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->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<<<<<< <?xml version="1.0" encoding="..."?> >>>>>> declaration. Here is an example to follow:
use XML::LibXML;
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);
open my $out, "out.xml";
binmode $fh; # as above
$doc->toFh($fh);
# or
print $fh $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 apropriate
<?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 a
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, oaralel 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->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
dicionaries 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.
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.
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 >>>>>>.