Страницы справочника OS X

Эта страница руководства для  версии 10.9 Mac OS X

Читать страницы руководства

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



NAME
       XML::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 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 an 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
       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
       2.0008

COPYRIGHT
       2001-2007, AxKit.com Ltd.

       2002-2006, Christian Glahn.

       2006-2009, Petr Pajas.



perl v5.16.2                                     2012-10-22                              XML::LibXML::DOM(3)