phpman > perldoc > XML::LibXML::DOM(3pm)

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

DESCRIPTION
    XML::LibXML provides a lightweight 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. In addition to the specified functions, 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 which
    is different from a perl hash or array. The only way to access these structures' values is
    through the DOM interface provided by XML::LibXML. This also means, that one *can't* simply
    inherit an XML::LibXML node and add new member variables as if 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 to
    follow the DOM Level 3 specification (<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 the 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.

    Moreover, 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 document.

    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 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 appropriate 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().

AUTHORS
    Matt Sergeant, Christian Glahn, Petr Pajas

VERSION
    2.0134

COPYRIGHT
    2001-2007, AxKit.com Ltd.

    2002-2006, Christian Glahn.

    2006-2009, Petr Pajas.

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