1XML::LibXML::DOM(3) User Contributed Perl Documentation XML::LibXML::DOM(3)
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6 XML::LibXML::DOM - XML::LibXML DOM Implementation
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9 XML::LibXML provides an lightwight interface to modify a node of the
10 document tree generated by the XML::LibXML parser. This interface fol‐
11 lows as far as possible the DOM Level 3 specification. Additionally to
12 the specified functions the XML::LibXML supports some functions that
13 are more handy to use in the perl environment.
14 One also has to remember, that XML::LibXML is an interface to libxml2
16 nodes which actually reside on the C-Level of XML::LibXML. This means
17 each node is a reference to a structure different than a perl hash or
18 array. The only way to access these structure's values is through the
19 DOM interface provided by XML::LibXML. This also means, that one can't
20 simply inherit a XML::LibXML node and add new member variables as they
21 were hash keys.
22 The DOM interface of XML::LibXML does not intend to implement a full
24 DOM interface as it is done by XML::GDOME and used for full featured
25 application. Moreover, it offers an simple way to build or modify doc‐
26 uments that are created by XML::LibXML's parser.
27 Another target of the XML::LibXML interface is to make the interfaces
29 of libxml2 available to the perl community. This includes also some
30 workarounds to some features where libxml2 assumes more control over
31 the C-Level that most perl users don't have.
32 One of the most important parts of the XML::LibXML DOM interface is,
34 that the interfaces try do follow the DOM Level 3 specification rather
35 strictly. This means the interface functions are named as the DOM spec‐
36 ification says and not what widespread Java interfaces claim to be
37 standard. Although there are several functions that have only a singu‐
38 lar interface that conforms to the DOM spec XML::LibXML provides an
39 additional Java style alias interface.
40 Also there are some function interfaces left over from early stages of
42 XML::LibXML for compatibility reasons. These interfaces are for compat‐
43 ibility reasons only. They might disappear in one of the future ver‐
44 sions of XML::LibXML, so a user is requested to switch over to the
45 official functions.
46 More recent versions of perl (e.g. 5.6.1 or higher) support special
48 flags to disinguish between UTF-8 and so called binary data.
49 XML::LibXML provides for these versions functionality to make efficient
50 use of these flags: If a document has set an encoding other than UTF-8
51 all strings that are not already in UTF-8 are implicitly encoded from
52 the document encoding to UTF-8. On output these strings are commonly
53 returned as UTF-8 unless a user does request explicitly the original
54 (aka. document) encoding.
55 Older version of perl (such as 5.00503 or less) do not support these
57 flags. If XML::LibXML is build for these versions, all strings have to
58 get encoded to UTF-8 manualy before they are passed to any DOM func‐
59 tions.
60 NOTE: XML::LibXML's magic encoding may not work on all plattforms. Some
62 platforms are known to have a broken iconv(), which is partly used by
63 libxml2. To test if your platform works correctly with your language
64 encoding, build a simple document in the particular encoding and try to
65 parse it with XML::LibXML. If your document gets parsed with out caus‐
66 ing any segmentation faults, bus errors or whatever your OS throws. An
67 example for such a test can be found in test 19encoding.t of the dis‐
68 tribution.
69 Namespaces and XML::LibXML's DOM implementation
71 XML::LibXML's DOM implementation is limitted by the DOM implementation
73 of libxml2 which treats namespaces slightly differently than required
74 by the DOM Level 2 specification.
75 According to the DOM Level 2 specification, namespaces of elements and
77 attributes should be persistent, and nodes should be permanently bound
78 to namespace URIs as they get created; it should be possible to manipu‐
79 late the special attributes used for declaring XML namespaces just as
80 other attributes without affecting the namespaces of other nodes. In
81 DOM Level 2, the application is responsible for creating the special
82 attributes consistently and/or for correct serialization of the docu‐
83 ment.
84 This is both unconvenient, causes problems in serialization of DOM to
86 XML, and most importantly, seems almost impossible to implement over
87 libxml2.
88 In libxml2, namespace URI and prefix of a node is provided by a pointer
90 to a namespace declaration (appearing as a special xmlns attribute in
91 the XML document). If the prefix or namespace URI of the declaration
92 changes, the prefix and namespace URI of all nodes that point to it
93 changes as well. Moreover, in contrast to DOM, a node (element or
94 attribute) can only be bound to a namespace URI if there is some names‐
95 pace declaration in the document to point to.
96 Therefore current DOM implementation in XML::LibXML tries to treat
98 namespace declarations in a compromise between reason, common sense,
99 limitations of libxml2, and the DOM Level 2 specification.
100 In XML::LibXML, special attributes declaring XML namespaces are often
102 created automatically, usually when a namespaced node is attached to a
103 document and no existing declaration of the namespace and prefix is in
104 the scope to be reused. In this respect, XML::LibXML DOM implementa‐
105 tion differs from the DOM Level 2 specification according to which spe‐
106 cial attributes for declaring the appropriate XML namespaces should not
107 be added when a node with a namespace prefix and namespace URI is cre‐
108 ated.
109 Namespace declarations are also created when XML::LibXML::Document's
111 createElementNS() or createAttributeNS() function are used. If the a
112 namespace is not declared on the documentElement, the namespace will be
113 localy declared for the newly created node. In case of Attributes this
114 may look a bit confusing, since these nodes cannot have namespace dec‐
115 larations itself. In this case the namespace is internally applied to
116 the attribute and later declared on the node the attribute is appended
117 to (if required).
118 The following example may explain this a bit:
120 my $doc = XML::LibXML->createDocument;
122 my $root = $doc->createElementNS( "", "foo" );
123 $doc->setDocumentElement( $root );
124 my $attr = $doc->createAttributeNS( "bar", "bar:foo", "test" );
126 $root->setAttributeNodeNS( $attr );
127 This piece of code will result in the following document:
129 <?xml version="1.0"?>
131 <foo xmlns:bar="bar" bar:foo="test"/>
132 The namespace is declared on the document element during the setAt‐
134 tributeNodeNS() call.
135 Namespaces can be also declared explicitly by the use of
137 XML::LibXML:Element's setNamespace() function. Since 1.61, they can
138 also be manipulated with functions setNamespaceDeclPrefix() and set‐
139 NamespaceDeclURI() (not available in DOM). Changing an URI or prefix of
140 an existing namespace declaration affects the namespace URI and prefix
141 of all nodes which point to it (that is the nodes in its scope).
142 It is also important to repeat the specification: While working with
144 namespaces you should use the namespace aware functions instead of the
145 simplified versions. For example you should never use setAttribute()
146 but setAttributeNS().
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149 Matt Sergeant, Christian Glahn, Petr Pajas,
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152 1.62
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155 2001-2006, AxKit.com Ltd; 2002-2006 Christian Glahn; 2006 Petr Pajas,
156 All rights reserved.
157perl v5.8.8 2006-11-17 XML::LibXML::DOM(3)