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XML::LibXML::DOM(3)   User Contributed Perl Documentation  XML::LibXML::DOM(3)

       XML::LibXML::DOM - XML::LibXML DOM Implementation

       XML::LibXML provides an light-wight interface to modify a node of the
       document tree generated by the XML::LibXML parser. This interface
       follows 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
       documents 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
       (http://www.w3.org/TR/DOM-Level-3-Core/ <http://www.w3.org/TR/DOM-
       Level-3-Core/>) rather strictly. This means the interface functions are
       named as the DOM specification says and not what widespread Java
       interfaces claim to be standard. Although there are several functions
       that have only a singular 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
       compatibility reasons only. They might disappear in one of the future
       versions of XML::LibXML, so a user is requested to switch over to the
       official functions.

   Encodings and XML::LibXML's DOM implementation
       See the section on Encodings in the XML::LibXML manual page.

   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
       manipulate 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

       This is both inconvenient, causes problems in serialization of DOM to
       XML, and most importantly, seems almost impossible to implement over

       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
       namespace 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
       implementation differs from the DOM Level 2 specification according to
       which special attributes for declaring the apropriate XML namespaces
       should not be added when a node with a namespace prefix and namespace
       URI is created.

       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
       declarations 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
       setAttributeNodeNS() 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
       setNamespaceDeclURI() (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().

       Matt Sergeant, Christian Glahn, Petr Pajas


       2001-2007, AxKit.com Ltd.

       2002-2006, Christian Glahn.

       2006-2009, Petr Pajas.

perl v5.12.1                      2009-10-07               XML::LibXML::DOM(3)

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