XML::LibXML::DOM(3) User Contributed Perl Documentation XML::LibXML::DOM(3)NAMEXML::LibXML::DOM - XML::LibXML DOM Implementation
DESCRIPTION
XML::LibXML provides an light-wight interface to modify a node of the
document tree generated by the XML::LibXML parser. This interface fol-
lows as far as possible the DOM Level 3 specification. Additionally to
the specified functions the XML::LibXML supports some functions that
are more handy to use in the perl environment.
One also has to remember, that XML::LibXML is an interface to libxml2
nodes which actually reside on the C-Level of XML::LibXML. This means
each node is a reference to a structure different than a perl hash or
array. The only way to access these structure's values is through the
DOM interface provided by XML::LibXML. This also means, that one can't
simply inherit a XML::LibXML node and add new member variables as they
were hash keys.
The DOM interface of XML::LibXML does not intend to implement a full
DOM interface as it is done by XML::GDOME and used for full featured
application. Moreover, it offers an simple way to build or modify doc-
uments that are created by XML::LibXML's parser.
Another target of the XML::LibXML interface is to make the interfaces
of libxml2 available to the perl community. This includes also some
workarounds to some features where libxml2 assumes more control over
the C-Level that most perl users don't have.
One of the most important parts of the XML::LibXML DOM interface is,
that the interfaces try do follow the DOM Level 3 specification rather
strictly. This means the interface functions are named as the DOM spec-
ification says and not what widespread Java interfaces claim to be
standard. Although there are several functions that have only a singu-
lar interface that conforms to the DOM spec XML::LibXML provides an
additional Java style alias interface.
Also there are some function interfaces left over from early stages of
XML::LibXML for compatibility reasons. These interfaces are for compat-
ibility reasons only. They might disappear in one of the future ver-
sions of XML::LibXML, so a user is requested to switch over to the
official functions.
More recent versions of perl (e.g. 5.6.1 or higher) support special
flags to distinguish between UTF-8 and so called binary data.
XML::LibXML provides for these versions functionality to make efficient
use of these flags: If a document has set an encoding other than UTF-8
all strings that are not already in UTF-8 are implicitly encoded from
the document encoding to UTF-8. On output these strings are commonly
returned as UTF-8 unless a user does request explicitly the original
(aka. document) encoding.
Older version of perl (such as 5.00503 or less) do not support these
flags. If XML::LibXML is build for these versions, all strings have to
get encoded to UTF-8 manually before they are passed to any DOM func-
tions.
NOTE: XML::LibXML's magic encoding may not work on all platforms. Some
platforms are known to have a broken iconv(), which is partly used by
libxml2. 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. If your document gets parsed with out caus-
ing any segmentation faults, bus errors or whatever your OS throws. An
example for such a test can be found in test 19encoding.t of the dis-
tribution.
Namespaces and XML::LibXML's DOM implementation
XML::LibXML's DOM implementation is limited by the DOM implementation
of libxml2 which treats namespaces slightly differently than required
by the DOM Level 2 specification.
According to the DOM Level 2 specification, namespaces of elements and
attributes should be persistent, and nodes should be permanently bound
to namespace URIs as they get created; it should be possible to manipu-
late the special attributes used for declaring XML namespaces just as
other attributes without affecting the namespaces of other nodes. In
DOM Level 2, the application is responsible for creating the special
attributes consistently and/or for correct serialization of the docu-
ment.
This is both inconvenient, causes problems in serialization of DOM to
XML, and most importantly, seems almost impossible to implement over
libxml2.
In libxml2, namespace URI and prefix of a node is provided by a pointer
to a namespace declaration (appearing as a special xmlns attribute in
the XML document). If the prefix or namespace URI of the declaration
changes, the prefix and namespace URI of all nodes that point to it
changes as well. Moreover, in contrast to DOM, a node (element or
attribute) can only be bound to a namespace URI if there is some names-
pace declaration in the document to point to.
Therefore current DOM implementation in XML::LibXML tries to treat
namespace declarations in a compromise between reason, common sense,
limitations of libxml2, and the DOM Level 2 specification.
In XML::LibXML, special attributes declaring XML namespaces are often
created automatically, usually when a namespaced node is attached to a
document and no existing declaration of the namespace and prefix is in
the scope to be reused. In this respect, XML::LibXML DOM implementa-
tion differs from the DOM Level 2 specification according to which spe-
cial attributes for declaring the appropriate XML namespaces should not
be added when a node with a namespace prefix and namespace URI is cre-
ated.
Namespace declarations are also created when XML::LibXML::Document's
createElementNS() or createAttributeNS() function are used. If the a
namespace is not declared on the documentElement, the namespace will be
locally declared for the newly created node. In case of Attributes this
may look a bit confusing, since these nodes cannot have namespace dec-
larations itself. In this case the namespace is internally applied to
the attribute and later declared on the node the attribute is appended
to (if required).
The following example may explain this a bit:
my $doc = XML::LibXML->createDocument;
my $root = $doc->createElementNS( "", "foo" );
$doc->setDocumentElement( $root );
my $attr = $doc->createAttributeNS( "bar", "bar:foo", "test" );
$root->setAttributeNodeNS( $attr );
This piece of code will result in the following document:
<?xml version="1.0"?>
<foo xmlns:bar="bar" bar:foo="test"/>
The namespace is declared on the document element during the setAt-
tributeNodeNS() call.
Namespaces can be also declared explicitly by the use of
XML::LibXML:Element's setNamespace() function. Since 1.61, they can
also be manipulated with functions setNamespaceDeclPrefix() and set-
NamespaceDeclURI() (not available in DOM). Changing an URI or prefix of
an existing namespace declaration affects the namespace URI and prefix
of all nodes which point to it (that is the nodes in its scope).
It is also important to repeat the specification: While working with
namespaces you should use the namespace aware functions instead of the
simplified versions. For example you should never use setAttribute()
but setAttributeNS().
AUTHORS
Matt Sergeant, Christian Glahn, Petr Pajas,
VERSION
1.63
COPYRIGHT
2001-2007, AxKit.com Ltd; 2002-2006 Christian Glahn; 2006-2007 Petr
Pajas, All rights reserved.
perl v5.8.8 2007-04-16 XML::LibXML::DOM(3)
