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LibXML.pod

=head1 NAME

XML::LibXML - Perl Binding for libxml2

=head1 SYNOPSIS

use XML::LibXML;
  my $dom = XML::LibXML->load_xml(string => <<'EOT');
  <some-xml/>
  EOT

$Version_String = XML::LibXML::LIBXML_DOTTED_VERSION;
  $Version_ID = XML::LibXML::LIBXML_VERSION;
  $DLL_Version = XML::LibXML::LIBXML_RUNTIME_VERSION;
  $libxmlnode = XML::LibXML->import_GDOME( $node, $deep );
  $gdomenode = XML::LibXML->export_GDOME( $node, $deep );

=head1 DESCRIPTION

This module is an interface to libxml2, providing XML and HTML parsers with
DOM, SAX and XMLReader interfaces, a large subset of DOM Layer 3 interface and
a XML::XPath-like interface to XPath API of libxml2. The module is split into
several packages which are not described in this section; unless stated
otherwise, you only need to C<<<<<< use XML::LibXML; >>>>>> in your programs.

Check out XML::LibXML by Example (L<<<<<< http://grantm.github.io/perl-libxml-by-example/ >>>>>>) for a tutorial.

For further information, please check the following documentation:

=over 4

=item L<<<<<< XML::LibXML::Parser >>>>>>

Parsing XML files with XML::LibXML

=item L<<<<<< XML::LibXML::DOM >>>>>>

XML::LibXML Document Object Model (DOM) Implementation

=item L<<<<<< XML::LibXML::SAX >>>>>>

XML::LibXML direct SAX parser

=item L<<<<<< XML::LibXML::Reader >>>>>>

Reading XML with a pull-parser

=item L<<<<<< XML::LibXML::Dtd >>>>>>

XML::LibXML frontend for DTD validation

=item L<<<<<< XML::LibXML::RelaxNG >>>>>>

XML::LibXML frontend for RelaxNG schema validation

=item L<<<<<< XML::LibXML::Schema >>>>>>

XML::LibXML frontend for W3C Schema schema validation

=item L<<<<<< XML::LibXML::XPathContext >>>>>>

API for evaluating XPath expressions with enhanced support for the evaluation
context

=item L<<<<<< XML::LibXML::InputCallback >>>>>>

Implementing custom URI Resolver and input callbacks

=item L<<<<<< XML::LibXML::Common >>>>>>

Common functions for XML::LibXML related Classes

=back

The nodes in the Document Object Model (DOM) are represented by the following
classes (most of which "inherit" from L<<<<<< XML::LibXML::Node >>>>>>):

=over 4

=item L<<<<<< XML::LibXML::Document >>>>>>

XML::LibXML class for DOM document nodes

=item L<<<<<< XML::LibXML::Node >>>>>>

Abstract base class for XML::LibXML DOM nodes

=item L<<<<<< XML::LibXML::Element >>>>>>

XML::LibXML class for DOM element nodes

=item L<<<<<< XML::LibXML::Text >>>>>>

XML::LibXML class for DOM text nodes

=item L<<<<<< XML::LibXML::Comment >>>>>>

XML::LibXML class for comment DOM nodes

=item L<<<<<< XML::LibXML::CDATASection >>>>>>

XML::LibXML class for DOM CDATA sections

=item L<<<<<< XML::LibXML::Attr >>>>>>

XML::LibXML DOM attribute class

=item L<<<<<< XML::LibXML::DocumentFragment >>>>>>

XML::LibXML's DOM L2 Document Fragment implementation

=item L<<<<<< XML::LibXML::Namespace >>>>>>

XML::LibXML DOM namespace nodes

=item L<<<<<< XML::LibXML::PI >>>>>>

XML::LibXML DOM processing instruction nodes

=back

=head1 ENCODINGS SUPPORT IN XML::LIBXML

Recall that since version 5.6.1, Perl distinguishes between character strings
(internally encoded in UTF-8) and so called binary data and, accordingly,
applies either character or byte semantics to them. A scalar representing a
character string is distinguished from a byte string by special flag (UTF8).
Please refer to I<<<<<< perlunicode >>>>>> for details.

XML::LibXML's API is designed to deal with many encodings of XML documents
completely transparently, so that the application using XML::LibXML can be
completely ignorant about the encoding of the XML documents it works with. On
the other hand, functions like C<<<<<< XML::LibXML::Document-E<gt>setEncoding >>>>>> give the user control over the document encoding.

To ensure the aforementioned transparency and uniformity, most functions of
XML::LibXML that work with in-memory trees accept and return data as character
strings (i.e. UTF-8 encoded with the UTF8 flag on) regardless of the original
document encoding; however, the functions related to I/O operations (i.e.
parsing and saving) operate with binary data (in the original document
encoding) obeying the encoding declaration of the XML documents.

Below we summarize basic rules and principles regarding encoding:

=over 4

=item 1.

Do NOT apply any encoding-related PerlIO layers (C<<<<<< :utf8 >>>>>> or C<<<<<< :encoding(...) >>>>>>) to file handles that are an input for the parses or an output for a
serializer of (full) XML documents. This is because the conversion of the data
to/from the internal character representation is provided by libxml2 itself
which must be able to enforce the encoding specified by the C<<<<<< E<lt>?xml version="1.0" encoding="..."?E<gt> >>>>>> declaration. Here is an example to follow:

use XML::LibXML;
  # load
  open my $fh, '<', 'file.xml';
  binmode $fh; # drop all PerlIO layers possibly created by a use open pragma
  $doc = XML::LibXML->load_xml(IO => $fh);

# save
  open my $out, '>', 'out.xml';
  binmode $out; # as above
  $doc->toFH($out);
  # or
  print {$out} $doc->toString();

=item 2.

All functions working with DOM accept and return character strings (UTF-8
encoded with UTF8 flag on). E.g.

my $doc = XML::LibXML::Document->new('1.0',$some_encoding);
  my $element = $doc->createElement($name);
  $element->appendText($text);
  $xml_fragment = $element->toString(); # returns a character string
  $xml_document = $doc->toString(); # returns a byte string

where C<<<<<< $some_encoding >>>>>> is the document encoding that will be used when saving the document, and C<<<<<< $name >>>>>> and C<<<<<< $text >>>>>> contain character strings (UTF-8 encoded with UTF8 flag on). Note that the
method C<<<<<< toString >>>>>> returns XML as a character string if applied to other node than the Document
node and a byte string containing the appropriate

<?xml version="1.0" encoding="..."?>

declaration if applied to a L<<<<<< XML::LibXML::Document >>>>>>.

=item 3.

DOM methods also accept binary strings in the original encoding of the document
to which the node belongs (UTF-8 is assumed if the node is not attached to any
document). Exploiting this feature is NOT RECOMMENDED since it is considered
bad practice.

my $doc = XML::LibXML::Document->new('1.0','iso-8859-2');
  my $text = $doc->createTextNode($some_latin2_encoded_byte_string);
  # WORKS, BUT NOT RECOMMENDED!

=back

I<<<<<< NOTE: >>>>>> libxml2 support for many encodings is based on the iconv library. The actual
list of supported encodings may vary from platform to platform. To test if your
platform works correctly with your language encoding, build a simple document
in the particular encoding and try to parse it with XML::LibXML to see if the
parser produces any errors. Occasional crashes were reported on rare platforms
that ship with a broken version of iconv.

=head1 THREAD SUPPORT

XML::LibXML since 1.67 partially supports Perl threads in Perl >= 5.8.8.
XML::LibXML can be used with threads in two ways:

By default, all XML::LibXML classes use CLONE_SKIP class method to prevent Perl
from copying XML::LibXML::* objects when a new thread is spawn. In this mode,
all XML::LibXML::* objects are thread specific. This is the safest way to work
with XML::LibXML in threads.

Alternatively, one may use

use threads;
  use XML::LibXML qw(:threads_shared);

to indicate, that all XML::LibXML node and parser objects should be shared
between the main thread and any thread spawn from there. For example, in

my $doc = XML::LibXML->load_xml(location => $filename);
  my $thr = threads->new(sub{
    # code working with $doc
    1;
  });
  $thr->join;

the variable C<<<<<< $doc >>>>>> refers to the exact same XML::LibXML::Document in the spawned thread as in the
main thread.

Without using mutex locks, parallel threads may read the same document (i.e.
any node that belongs to the document), parse files, and modify different
documents.

However, if there is a chance that some of the threads will attempt to modify a
document (or even create new nodes based on that document, e.g. with C<<<<<< $doc-E<gt>createElement >>>>>>) that other threads may be reading at the same time, the user is responsible
for creating a mutex lock and using it in I<<<<<< both >>>>>> in the thread that modifies and the thread that reads:

my $doc = XML::LibXML->load_xml(location => $filename);
  my $mutex : shared;
  my $thr = threads->new(sub{
     lock $mutex;
     my $el = $doc->createElement('foo');
     # ...
    1;
  });
  {
    lock $mutex;
    my $root = $doc->documentElement;
    say $root->name;
  }
  $thr->join;

Note that libxml2 uses dictionaries to store short strings and these
dictionaries are kept on a document node. Without mutex locks, it could happen
in the previous example that the thread modifies the dictionary while other
threads attempt to read from it, which could easily lead to a crash.

=head1 VERSION INFORMATION

Sometimes it is useful to figure out, for which version XML::LibXML was
compiled for. In most cases this is for debugging or to check if a given
installation meets all functionality for the package. The functions
XML::LibXML::LIBXML_DOTTED_VERSION and XML::LibXML::LIBXML_VERSION provide this
version information. Both functions simply pass through the values of the
similar named macros of libxml2. Similarly, XML::LibXML::LIBXML_RUNTIME_VERSION
returns the version of the (usually dynamically) linked libxml2.

=over 4

=item XML::LibXML::LIBXML_DOTTED_VERSION

$Version_String = XML::LibXML::LIBXML_DOTTED_VERSION;

Returns the version string of the libxml2 version XML::LibXML was compiled for.
This will be "2.6.2" for "libxml2 2.6.2".

=item XML::LibXML::LIBXML_VERSION

$Version_ID = XML::LibXML::LIBXML_VERSION;

Returns the version id of the libxml2 version XML::LibXML was compiled for.
This will be "20602" for "libxml2 2.6.2". Don't mix this version id with
$XML::LibXML::VERSION. The latter contains the version of XML::LibXML itself
while the first contains the version of libxml2 XML::LibXML was compiled for.

=item XML::LibXML::LIBXML_RUNTIME_VERSION

$DLL_Version = XML::LibXML::LIBXML_RUNTIME_VERSION;

Returns a version string of the libxml2 which is (usually dynamically) linked
by XML::LibXML. This will be "20602" for libxml2 released as "2.6.2" and
something like "20602-CVS2032" for a CVS build of libxml2.

XML::LibXML issues a warning if the version of libxml2 dynamically linked to it
is less than the version of libxml2 which it was compiled against.

=back

=head1 EXPORTS

By default the module exports all constants and functions listed in the :all
tag, described below.

=head1 EXPORT TAGS

=over 4

=item C<<<<<< :all >>>>>>

Includes the tags C<<<<<< :libxml >>>>>>, C<<<<<< :encoding >>>>>>, and C<<<<<< :ns >>>>>> described below.

=item C<<<<<< :libxml >>>>>>

Exports integer constants for DOM node types.

XML_ELEMENT_NODE            => 1
  XML_ATTRIBUTE_NODE          => 2
  XML_TEXT_NODE               => 3
  XML_CDATA_SECTION_NODE      => 4
  XML_ENTITY_REF_NODE         => 5
  XML_ENTITY_NODE             => 6
  XML_PI_NODE                 => 7
  XML_COMMENT_NODE            => 8
  XML_DOCUMENT_NODE           => 9
  XML_DOCUMENT_TYPE_NODE      => 10
  XML_DOCUMENT_FRAG_NODE      => 11
  XML_NOTATION_NODE           => 12
  XML_HTML_DOCUMENT_NODE      => 13
  XML_DTD_NODE                => 14
  XML_ELEMENT_DECL            => 15
  XML_ATTRIBUTE_DECL          => 16
  XML_ENTITY_DECL             => 17
  XML_NAMESPACE_DECL          => 18
  XML_XINCLUDE_START          => 19
  XML_XINCLUDE_END            => 20

=item C<<<<<< :encoding >>>>>>

Exports two encoding conversion functions from XML::LibXML::Common.

encodeToUTF8()
  decodeFromUTF8()

=item C<<<<<< :ns >>>>>>

Exports two convenience constants: the implicit namespace of the reserved C<<<<<< xml: >>>>>> prefix, and the implicit namespace for the reserved C<<<<<< xmlns: >>>>>> prefix.

XML_XML_NS    => 'http://www.w3.org/XML/1998/namespace'
  XML_XMLNS_NS  => 'http://www.w3.org/2000/xmlns/'

=back

=head1 RELATED MODULES

The modules described in this section are not part of the XML::LibXML package
itself. As they support some additional features, they are mentioned here.

=over 4

=item L<<<<<< XML::LibXSLT >>>>>>

XSLT 1.0 Processor using libxslt and XML::LibXML

=item L<<<<<< XML::LibXML::Iterator >>>>>>

XML::LibXML Implementation of the DOM Traversal Specification

=item L<<<<<< XML::CompactTree::XS >>>>>>

Uses XML::LibXML::Reader to very efficiently to parse XML document or element
into native Perl data structures, which are less flexible but significantly
faster to process then DOM.

=back

=head1 XML::LIBXML AND XML::GDOME

Note: I<<<<<< THE FUNCTIONS DESCRIBED HERE ARE STILL EXPERIMENTAL >>>>>>

Although both modules make use of libxml2's XML capabilities, the DOM
implementation of both modules are not compatible. But still it is possible to
exchange nodes from one DOM to the other. The concept of this exchange is
pretty similar to the function cloneNode(): The particular node is copied on
the low-level to the opposite DOM implementation.

Since the DOM implementations cannot coexist within one document, one is forced
to copy each node that should be used. Because you are always keeping two nodes
this may cause quite an impact on a machines memory usage.

XML::LibXML provides two functions to export or import GDOME nodes:
import_GDOME() and export_GDOME(). Both function have two parameters: the node
and a flag for recursive import. The flag works as in cloneNode().

The two functions allow one to export and import XML::GDOME nodes explicitly,
however, XML::LibXML also allows the transparent import of XML::GDOME nodes in
functions such as appendChild(), insertAfter() and so on. While native nodes
are automatically adopted in most functions XML::GDOME nodes are always cloned
in advance. Thus if the original node is modified after the operation, the node
in the XML::LibXML document will not have this information.

=over 4

=item import_GDOME

$libxmlnode = XML::LibXML->import_GDOME( $node, $deep );

This clones an XML::GDOME node to an XML::LibXML node explicitly.

=item export_GDOME

$gdomenode = XML::LibXML->export_GDOME( $node, $deep );

Allows one to clone an XML::LibXML node into an XML::GDOME node.

=back

=head1 CONTACTS

For bug reports, please use the CPAN request tracker on
http://rt.cpan.org/NoAuth/Bugs.html?Dist=XML-LibXML

For suggestions etc., and other issues related to XML::LibXML you may use the
perl XML mailing list (C<<<<<< perl-xml@listserv.ActiveState.com >>>>>>), where most XML-related Perl modules are discussed. In case of problems you
should check the archives of that list first. Many problems are already
discussed there. You can find the list's archives and subscription options at L<<<<<< http://aspn.activestate.com/ASPN/Mail/Browse/Threaded/perl-xml >>>>>>.

=head1 AUTHORS

Matt Sergeant,
Christian Glahn,
Petr Pajas

=head1 VERSION

2.0210

=head1 COPYRIGHT

2001-2007, AxKit.com Ltd.

2002-2006, Christian Glahn.

2006-2009, Petr Pajas.

=cut

=head1 LICENSE

This program is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.

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