://xmlsoft.org/html/libxml-xmlmemory.htmlxmlMallocLoc()     
http://xmlsoft.org/html/libxml-xmlmemory.htmlxmlReallocLoc()     and 
http://xmlsoft.org/html/libxml-xmlmemory.htmlxmlMemStrdupLoc()     are the memory debugging replacement allocation routines
  
http://xmlsoft.org/html/libxml-xmlmemory.htmlxmlMemoryDump
    ()
 dumps all the informations about the allocated memory block lefts
    in the 
.memdump fileWhen developing libxml2 memory debug is enabled, the tests programs call
xmlMemoryDump () and the "make test" regression tests will check for any
memory leak during the full regression test sequence, this helps a lot
ensuring that libxml2  does not leak memory and bullet proof memory
allocations use (some libc implementations are known to be far too permissive
resulting in major portability problems!).
If the .memdump reports a leak, it displays the allocation function and
also tries to give some informations about the content and structure of the
allocated blocks left. This is sufficient in most cases to find the culprit,
but not always. Assuming the allocation problem is reproducible, it is
possible to find more easily:
  
write down the block number xxxx not allocated  
export the environment variable XML_MEM_BREAKPOINT=xxxx , the easiest
    when using GDB is to simply give the command
    
set environment XML_MEM_BREAKPOINT xxxx
    
before running the program.
  
  
run the program under a debugger and set a breakpoint on
    xmlMallocBreakpoint() a specific function called when this precise block
    is allocated
  
when the breakpoint is reached you can then do a fine analysis of the
    allocation an step  to see the condition resulting in the missing
    deallocation.
I used to use a commercial tool to debug libxml2 memory problems but after
noticing that it was not detecting memory leaks that simple mechanism was
used and proved extremely efficient until now. Lately I have also used 
http://developer.kde.org/~sewardj/valgrind  with quite some
success, it is tied to the i386 architecture since it works by emulating the
processor and instruction set, it is slow but  extremely efficient, i.e. it
spot memory usage errors in a very precise way.
General memory requirements 
How much libxml2 memory require ? It's hard to tell in average it depends
of a number of things:
  
the parser itself should work  in a fixed amount of memory, except for
    information maintained about the stacks of names and  entities locations.
    The I/O and encoding handlers will probably account for a few KBytes.
    This is true for both the XML and HTML parser (though the HTML parser
    need more state).
  
If you are generating the DOM tree then memory requirements will grow
    nearly linear with the size of the data. In general for a balanced
    textual document the internal memory requirement is about 4 times the
    size of the UTF8 serialization of this document (example the XML-1.0
    recommendation is a bit more of 150KBytes and takes 650KBytes of main
    memory when parsed). Validation will add a amount of memory required for
    maintaining the external Dtd state which should be linear with the
    complexity of the content model defined by the Dtd
  
If you need to work with fixed memory requirements or don't need the
    full DOM tree then using the 
xmlreader.htmlxmlReader
    interface
 is probably the best way to proceed, it still allows to
    validate or operate on subset of the tree if needed.
  
If you don't care about the advanced features of libxml2 like
    validation, DOM, XPath or XPointer, don't use entities, need to work with
    fixed memory requirements, and try to get the fastest parsing possible
    then the SAX interface should be used, but it has known restrictions.
Encodings support 
If you are not really familiar with Internationalization (usual shortcut
is I18N) , Unicode, characters and glyphs, I suggest you read a 
http://www.tbray.org/ongoing/When/200x/2003/04/06/Unicodepresentation by Tim Bray on Unicode and why you should care about it.
If you don't understand why it does not make sense to have a string
without knowing what encoding it uses
, then as Joel Spolsky said http://www.joelonsoftware.com/articles/Unicode.htmlplease do not
write another line of code until you finish reading that article.
. It is
a prerequisite to understand this page, and avoid a lot of problems with
libxml2, XML or text processing in general.
Table of Content:
  
encoding.html#WhatWhat does internationalization support
    mean ?
  
encoding.html#internalThe internal encoding, how and
  why
  
encoding.html#implementeHow is it implemented ?   
encoding.html#DefaultDefault supported encodings   
encoding.html#extendHow to extend the existing
  support
What does internationalization support mean ? 
XML was designed from the start to allow the support of any character set
by using Unicode. Any conformant XML parser has to support the UTF-8 and
UTF-16 default encodings which can both express the full unicode ranges. UTF8
is a variable length encoding whose greatest points are to reuse the same
encoding for ASCII and to save space for Western encodings, but it is a bit
more complex to handle in practice. UTF-16 use 2 bytes per character (and
sometimes combines two pairs), it makes implementation easier, but looks a
bit overkill for Western languages encoding. Moreover the XML specification
allows the document to be encoded in other encodings at the condition that
they are clearly labeled as such. For example the following is a wellformed
XML document encoded in ISO-8859-1 and using accentuated letters that we
French like for both markup and content:
<?xml version="1.0" encoding="ISO-8859-1"?>
<trs>l</trs>
Having internationalization support in libxml2 means the following:
  
the document is properly parsed  
informations about it's encoding are saved  
it can be modified  
it can be saved in its original encoding  
it can also be saved in another encoding supported by libxml2 (for
    example straight UTF8 or even an ASCII form)
Another very important point is that the whole libxml2 API, with the
exception of a few routines to read with a specific encoding or save to a
specific encoding, is completely agnostic about the original encoding of the
document.
It should be noted too that the HTML parser embedded in libxml2 now obey
the same rules too, the following document will be (as of 2.2.2) handled  in
an internationalized fashion by libxml2 too:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
                      "http://www.w3.org/TR/REC-html40/loose.dtd">
<html lang="fr">
<head>
  <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1">
</head>
<body>
<p>W3C cre des standards pour le Web.</body>
</html>
The internal encoding, how and why 
One of the core decisions was to force all documents to be converted to a
default internal encoding, and that encoding to be UTF-8, here are the
rationales for those choices:
  
keeping the native encoding in the internal form would force the libxml
    users (or the code associated) to be fully aware of the encoding of the
    original document, for examples when adding a text node to a document,
    the content would have to be provided in the document encoding, i.e. the
    client code would have to check it before hand, make sure it's conformant
    to the encoding, etc ... Very hard in practice, though in some specific
    cases this may make sense.
  
the second decision was which encoding. From the XML spec only UTF8 and
    UTF16 really makes sense as being the two only encodings for which there
    is mandatory support. UCS-4 (32 bits fixed size encoding) could be
    considered an intelligent choice too since it's a direct Unicode mapping
    support. I selected UTF-8 on the basis of efficiency and compatibility
    with surrounding software:
    
      
UTF-8 while a bit more complex to convert from/to (i.e. slightly
        more costly to import and export CPU wise) is also far more compact
        than UTF-16 (and UCS-4) for a majority of the documents I see it used
        for right now (RPM RDF catalogs, advogato data, various configuration
        file formats, etc.) and the key point for today's computer
        architecture is efficient uses of caches. If one nearly double the
        memory requirement to store the same amount of data, this will trash
        caches (main memory/external caches/internal caches) and my take is
        that this harms the system far more than the CPU requirements needed
        for the conversion to UTF-8
      
Most of libxml2 version 1 users were using it with straight ASCII
        most of the time, doing the conversion with an internal encoding
        requiring all their code to be rewritten was a serious show-stopper
        for using UTF-16 or UCS-4.
      
UTF-8 is being used as the de-facto internal encoding standard for
        related code like the 
http://www.pango.org/pango         upcoming Gnome text widget, and a lot of Unix code (yet another place
        where Unix programmer base takes a different approach from Microsoft
        - they are using UTF-16)
    
  
What does this mean in practice for the libxml2 user:
  
xmlChar, the libxml2 data type is a byte, those bytes must be assembled
    as UTF-8 valid strings. The proper way to terminate an xmlChar * string
    is simply to append 0 byte, as usual.
  
One just need to make sure that when using chars outside the ASCII set,
    the values has been properly converted to UTF-8
How is it implemented ? 
Let's describe how all this works within libxml, basically the I18N
(internationalization) support get triggered only during I/O operation, i.e.
when reading a document or saving one. Let's look first at the reading
sequence:
  
when a document is processed, we usually don't know the encoding, a
    simple heuristic allows to detect UTF-16 and UCS-4 from encodings where
    the ASCII range (0-0x7F) maps with ASCII
  
the xml declaration if available is parsed, including the encoding
    declaration. At that point, if the autodetected encoding is different
    from the one declared a call to xmlSwitchEncoding() is issued.
  
If there is no encoding declaration, then the input has to be in either
    UTF-8 or UTF-16, if it is not then at some point when processing the
    input, the converter/checker of UTF-8 form will raise an encoding error.
    You may end-up with a garbled document, or no document at all ! Example:
    
~/XML -> ./xmllint err.xml 
err.xml:1: error: Input is not proper UTF-8, indicate encoding !
<trs>l</trs>
   ^
err.xml:1: error: Bytes: 0xE8 0x73 0x3E 0x6C
<trs>l</trs>
   ^
  
  
xmlSwitchEncoding() does an encoding name lookup, canonicalize it, and
    then search the default registered encoding converters for that encoding.
    If it's not within the default set and iconv() support has been compiled
    it, it will ask iconv for such an encoder. If this fails then the parser
    will report an error and stops processing:
    
~/XML -> ./xmllint err2.xml 
err2.xml:1: error: Unsupported encoding UnsupportedEnc
<?xml version="1.0" encoding="UnsupportedEnc"?>
                                             ^
  
  
From that point the encoder processes progressively the input (it is
    plugged as a front-end to the I/O module) for that entity. It captures
    and converts on-the-fly the document to be parsed to UTF-8. The parser
    itself just does UTF-8 checking of this input and process it
    transparently. The only difference is that the encoding information has
    been added to the parsing context (more precisely to the input
    corresponding to this entity).
  
The result (when using DOM) is an internal form completely in UTF-8
    with just an encoding information on the document node.
Ok then what happens when saving the document (assuming you
collected/built an xmlDoc DOM like structure) ? It depends on the function
called, xmlSaveFile() will just try to save in the original encoding, while
xmlSaveFileTo() and xmlSaveFileEnc() can optionally save to a given
encoding:
  
if no encoding is given, libxml2 will look for an encoding value
    associated to the document and if it exists will try to save to that
    encoding,
    
otherwise everything is written in the internal form, i.e. UTF-8
  
  
so if an encoding was specified, either at the API level or on the
    document, libxml2 will again canonicalize the encoding name, lookup for a
    converter in the registered set or through iconv. If not found the
    function will return an error code
  
the converter is placed before the I/O buffer layer, as another kind of
    buffer, then libxml2 will simply push the UTF-8 serialization to through
    that buffer, which will then progressively be converted and pushed onto
    the I/O layer.
  
It is possible that the converter code fails on some input, for example
    trying to push an UTF-8 encoded Chinese character through the UTF-8 to
    ISO-8859-1 converter won't work. Since the encoders are progressive they
    will just report the error and the number of bytes converted, at that
    point libxml2 will decode the offending character, remove it from the
    buffer and replace it with the associated charRef encoding &#123; and
    resume the conversion. This guarantees that any document will be saved
    without losses (except for markup names where this is not legal, this is
    a problem in the current version, in practice avoid using non-ascii
    characters for tag or attribute names). A special "ascii" encoding name
    is used to save documents to a pure ascii form can be used when
    portability is really crucial
Here are a few examples based on the same test document:
~/XML -> ./xmllint isolat1 
<?xml version="1.0" encoding="ISO-8859-1"?>
<trs>l</trs>
~/XML -> ./xmllint --encode UTF-8 isolat1 
<?xml version="1.0" encoding="UTF-8"?>
<très>l  </très>
~/XML -> 
The same processing is applied (and reuse most of the code) for HTML I18N
processing. Looking up and modifying the content encoding is a bit more
difficult since it is located in a <meta> tag under the <head>,
so a couple of functions htmlGetMetaEncoding() and htmlSetMetaEncoding() have
been provided. The parser also attempts to switch encoding on the fly when
detecting such a tag on input. Except for that the processing is the same
(and again reuses the same code).
Default supported encodings 
libxml2 has a set of default converters for the following encodings
(located in encoding.c):
  
UTF-8 is supported by default (null handlers)  
UTF-16, both little and big endian  
ISO-Latin-1 (ISO-8859-1) covering most western languages  
ASCII, useful mostly for saving  
HTML, a specific handler for the conversion of UTF-8 to ASCII with HTML
    predefined entities like &copy; for the Copyright sign.
More over when compiled on an Unix platform with iconv support the full
set of encodings supported by iconv can be instantly be used by libxml. On a
linux machine with glibc-2.1 the list of supported encodings and aliases fill
3 full pages, and include UCS-4, the full set of ISO-Latin encodings, and the
various Japanese ones.
To convert from the UTF-8 values returned from the API to another encoding
then it is possible to use the function provided from 
html/libxml-encoding.htmlthe encoding module  like html/libxml-encoding.html#UTF8Toisolat1UTF8Toisolat1 , or use the
POSIX 
http://www.opengroup.org/onlinepubs/009695399/functions/iconv.htmliconv() API directly.
Encoding aliases
From 2.2.3, libxml2 has support to register encoding names aliases. The
goal is to be able to parse document whose encoding is supported but where
the name differs (for example from the default set of names accepted by
iconv). The following functions allow to register and handle new aliases for
existing encodings. Once registered libxml2 will automatically lookup the
aliases when handling a document:
  
int xmlAddEncodingAlias(const char *name, const char *alias);  
int xmlDelEncodingAlias(const char *alias);  
const char * xmlGetEncodingAlias(const char *alias);  
void xmlCleanupEncodingAliases(void); How to extend the existing support 
Well adding support for new encoding, or overriding one of the encoders
(assuming it is buggy) should not be hard, just write input and output
conversion routines to/from UTF-8, and register them using
xmlNewCharEncodingHandler(name, xxxToUTF8, UTF8Toxxx),  and they will be
called automatically if the parser(s) encounter such an encoding name
(register it uppercase, this will help). The description of the encoders,
their arguments and expected return values are described in the encoding.h
header.
A quick note on the topic of subverting the parser to use a different
internal encoding than UTF-8, in some case people will absolutely want to
keep the internal encoding different, I think it's still possible (but the
encoding must be compliant with ASCII on the same subrange) though I didn't
tried it. The key is to override the default conversion routines (by
registering null encoders/decoders for your charsets), and bypass the UTF-8
checking of the parser by setting the parser context charset
(ctxt->charset) to something different than XML_CHAR_ENCODING_UTF8, but
there is no guarantee that this will work. You may also have some troubles
saving back.
Basically proper I18N support is important, this requires at least
libxml-2.0.0, but a lot of features and corrections are really available only
starting 2.2.
I/O Interfaces 
Table of Content:
  
#General1General overview   
#basicThe basic buffer type   
#InputInput I/O handlers   
#OutputOutput I/O handlers   
#entitiesThe entities loader   
#Example2Example of customized I/O General overview 
The module http://xmlsoft.org/html/libxml-xmlio.htmlxmlIO.h  provides
the interfaces to the libxml2 I/O system. This consists of 4 main parts:
  
Entities loader, this is a routine which tries to fetch the entities
    (files) based on their PUBLIC and SYSTEM identifiers. The default loader
    don't look at the public identifier since libxml2 do not maintain a
    catalog. You can redefine you own entity loader by using
    
xmlGetExternalEntityLoader() and
    
xmlSetExternalEntityLoader(). #entitiesCheck the
    example
.  
Input I/O buffers which are a commodity structure used by the parser(s)
    input layer to handle fetching the informations to feed the parser. This
    provides buffering and is also a placeholder where the encoding
    converters to UTF8 are piggy-backed.
  
Output I/O buffers are similar to the Input ones and fulfill similar
    task but when generating a serialization from a tree.
  
A mechanism to register sets of I/O callbacks and associate them with
    specific naming schemes like the protocol part of the URIs.
    
This affect the default I/O operations and allows to use specific I/O
    handlers for certain names.
  
The general mechanism used when loading http://rpmfind.net/xml.html for
example in the HTML parser is the following:
  
The default entity loader calls xmlNewInputFromFile() with
    the parsing context and the URI string.
  
the URI string is checked against the existing registered handlers
    using their match() callback function, if the HTTP module was compiled
    in, it is registered and its match() function will succeeds
  
the open() function of the handler is called and if successful will
    return an I/O Input buffer
  
the parser will the start reading from this buffer and progressively
    fetch information from the resource, calling the read() function of the
    handler until the resource is exhausted
  
if an encoding change is detected it will be installed on the input
    buffer, providing buffering and efficient use of the conversion
  routines
  
once the parser has finished, the close() function of the handler is
    called once and the Input buffer and associated resources are
  deallocated.
The user defined callbacks are checked first to allow overriding of the
default libxml2 I/O routines.
The basic buffer type 
All the buffer manipulation handling is done using the
xmlBuffer type define in http://xmlsoft.org/html/libxml-tree.htmltree.h  which is a
resizable memory buffer. The buffer allocation strategy can be selected to be
either best-fit or use an exponential doubling one (CPU vs. memory use
trade-off). The values are 
XML_BUFFER_ALLOC_EXACT and
XML_BUFFER_ALLOC_DOUBLEIT, and can be set individually or on a
system wide basis using 
xmlBufferSetAllocationScheme(). A number
of functions allows to manipulate buffers with names starting with the
xmlBuffer... prefix.
Input I/O handlers 
An Input I/O handler is a simple structure
xmlParserInputBuffer containing a context associated to the
resource (file descriptor, or pointer to a protocol handler), the read() and
close() callbacks to use and an xmlBuffer. And extra xmlBuffer and a charset
encoding handler are also present to support charset conversion when
needed.
Output I/O handlers 
An Output handler xmlOutputBuffer is completely similar to an
Input one except the callbacks are write() and close().
The entities loader 
The entity loader resolves requests for new entities and create inputs for
the parser. Creating an input from a filename or an URI string is done
through the xmlNewInputFromFile() routine.  The default entity loader do not
handle the PUBLIC identifier associated with an entity (if any). So it just
calls xmlNewInputFromFile() with the SYSTEM identifier (which is mandatory in
XML).
If you want to hook up a catalog mechanism then you simply need to
override the default entity loader, here is an example:
#include <libxml/xmlIO.h>
xmlExternalEntityLoader defaultLoader = NULL;
xmlParserInputPtr
xmlMyExternalEntityLoader(const char *URL, const char *ID,
                               xmlParserCtxtPtr ctxt) {
    xmlParserInputPtr ret;
    const char *fileID = NULL;
    /* lookup for the fileID depending on ID */
    ret = xmlNewInputFromFile(ctxt, fileID);
    if (ret != NULL)
        return(ret);
    if (defaultLoader != NULL)
        ret = defaultLoader(URL, ID, ctxt);
    return(ret);
}
int main(..) {
    ...
    /*
     * Install our own entity loader
     */
    defaultLoader = xmlGetExternalEntityLoader();
    xmlSetExternalEntityLoader(xmlMyExternalEntityLoader);
    ...
}
Example of customized I/O 
This example come from http://xmlsoft.org/messages/0708.htmla
real use case
,  xmlDocDump() closes the FILE * passed by the application
and this was a problem. The 
http://xmlsoft.org/messages/0711.htmlsolution  was to redefine a
new output handler with the closing call deactivated:
  
First define a new I/O output allocator where the output don't close
    the file:
    
xmlOutputBufferPtr
xmlOutputBufferCreateOwn(FILE *file, xmlCharEncodingHandlerPtr encoder) {
    xmlOutputBufferPtr ret;
    
    if (xmlOutputCallbackInitialized == 0)
        xmlRegisterDefaultOutputCallbacks();
    if (file == NULL) return(NULL);
    ret = xmlAllocOutputBuffer(encoder);
    if (ret != NULL) {
        ret->context = file;
        ret->writecallback = xmlFileWrite;
        ret->closecallback = NULL;  /* No close callback */
    }
    return(ret);
} 
  
  
And then use it to save the document:
    
FILE *f;
xmlOutputBufferPtr output;
xmlDocPtr doc;
int res;
f = ...
doc = ....
output = xmlOutputBufferCreateOwn(f, NULL);
res = xmlSaveFileTo(output, doc, NULL);
    
  
Catalog support 
Table of Content:
  
General2General overview   
#definitionThe definition   
#SimpleUsing catalogs   
#SomeSome examples   
#referenceHow to tune  catalog usage   
#validateHow to debug catalog processing   
#DeclaringHow to create and maintain catalogs   
#implementoThe implementor corner quick review of the
  API
  
#OtherOther resources General overview 
What is a catalog? Basically it's a lookup mechanism used when an entity
(a file or a remote resource) references another entity. The catalog lookup
is inserted between the moment the reference is recognized by the software
(XML parser, stylesheet processing, or even images referenced for inclusion
in a rendering) and the time where loading that resource is actually
started.
It is basically used for 3 things:
  
mapping from "logical" names, the public identifiers and a more
    concrete name usable for download (and URI). For example it can associate
    the logical name
    
"-//OASIS//DTD DocBook XML V4.1.2//EN"
    
of the DocBook 4.1.2 XML DTD with the actual URL where it can be
    downloaded
    
http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd
  
  
remapping from a given URL to another one, like an HTTP indirection
    saying that
    
"http://www.oasis-open.org/committes/tr.xsl"
    
should really be looked at
    
"http://www.oasis-open.org/committes/entity/stylesheets/base/tr.xsl"
  
  
providing a local cache mechanism allowing to load the entities
    associated to public identifiers or remote resources, this is a really
    important feature for any significant deployment of XML or SGML since it
    allows to avoid the aleas and delays associated to fetching remote
    resources.
The definitions 
Libxml, as of 2.4.3 implements 2 kind of catalogs:
  
the older SGML catalogs, the official spec is  SGML Open Technical
    Resolution TR9401:1997, but is better understood by reading 
http://www.jclark.com/sp/catalog.htmthe SP Catalog page  from
    James Clark. This is relatively old and not the preferred mode of
    operation of libxml.
  
http://www.oasis-open.org/committees/entity/spec.htmlXML
    Catalogs
 is far more flexible, more recent, uses an XML syntax and
    should scale quite better. This is the default option of libxml.
Using catalog 
In a normal environment libxml2 will by default check the presence of a
catalog in /etc/xml/catalog, and assuming it has been correctly populated,
the processing is completely transparent to the document user. To take a
concrete example, suppose you are authoring a DocBook document, this one
starts with the following DOCTYPE definition:
<?xml version='1.0'?>
<!DOCTYPE book PUBLIC "-//Norman Walsh//DTD DocBk XML V3.1.4//EN"
          "http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd">
When validating the document with libxml, the catalog will be
automatically consulted to lookup the public identifier "-//Norman Walsh//DTD
DocBk XML V3.1.4//EN" and the system identifier
"http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd", and if these entities have
been installed on your system and the catalogs actually point to them, libxml
will fetch them from the local disk.
Note: Really don't use this
DOCTYPE example it's a really old version, but is fine as an example.
Libxml2 will check the catalog each time that it is requested to load an
entity, this includes DTD, external parsed entities, stylesheets, etc ... If
your system is correctly configured all the authoring phase and processing
should use only local files, even if your document stays portable because it
uses the canonical public and system ID, referencing the remote document.
Some examples: 
Here is a couple of fragments from XML Catalogs used in libxml2 early
regression tests in 
test/catalogs :
<?xml version="1.0"?>
<!DOCTYPE catalog PUBLIC 
   "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN"
   "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd">
<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">
  <public publicId="-//OASIS//DTD DocBook XML V4.1.2//EN"
   uri="http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"/>
...
This is the beginning of a catalog for DocBook 4.1.2, XML Catalogs are
written in XML,  there is a specific namespace for catalog elements
"urn:oasis:names:tc:entity:xmlns:xml:catalog". The first entry in this
catalog is a 
public mapping it allows to associate a Public
Identifier with an URI.
...
    <rewriteSystem systemIdStartString="http://www.oasis-open.org/docbook/"
                   rewritePrefix="file:///usr/share/xml/docbook/"/>
...
A rewriteSystem is a very powerful instruction, it says that
any URI starting with a given prefix should be looked at another  URI
constructed by replacing the prefix with an new one. In effect this acts like
a cache system for a full area of the Web. In practice it is extremely useful
with a file prefix if you have installed a copy of those resources on your
local system.
...
<delegatePublic publicIdStartString="-//OASIS//DTD XML Catalog //"
                catalog="file:///usr/share/xml/docbook.xml"/>
<delegatePublic publicIdStartString="-//OASIS//ENTITIES DocBook XML"
                catalog="file:///usr/share/xml/docbook.xml"/>
<delegatePublic publicIdStartString="-//OASIS//DTD DocBook XML"
                catalog="file:///usr/share/xml/docbook.xml"/>
<delegateSystem systemIdStartString="http://www.oasis-open.org/docbook/"
                catalog="file:///usr/share/xml/docbook.xml"/>
<delegateURI uriStartString="http://www.oasis-open.org/docbook/"
                catalog="file:///usr/share/xml/docbook.xml"/>
...
Delegation is the core features which allows to build a tree of catalogs,
easier to maintain than a single catalog, based on Public Identifier, System
Identifier or URI prefixes it instructs the catalog software to look up
entries in another resource. This feature allow to build hierarchies of
catalogs, the set of entries presented should be sufficient to redirect the
resolution of all DocBook references to the specific catalog in
/usr/share/xml/docbook.xml this one in turn could delegate all
references for DocBook 4.2.1 to a specific catalog installed at the same time
as the DocBook resources on the local machine.
How to tune catalog usage: 
The user can change the default catalog behaviour by redirecting queries
to its own set of catalogs, this can be done by setting the
XML_CATALOG_FILES environment variable to a list of catalogs, an
empty one should deactivate loading the default 
/etc/xml/catalogdefault catalog
How to debug catalog processing: 
Setting up the XML_DEBUG_CATALOG environment variable will
make libxml2 output debugging informations for each catalog operations, for
example:
orchis:~/XML -> xmllint --memory --noout test/ent2
warning: failed to load external entity "title.xml"
orchis:~/XML -> export XML_DEBUG_CATALOG=
orchis:~/XML -> xmllint --memory --noout test/ent2
Failed to parse catalog /etc/xml/catalog
Failed to parse catalog /etc/xml/catalog
warning: failed to load external entity "title.xml"
Catalogs cleanup
orchis:~/XML -> 
The test/ent2 references an entity, running the parser from memory makes
the base URI unavailable and the the "title.xml" entity cannot be loaded.
Setting up the debug environment variable allows to detect that an attempt is
made to load the 
/etc/xml/catalog but since it's not present the
resolution fails.
But the most advanced way to debug XML catalog processing is to use the
xmlcatalog command shipped with libxml2, it allows to load
catalogs and make resolution queries to see what is going on. This is also
used for the regression tests:
orchis:~/XML -> ./xmlcatalog test/catalogs/docbook.xml \
                   "-//OASIS//DTD DocBook XML V4.1.2//EN"
http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd
orchis:~/XML -> 
For debugging what is going on, adding one -v flags increase the verbosity
level to indicate the processing done (adding a second flag also indicate
what elements are recognized at parsing):
orchis:~/XML -> ./xmlcatalog -v test/catalogs/docbook.xml \
                   "-//OASIS//DTD DocBook XML V4.1.2//EN"
Parsing catalog test/catalogs/docbook.xml's content
Found public match -//OASIS//DTD DocBook XML V4.1.2//EN
http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd
Catalogs cleanup
orchis:~/XML -> 
A shell interface is also available to debug and process multiple queries
(and for regression tests):
orchis:~/XML -> ./xmlcatalog -shell test/catalogs/docbook.xml \
                   "-//OASIS//DTD DocBook XML V4.1.2//EN"
> help   
Commands available:
public PublicID: make a PUBLIC identifier lookup
system SystemID: make a SYSTEM identifier lookup
resolve PublicID SystemID: do a full resolver lookup
add 'type' 'orig' 'replace' : add an entry
del 'values' : remove values
dump: print the current catalog state
debug: increase the verbosity level
quiet: decrease the verbosity level
exit:  quit the shell
> public "-//OASIS//DTD DocBook XML V4.1.2//EN"
http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd
> quit
orchis:~/XML -> 
This should be sufficient for most debugging purpose, this was actually
used heavily to debug the XML Catalog implementation itself.
How to create and maintain  catalogs:
Basically XML Catalogs are XML files, you can either use XML tools to
manage them or use  
xmlcatalog for this. The basic step is
to create a catalog the -create option provide this facility:
orchis:~/XML -> ./xmlcatalog --create tst.xml
<?xml version="1.0"?>
<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN"
         "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd">
<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"/>
orchis:~/XML -> 
By default xmlcatalog does not overwrite the original catalog and save the
result on the standard output, this can be overridden using the -noout
option. The 
-add command allows to add entries in the
catalog:
orchis:~/XML -> ./xmlcatalog --noout --create --add "public" \
  "-//OASIS//DTD DocBook XML V4.1.2//EN" \
  http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd tst.xml
orchis:~/XML -> cat tst.xml
<?xml version="1.0"?>
<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" \
  "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd">
<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">
<public publicId="-//OASIS//DTD DocBook XML V4.1.2//EN"
        uri="http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"/>
</catalog>
orchis:~/XML -> 
The -add option will always take 3 parameters even if some of
the XML Catalog constructs (like nextCatalog) will have only a single
argument, just pass a third empty string, it will be ignored.
Similarly the -del option remove matching entries from the
catalog:
orchis:~/XML -> ./xmlcatalog --del \
  "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" tst.xml
<?xml version="1.0"?>
<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN"
    "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd">
<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"/>
orchis:~/XML -> 
The catalog is now empty. Note that the matching of -del is
exact and would have worked in a similar fashion with the Public ID
string.
This is rudimentary but should be sufficient to manage a not too complex
catalog tree of resources.
The implementor corner quick review of the
API:
First, and like for every other module of libxml, there is an
automatically generated 
html/libxml-catalog.htmlAPI page for
catalog support
.
The header for the catalog interfaces should be included as:
#include <libxml/catalog.h>The API is voluntarily kept very simple. First it is not obvious that
applications really need access to it since it is the default behaviour of
libxml2 (Note: it is possible to completely override libxml2 default catalog
by using 
html/libxml-parser.htmlxmlSetExternalEntityLoader  to
plug an application specific resolver).
Basically libxml2 support 2 catalog lists:
  
the default one, global shared by all the application  
a per-document catalog, this one is built if the document uses the
    
oasis-xml-catalog PIs to specify its own catalog list, it is
    associated to the parser context and destroyed when the parsing context
    is destroyed.
the document one will be used first if it exists.
Initialization routines:
xmlInitializeCatalog(), xmlLoadCatalog() and xmlLoadCatalogs() should be
used at startup to initialize the catalog, if the catalog should be
initialized with specific values xmlLoadCatalog()  or xmlLoadCatalogs()
should be called before xmlInitializeCatalog() which would otherwise do a
default initialization first.
The xmlCatalogAddLocal() call is used by the parser to grow the document
own catalog list if needed.
Preferences setup:
The XML Catalog spec requires the possibility to select default
preferences between  public and system delegation,
xmlCatalogSetDefaultPrefer() allows this, xmlCatalogSetDefaults() and
xmlCatalogGetDefaults() allow to control  if XML Catalogs resolution should
be forbidden, allowed for global catalog, for document catalog or both, the
default is to allow both.
And of course xmlCatalogSetDebug() allows to generate debug messages
(through the xmlGenericError() mechanism).
Querying routines:
xmlCatalogResolve(), xmlCatalogResolveSystem(), xmlCatalogResolvePublic()
and xmlCatalogResolveURI() are relatively explicit if you read the XML
Catalog specification they correspond to section 7 algorithms, they should
also work if you have loaded an SGML catalog with a simplified semantic.
xmlCatalogLocalResolve() and xmlCatalogLocalResolveURI() are the same but
operate on the document catalog list
Cleanup and Miscellaneous:
xmlCatalogCleanup() free-up the global catalog, xmlCatalogFreeLocal() is
the per-document equivalent.
xmlCatalogAdd() and xmlCatalogRemove() are used to dynamically modify the
first catalog in the global list, and xmlCatalogDump() allows to dump a
catalog state, those routines are primarily designed for xmlcatalog, I'm not
sure that exposing more complex interfaces (like navigation ones) would be
really useful.
The xmlParseCatalogFile() is a function used to load XML Catalog files,
it's similar as xmlParseFile() except it bypass all catalog lookups, it's
provided because this functionality may be useful for client tools.
threaded environments:
Since the catalog tree is built progressively, some care has been taken to
try to avoid troubles in multithreaded environments. The code is now thread
safe assuming that the libxml2 library has been compiled with threads
support.
Other resources 
The XML Catalog specification is relatively recent so there isn't much
literature to point at:
  
You can find a good rant from Norm Walsh about http://www.arbortext.com/Think_Tank/XML_Resources/Issue_Three/issue_three.htmlthe
    need for catalogs
, it provides a lot of context informations even if
    I don't agree with everything presented. Norm also wrote a more recent
    article 
http://wwws.sun.com/software/xml/developers/resolver/article/XML
    entities and URI resolvers
 describing them.  
An http://home.ccil.org/~cowan/XML/XCatalog.htmlold XML
    catalog proposal
 from John Cowan  
The http://www.rddl.org/Resource Directory Description
    Language
 (RDDL) another catalog system but more oriented toward
    providing metadata for XML namespaces.
  
the page from the OASIS Technical http://www.oasis-open.org/committees/entity/Committee on Entity
    Resolution
 who maintains XML Catalog, you will find pointers to the
    specification update, some background and pointers to others tools
    providing XML Catalog support
  
There is a buildDocBookCatalogshell script  to generate
    XML Catalogs for DocBook 4.1.2 . If it can write to the /etc/xml/
    directory, it will set-up /etc/xml/catalog and /etc/xml/docbook based on
    the resources found on the system. Otherwise it will just create
    ~/xmlcatalog and ~/dbkxmlcatalog and doing:
    
export XML_CATALOG_FILES=$HOME/xmlcatalog
    
should allow to process DocBook documentations without requiring
    network accesses for the DTD or stylesheets
  
  
I have uploaded ftp://xmlsoft.org/test/dbk412catalog.tar.gza
    small tarball
 containing XML Catalogs for DocBook 4.1.2 which seems
    to work fine for me too
  
The http://www.xmlsoft.org/xmlcatalog_man.htmlxmlcatalog
    manual page
If you have suggestions for corrections or additions, simply contact
me:
The parser interfaces 
This section is directly intended to help programmers getting bootstrapped
using the XML tollkit from the C language. It is not intended to be
extensive. I hope the automatically generated documents will provide the
completeness required, but as a separate set of documents. The interfaces of
the XML parser are by principle low level, Those interested in a higher level
API should 
#DOMlook at DOM .
The html/libxml-parser.htmlparser interfaces for XML  are
separated from the 
html/libxml-htmlparser.htmlHTML parser
interfaces
.  Let's have a look at how the XML parser can be called:
Invoking the parser : the pull method 
Usually, the first thing to do is to read an XML input. The parser accepts
documents either from in-memory strings or from files.  The functions are
defined in "parser.h":
  
xmlDocPtr xmlParseMemory(char *buffer, int size);    
Parse a null-terminated string containing the document.
    
  
xmlDocPtr xmlParseFile(const char *filename);    
Parse an XML document contained in a (possibly compressed)
      file.
    
The parser returns a pointer to the document structure (or NULL in case of
failure).
Invoking the parser: the push method
In order for the application to keep the control when the document is
being fetched (which is common for GUI based programs) libxml2 provides a
push interface, too, as of version 1.8.3. Here are the interface
functions:
xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax,
                                         void *user_data,
                                         const char *chunk,
                                         int size,
                                         const char *filename);
int              xmlParseChunk          (xmlParserCtxtPtr ctxt,
                                         const char *chunk,
                                         int size,
                                         int terminate);
and here is a simple example showing how to use the interface:
            FILE *f;
            f = fopen(filename, "r");
            if (f != NULL) {
                int res, size = 1024;
                char chars[1024];
                xmlParserCtxtPtr ctxt;
                res = fread(chars, 1, 4, f);
                if (res > 0) {
                    ctxt = xmlCreatePushParserCtxt(NULL, NULL,
                                chars, res, filename);
                    while ((res = fread(chars, 1, size, f)) > 0) {
                        xmlParseChunk(ctxt, chars, res, 0);
                    }
                    xmlParseChunk(ctxt, chars, 0, 1);
                    doc = ctxt->myDoc;
                    xmlFreeParserCtxt(ctxt);
                }
            }
The HTML parser embedded into libxml2 also has a push interface; the
functions are just prefixed by "html" rather than "xml".
Invoking the parser: the SAX interface
The tree-building interface makes the parser memory-hungry, first loading
the document in memory and then building the tree itself. Reading a document
without building the tree is possible using the SAX interfaces (see SAX.h and
http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.htmlJames
Henstridge's documentation
). Note also that the push interface can be
limited to SAX: just use the two first arguments of
xmlCreatePushParserCtxt().
Building a tree from scratch 
The other way to get an XML tree in memory is by building it. Basically
there is a set of functions dedicated to building new elements. (These are
also described in <libxml/tree.h>.) For example, here is a piece of
code that produces the XML document used in the previous examples:
    #include <libxml/tree.h>
    xmlDocPtr doc;
    xmlNodePtr tree, subtree;
    doc = xmlNewDoc("1.0");
    doc->children = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL);
    xmlSetProp(doc->children, "prop1", "gnome is great");
    xmlSetProp(doc->children, "prop2", "& linux too");
    tree = xmlNewChild(doc->children, NULL, "head", NULL);
    subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome");
    tree = xmlNewChild(doc->children, NULL, "chapter", NULL);
    subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure");
    subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ...");
    subtree = xmlNewChild(tree, NULL, "image", NULL);
    xmlSetProp(subtree, "href", "linus.gif");
Not really rocket science ...
Traversing the tree 
Basically by html/libxml-tree.htmlincluding "tree.h"  your
code has access to the internal structure of all the elements of the tree.
The names should be somewhat simple like 
parent,
children, next, prev,
properties, etc... For example, still with the previous
example:
doc->children->children->childrenpoints to the title element,
doc->children->children->next->children->childrenpoints to the text node containing the chapter title "The Linux
adventure".
NOTE: XML allows PIs and comments to be
present before the document root, so 
doc->children may point
to an element which is not the document Root Element; a function
xmlDocGetRootElement() was added for this purpose.
Modifying the tree 
Functions are provided for reading and writing the document content. Here
is an excerpt from the 
html/libxml-tree.htmltree API :
  
xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
  xmlChar *value);
    
This sets (or changes) an attribute carried by an ELEMENT node.
      The value can be NULL.
    
  
const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
  *name);
    
This function returns a pointer to new copy of the property
      content. Note that the user must deallocate the result.
    
Two functions are provided for reading and writing the text associated
with elements:
  
xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
  *value);
    
This function takes an "external" string and converts it to one
      text node or possibly to a list of entity and text nodes. All
      non-predefined entity references like &Gnome; will be stored
      internally as entity nodes, hence the result of the function may not be
      a single node.
    
  
xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
  inLine);
    
This function is the inverse of
      
xmlStringGetNodeList(). It generates a new string
      containing the content of the text and entity nodes. Note the extra
      argument inLine. If this argument is set to 1, the function will expand
      entity references.  For example, instead of returning the &Gnome;
      XML encoding in the string, it will substitute it with its value (say,
      "GNU Network Object Model Environment").
    
Saving a tree 
Basically 3 options are possible:
  
void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
  *size);
    
Returns a buffer into which the document has been saved.
    
  
extern void xmlDocDump(FILE *f, xmlDocPtr doc);    
Dumps a document to an open file descriptor.
    
  
int xmlSaveFile(const char *filename, xmlDocPtr cur);    
Saves the document to a file. In this case, the compression
      interface is triggered if it has been turned on.
    
Compression 
The library transparently handles compression when doing file-based
accesses. The level of compression on saves can be turned on either globally
or individually for one file:
  
int  xmlGetDocCompressMode (xmlDocPtr doc);    
Gets the document compression ratio (0-9).
    
  
void xmlSetDocCompressMode (xmlDocPtr doc, int mode);    
Sets the document compression ratio.
    
  
int  xmlGetCompressMode(void);    
Gets the default compression ratio.
    
  
void xmlSetCompressMode(int mode);    
Sets the default compression ratio.
    
Entities or no entities 
Entities in principle are similar to simple C macros. An entity defines an
abbreviation for a given string that you can reuse many times throughout the
content of your document. Entities are especially useful when a given string
may occur frequently within a document, or to confine the change needed to a
document to a restricted area in the internal subset of the document (at the
beginning). Example:
1 <?xml version="1.0"?>
2 <!DOCTYPE EXAMPLE SYSTEM "example.dtd" [
3 <!ENTITY xml "Extensible Markup Language">
4 ]>
5 <EXAMPLE>
6    &xml;
7 </EXAMPLE>
Line 3 declares the xml entity. Line 6 uses the xml entity, by prefixing
its name with '&' and following it by ';' without any spaces added. There
are 5 predefined entities in libxml2 allowing you to escape characters with
predefined meaning in some parts of the xml document content:
&lt; for the character '<', &gt;for the character '>',  
&apos; for the character ''',
&quot; for the character '"', and
&amp; for the character '&'.
One of the problems related to entities is that you may want the parser to
substitute an entity's content so that you can see the replacement text in
your application. Or you may prefer to keep entity references as such in the
content to be able to save the document back without losing this usually
precious information (if the user went through the pain of explicitly
defining entities, he may have a a rather negative attitude if you blindly
substitute them as saving time). The 
html/libxml-parser.html#xmlSubstituteEntitiesDefaultxmlSubstituteEntitiesDefault() function allows you to check and change the behaviour, which is to not
substitute entities by default.
Here is the DOM tree built by libxml2 for the previous document in the
default case:
/gnome/src/gnome-xml -> ./xmllint --debug test/ent1
DOCUMENT
version=1.0
   ELEMENT EXAMPLE
     TEXT
     content=
     ENTITY_REF
       INTERNAL_GENERAL_ENTITY xml
       content=Extensible Markup Language
     TEXT
     content=
And here is the result when substituting entities:
/gnome/src/gnome-xml -> ./tester --debug --noent test/ent1
DOCUMENT
version=1.0
   ELEMENT EXAMPLE
     TEXT
     content=     Extensible Markup Language
So, entities or no entities? Basically, it depends on your use case. I
suggest that you keep the non-substituting default behaviour and avoid using
entities in your XML document or data if you are not willing to handle the
entity references elements in the DOM tree.
Note that at save time libxml2 enforces the conversion of the predefined
entities where necessary to prevent well-formedness problems, and will also
transparently replace those with chars (i.e. it will not generate entity
reference elements in the DOM tree or call the reference() SAX callback when
finding them in the input).
WARNING: handling entities
on top of the libxml2 SAX interface is difficult!!! If you plan to use
non-predefined entities in your documents, then the learning curve to handle
then using the SAX API may be long. If you plan to use complex documents, I
strongly suggest you consider using the DOM interface instead and let libxml
deal with the complexity rather than trying to do it yourself.
Namespaces 
The libxml2 library implements http://www.w3.org/TR/REC-xml-names/XML namespaces  support by
recognizing namespace constructs in the input, and does namespace lookup
automatically when building the DOM tree. A namespace declaration is
associated with an in-memory structure and all elements or attributes within
that namespace point to it. Hence testing the namespace is a simple and fast
equality operation at the user level.
I suggest that people using libxml2 use a namespace, and declare it in the
root element of their document as the default namespace. Then they don't need
to use the prefix in the content but we will have a basis for future semantic
refinement and  merging of data from different sources. This doesn't increase
the size of the XML output significantly, but significantly increases its
value in the long-term. Example:
<mydoc xmlns="http://mydoc.example.org/schemas/">
   <elem1>...</elem1>
   <elem2>...</elem2>
</mydoc>
The namespace value has to be an absolute URL, but the URL doesn't have to
point to any existing resource on the Web. It will bind all the element and
attributes with that URL. I suggest to use an URL within a domain you
control, and that the URL should contain some kind of version information if
possible. For example, 
"http://www.gnome.org/gnumeric/1.0/" is a
good namespace scheme.
Then when you load a file, make sure that a namespace carrying the
version-independent prefix is installed on the root element of your document,
and if the version information don't match something you know, warn the user
and be liberal in what you accept as the input. Also do *not* try to base
namespace checking on the prefix value. <foo:text> may be exactly the
same as <bar:text> in another document. What really matters is the URI
associated with the element or the attribute, not the prefix string (which is
just a shortcut for the full URI). In libxml, element and attributes have an
ns field pointing to an xmlNs structure detailing the namespace
prefix and its URI.
@@Interfaces@@
xmlNodePtr node;
if(!strncmp(node->name,"mytag",5)
  && node->ns
  && !strcmp(node->ns->href,"http://www.mysite.com/myns/1.0")) {
  ...
}
Usually people object to using namespaces together with validity checking.
I will try to make sure that using namespaces won't break validity checking,
so even if you plan to use or currently are using validation I strongly
suggest adding namespaces to your document. A default namespace scheme
xmlns="http://...." should not break validity even on less
flexible parsers. Using namespaces to mix and differentiate content coming
from multiple DTDs will certainly break current validation schemes. To check
such documents one needs to use schema-validation, which is supported in
libxml2 as well. See 
http://www.relaxng.org/relagx-ng  and http://www.w3c.org/XML/Schemaw3c-schema .
Upgrading 1.x code 
Incompatible changes:
Version 2 of libxml2 is the first version introducing serious backward
incompatible changes. The main goals were:
  
a general cleanup. A number of mistakes inherited from the very early
    versions couldn't be changed due to compatibility constraints. Example
    the "childs" element in the nodes.
  
Uniformization of the various nodes, at least for their header and link
    parts (doc, parent, children, prev, next), the goal is a simpler
    programming model and simplifying the task of the DOM implementors.
  
better conformances to the XML specification, for example version 1.x
    had an heuristic to try to detect ignorable white spaces. As a result the
    SAX event generated were ignorableWhitespace() while the spec requires
    character() in that case. This also mean that a number of DOM node
    containing blank text may populate the DOM tree which were not present
    before.
How to fix libxml-1.x code:
So client code of libxml designed to run with version 1.x may have to be
changed to compile against version 2.x of libxml. Here is a list of changes
that I have collected, they may not be sufficient, so in case you find other
change which are required, 
mailto:Daniel.Veillard@w3.orgdrop me a
mail
:
  
The package name have changed from libxml to libxml2, the library name
    is now -lxml2 . There is a new xml2-config script which should be used to
    select the right parameters libxml2
  
Node childs field has been renamed
    
children so s/childs/children/g should be  applied
    (probability of having "childs" anywhere else is close to 0+
  
The document don't have anymore a root element it has
    been replaced by 
children and usually you will get a
    list of element here. For example a Dtd element for the internal subset
    and it's declaration may be found in that list, as well as processing
    instructions or comments found before or after the document root element.
    Use 
xmlDocGetRootElement(doc) to get the root element of
    a document. Alternatively if you are sure to not reference DTDs nor have
    PIs or comments before or after the root element
    s/->root/->children/g will probably do it.
  
The white space issue, this one is more complex, unless special case of
    validating parsing, the line breaks and spaces usually used for indenting
    and formatting the document content becomes significant. So they are
    reported by SAX and if your using the DOM tree, corresponding nodes are
    generated. Too approach can be taken:
    
      
lazy one, use the compatibility call
        
xmlKeepBlanksDefault(0) but be aware that you are
        relying on a special (and possibly broken) set of heuristics of
        libxml to detect ignorable blanks. Don't complain if it breaks or
        make your application not 100% clean w.r.t. to it's input.
      
the Right Way: change you code to accept possibly insignificant
        blanks characters, or have your tree populated with weird blank text
        nodes. You can spot them using the commodity function
        
xmlIsBlankNode(node) returning 1 for such blank
        nodes.
    
    
Note also that with the new default the output functions don't add any
    extra indentation when saving a tree in order to be able to round trip
    (read and save) without inflating the document with extra formatting
    chars.
  
  
The include path has changed to $prefix/libxml/ and the includes
    themselves uses this new prefix in includes instructions... If you are
    using (as expected) the
    
xml2-config --cflags    
output to generate you compile commands this will probably work out of
    the box
  
  
xmlDetectCharEncoding takes an extra argument indicating the length in
    byte of the head of the document available for character detection.
Ensuring both libxml-1.x and libxml-2.x compatibility
Two new version of libxml (1.8.11) and libxml2 (2.3.4) have been released
to allow smooth upgrade of existing libxml v1code while retaining
compatibility. They offers the following:
  
similar include naming, one should use
    
#include<libxml/...> in both cases.  
similar identifiers defined via macros for the child and root fields:
    respectively 
xmlChildrenNode and
    
xmlRootNode  
a new macro LIBXML_TEST_VERSION which should be
    inserted once in the client code
So the roadmap to upgrade your existing libxml applications is the
following:
  
install the  libxml-1.8.8 (and libxml-devel-1.8.8) packages  
find all occurrences where the xmlDoc root field is
    used and change it to 
xmlRootNode  
similarly find all occurrences where the xmlNode
    
childs field is used and change it to
    
xmlChildrenNode  
add a LIBXML_TEST_VERSION macro somewhere in your
    
main() or in the library init entry point  
Recompile, check compatibility, it should still work  
Change your configure script to look first for xml2-config and fall
    back using xml-config . Use the --cflags and --libs output of the command
    as the Include and Linking parameters needed to use libxml.
  
install libxml2-2.3.x and  libxml2-devel-2.3.x (libxml-1.8.y and
    libxml-devel-1.8.y can be kept simultaneously)
  
remove your config.cache, relaunch your configuration mechanism, and
    recompile, if steps 2 and 3 were done right it should compile as-is
  
Test that your application is still running correctly, if not this may
    be due to extra empty nodes due to formating spaces being kept in libxml2
    contrary to libxml1, in that case insert xmlKeepBlanksDefault(1) in your
    code before calling the parser (next to
    
LIBXML_TEST_VERSION is a fine place).Following those steps should work. It worked for some of my own code.
Let me put some emphasis on the fact that there is far more changes from
libxml 1.x to 2.x than the ones you may have to patch for. The overall code
has been considerably cleaned up and the conformance to the XML specification
has been drastically improved too. Don't take those changes as an excuse to
not upgrade, it may cost a lot on the long term ...
Thread safety 
Starting with 2.4.7, libxml2 makes provisions to ensure that concurrent
threads can safely work in parallel parsing different documents. There is
however a couple of things to do to ensure it:
  
configure the library accordingly using the --with-threads options  
call xmlInitParser() in the "main" thread before using any of the
    libxml2 API (except possibly selecting a different memory allocator)
Note that the thread safety cannot be ensured for multiple threads sharing
the same document, the locking must be done at the application level, libxml
exports a basic mutex and reentrant mutexes API in <libxml/threads.h>.
The parts of the library checked for thread safety are:
  
concurrent loading  
file access resolution  
catalog access  
catalog building  
entities lookup/accesses  
validation  
global variables per-thread override  
memory handlingXPath is supposed to be thread safe now, but this wasn't tested
seriously.
DOM Principles 
http://www.w3.org/DOM/DOM  stands for the Document
Object Model
; this is an API for accessing XML or HTML structured
documents. Native support for DOM in Gnome is on the way (module gnome-dom),
and will be based on gnome-xml. This will be a far cleaner interface to
manipulate XML files within Gnome since it won't expose the internal
structure.
The current DOM implementation on top of libxml2 is the http://cvs.gnome.org/lxr/source/gdome2/gdome2 Gnome module , this
is a full DOM interface, thanks to Paolo Casarini, check the 
http://www.cs.unibo.it/~casarini/gdome2/Gdome2 homepage  for more
informations.
A real example 
Here is a real size example, where the actual content of the application
data is not kept in the DOM tree but uses internal structures. It is based on
a proposal to keep a database of jobs related to Gnome, with an XML based
storage structure. Here is an 
gjobs.xmlXML encoded jobs
base
:
<?xml version="1.0"?>
<gjob:Helping xmlns:gjob="http://www.gnome.org/some-location">
  <gjob:Jobs>
    <gjob:Job>
      <gjob:Project ID="3"/>
      <gjob:Application>GBackup</gjob:Application>
      <gjob:Category>Development</gjob:Category>
      <gjob:Update>
        <gjob:Status>Open</gjob:Status>
        <gjob:Modified>Mon, 07 Jun 1999 20:27:45 -0400 MET DST</gjob:Modified>
        <gjob:Salary>USD 0.00</gjob:Salary>
      </gjob:Update>
      <gjob:Developers>
        <gjob:Developer>
        </gjob:Developer>
      </gjob:Developers>
      <gjob:Contact>
        <gjob:Person>Nathan Clemons</gjob:Person>
        <gjob:Email>nathan@windsofstorm.net</gjob:Email>
        <gjob:Company>
        </gjob:Company>
        <gjob:Organisation>
        </gjob:Organisation>
        <gjob:Webpage>
        </gjob:Webpage>
        <gjob:Snailmail>
        </gjob:Snailmail>
        <gjob:Phone>
        </gjob:Phone>
      </gjob:Contact>
      <gjob:Requirements>
      The program should be released as free software, under the GPL.
      </gjob:Requirements>
      <gjob:Skills>
      </gjob:Skills>
      <gjob:Details>
      A GNOME based system that will allow a superuser to configure 
      compressed and uncompressed files and/or file systems to be backed 
      up with a supported media in the system.  This should be able to 
      perform via find commands generating a list of files that are passed 
      to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine 
      or via operations performed on the filesystem itself. Email 
      notification and GUI status display very important.
      </gjob:Details>
    </gjob:Job>
  </gjob:Jobs>
</gjob:Helping>
While loading the XML file into an internal DOM tree is a matter of
calling only a couple of functions, browsing the tree to gather the data and
generate the internal structures is harder, and more error prone.
The suggested principle is to be tolerant with respect to the input
structure. For example, the ordering of the attributes is not significant,
the XML specification is clear about it. It's also usually a good idea not to
depend on the order of the children of a given node, unless it really makes
things harder. Here is some code to parse the information for a person:
/*
 * A person record
 */
typedef struct person {
    char *name;
    char *email;
    char *company;
    char *organisation;
    char *smail;
    char *webPage;
    char *phone;
} person, *personPtr;
/*
 * And the code needed to parse it
 */
personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
    personPtr ret = NULL;
DEBUG("parsePerson\n");
    /*
     * allocate the struct
     */
    ret = (personPtr) malloc(sizeof(person));
    if (ret == NULL) {
        fprintf(stderr,"out of memory\n");
        return(NULL);
    }
    memset(ret, 0, sizeof(person));
    /* We don't care what the top level element name is */
    cur = cur->xmlChildrenNode;
    while (cur != NULL) {
        if ((!strcmp(cur->name, "Person")) && (cur->ns == ns))
            ret->name = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
        if ((!strcmp(cur->name, "Email")) && (cur->ns == ns))
            ret->email = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
        cur = cur->next;
    }
    return(ret);
}
Here are a couple of things to notice:
  
Usually a recursive parsing style is the more convenient one: XML data
    is by nature subject to repetitive constructs and usually exhibits highly
    structured patterns.
  
The two arguments of type xmlDocPtr and xmlNsPtr,
    i.e. the pointer to the global XML document and the namespace reserved to
    the application. Document wide information are needed for example to
    decode entities and it's a good coding practice to define a namespace for
    your application set of data and test that the element and attributes
    you're analyzing actually pertains to your application space. This is
    done by a simple equality test (cur->ns == ns).
  
To retrieve text and attributes value, you can use the function
    
xmlNodeListGetString to gather all the text and entity reference
    nodes generated by the DOM output and produce an single text string.
Here is another piece of code used to parse another level of the
structure:
#include <libxml/tree.h>
/*
 * a Description for a Job
 */
typedef struct job {
    char *projectID;
    char *application;
    char *category;
    personPtr contact;
    int nbDevelopers;
    personPtr developers[100]; /* using dynamic alloc is left as an exercise */
} job, *jobPtr;
/*
 * And the code needed to parse it
 */
jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
    jobPtr ret = NULL;
DEBUG("parseJob\n");
    /*
     * allocate the struct
     */
    ret = (jobPtr) malloc(sizeof(job));
    if (ret == NULL) {
        fprintf(stderr,"out of memory\n");
        return(NULL);
    }
    memset(ret, 0, sizeof(job));
    /* We don't care what the top level element name is */
    cur = cur->xmlChildrenNode;
    while (cur != NULL) {
        
        if ((!strcmp(cur->name, "Project")) && (cur->ns == ns)) {
            ret->projectID = xmlGetProp(cur, "ID");
            if (ret->projectID == NULL) {
                fprintf(stderr, "Project has no ID\n");
            }
        }
        if ((!strcmp(cur->name, "Application")) && (cur->ns == ns))
            ret->application = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
        if ((!strcmp(cur->name, "Category")) && (cur->ns == ns))
            ret->category = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);
        if ((!strcmp(cur->name, "Contact")) && (cur->ns == ns))
            ret->contact = parsePerson(doc, ns, cur);
        cur = cur->next;
    }
    return(ret);
}
Once you are used to it, writing this kind of code is quite simple, but
boring. Ultimately, it could be possible to write stubbers taking either C
data structure definitions, a set of XML examples or an XML DTD and produce
the code needed to import and export the content between C data and XML
storage. This is left as an exercise to the reader :-)
Feel free to use example/gjobread.cthe code for the full C
parsing example
 as a template, it is also available with Makefile in the
Gnome CVS base under gnome-xml/example
Contributions 
  
Bjorn Reese, William Brack and Thomas Broyer have provided a number of
    patches, Gary Pennington worked on the validation API, threading support
    and Solaris port.
  
John Fleck helps maintaining the documentation and man pages.  
mailto:igor@zlatkovic.comIgor  Zlatkovic  is now the
    maintainer of the Windows port, 
http://www.zlatkovic.com/projects/libxml/index.htmlhe provides
    binaries
  
mailto:Gary.Pennington@sun.comGary Pennington  provides
    
http://garypennington.net/libxml2/Solaris binaries   
http://mail.gnome.org/archives/xml/2001-March/msg00014.htmlMatt
    Sergeant
 developed http://axkit.org/download/XML::LibXSLT , a Perl wrapper for
    libxml2/libxslt as part of the 
http://axkit.com/AxKit XML
    application server
  
mailto:fnatter@gmx.netFelix Natter  and mailto:geertk@ai.rug.nlGeert Kloosterman  provide libxml-doc.elan emacs module  to lookup libxml(2) functions
    documentation
  
mailto:sherwin@nlm.nih.govZiying Sherwin  provided http://xmlsoft.org/messages/0488.htmlman pages   
there is a module for http://acs-misc.sourceforge.net/nsxml.htmllibxml/libxslt support
    in OpenNSD/AOLServer
  
mailto:dkuhlman@cutter.rexx.comDave Kuhlman  provided the
    first version of libxml/libxslt 
http://www.rexx.com/~dkuhlmanwrappers for Python   
Petr Kozelka provides http://sourceforge.net/projects/libxml2-pasPascal units to glue
    libxml2
 with Kylix and Delphi and other Pascal compilers  
mailto:aleksey@aleksey.comAleksey Sanin  implemented the
    
http://www.w3.org/Signature/XML Canonicalization and XML
    Digital Signature
 http://www.aleksey.com/xmlsec/implementations for libxml2   
mailto:Steve.Ball@explain.com.auSteve Ball  and
    contributors maintain 
http://tclxml.sourceforge.net/tcl
    bindings for libxml2 and libxslt
, as well as http://tclxml.sf.net/tkxmllint.htmltkxmllint  a GUI for
    xmllint and 
http://tclxml.sf.net/tkxsltproc.htmltkxsltproc     a GUI for xsltproc.
