XML::DOM - A perl module for building DOM Level 1 compliant document structures
use XML::DOM;
my $parser = new XML::DOM::Parser;
my $doc = $parser->parsefile ("file.xml");
# print all HREF attributes of all CODEBASE elements
my $nodes = $doc->getElementsByTagName ("CODEBASE");
my $n = $nodes->getLength;
for (my $i = 0; $i < $n; $i++)
{
my $node = $nodes->item ($i);
my $href = $node->getAttributeNode ("HREF");
print $href->getValue . "\n";
}
# Print doc file
$doc->printToFile ("out.xml");
# Print to string
print $doc->toString;
# Avoid memory leaks - cleanup circular references for garbage collection
$doc->dispose;
This module extends the XML::Parser module by Clark Cooper. The XML::Parser
module is built on top of XML::Parser::Expat, which is a lower level interface
to James Clark's expat library.
XML::DOM::Parser is derived from XML::Parser. It parses XML
strings or files and builds a data structure that conforms to the API of the
Document Object Model as described at http://www.w3.org/TR/REC-DOM-Level-1.
See the XML::Parser manpage for other available features of the
XML::DOM::Parser class. Note that the 'Style' property should not be used
(it is set internally.)
The XML::Parser NoExpand option is more or less supported,
in that it will generate EntityReference objects whenever an entity
reference is encountered in character data. I'm not sure how useful this is.
Any comments are welcome.
As described in the synopsis, when you create an XML::DOM::Parser
object, the parse and parsefile methods create an XML::DOM::Document
object from the specified input. This Document object can then be examined,
modified and written back out to a file or converted to a string.
When using XML::DOM with XML::Parser version 2.19 and up, setting
the XML::DOM::Parser option KeepCDATA to 1 will store CDATASections
in CDATASection nodes, instead of converting them to Text nodes. Subsequent
CDATASection nodes will be merged into one. Let me know if this is a
problem.
When using XML::Parser 2.27 and above, you can suppress expansion
of parameter entity references (e.g. %pent;) in the
DTD, by setting ParseParamEnt to 1 and ExpandParamEnt to 0.
See Hidden Nodes for details.
A Document has a tree structure consisting of Node objects.
A Node may contain other nodes, depending on its type. A Document may have
Element, Text, Comment, and CDATASection nodes. Element nodes may have Attr,
Element, Text, Comment, and CDATASection nodes. The other nodes may not have
any child nodes.
This module adds several node types that are not part of the DOM
spec (yet.) These are: ElementDecl (for <!ELEMENT ...> declarations),
AttlistDecl (for <!ATTLIST ...> declarations), XMLDecl (for <?xml
...?> declarations) and AttDef (for attribute definitions in an
AttlistDecl.)
The XML::DOM module stores XML documents in a tree structure with a root node of
type XML::DOM::Document. Different nodes in tree represent different parts of
the XML file. The DOM Level 1 Specification defines the following node types:
- XML::DOM::Node - Super class of all node types
- XML::DOM::Document - The root of the XML document
- XML::DOM::DocumentType - Describes the document structure: <!DOCTYPE
root [ ... ]>
- XML::DOM::Element - An XML element: <elem attr="val"> ...
</elem>
- XML::DOM::Attr - An XML element attribute: name="value"
- XML::DOM::CharacterData - Super class of Text, Comment and
CDATASection
- XML::DOM::Text - Text in an XML element
- XML::DOM::CDATASection - Escaped block of text: <![CDATA[ text
]]>
- XML::DOM::Comment - An XML comment: <!-- comment -->
- XML::DOM::EntityReference - Refers to an ENTITY: &ent; or
%ent;
- XML::DOM::Entity - An ENTITY definition: <!ENTITY ...>
- XML::DOM::ProcessingInstruction - <?PI target>
- XML::DOM::DocumentFragment - Lightweight node for cut & paste
- XML::DOM::Notation - An NOTATION definition: <!NOTATION ...>
In addition, the XML::DOM module contains the following nodes that
are not part of the DOM Level 1 Specification:
- XML::DOM::ElementDecl - Defines an element: <!ELEMENT ...>
- XML::DOM::AttlistDecl - Defines one or more attributes in an <!ATTLIST
...>
- XML::DOM::AttDef - Defines one attribute in an <!ATTLIST ...>
- XML::DOM::XMLDecl - An XML declaration: <?xml version="1.0"
...>
Other classes that are part of the DOM Level 1 Spec:
- XML::DOM::Implementation - Provides information about this implementation.
Currently it doesn't do much.
- XML::DOM::NodeList - Used internally to store a node's child nodes. Also
returned by getElementsByTagName.
- XML::DOM::NamedNodeMap - Used internally to store an element's
attributes.
Other classes that are not part of the DOM Level 1 Spec:
- XML::DOM::Parser - An non-validating XML parser that creates
XML::DOM::Documents
- XML::DOM::ValParser - A validating XML parser that creates
XML::DOM::Documents. It uses XML::Checker to check against the
DocumentType (DTD)
- XML::Handler::BuildDOM - A PerlSAX handler that creates
XML::DOM::Documents.
- Constant definitions
- The following predefined constants indicate which type of node it is.
UNKNOWN_NODE (0) The node type is unknown (not part of DOM)
ELEMENT_NODE (1) The node is an Element.
ATTRIBUTE_NODE (2) The node is an Attr.
TEXT_NODE (3) The node is a Text node.
CDATA_SECTION_NODE (4) The node is a CDATASection.
ENTITY_REFERENCE_NODE (5) The node is an EntityReference.
ENTITY_NODE (6) The node is an Entity.
PROCESSING_INSTRUCTION_NODE (7) The node is a ProcessingInstruction.
COMMENT_NODE (8) The node is a Comment.
DOCUMENT_NODE (9) The node is a Document.
DOCUMENT_TYPE_NODE (10) The node is a DocumentType.
DOCUMENT_FRAGMENT_NODE (11) The node is a DocumentFragment.
NOTATION_NODE (12) The node is a Notation.
ELEMENT_DECL_NODE (13) The node is an ElementDecl (not part of DOM)
ATT_DEF_NODE (14) The node is an AttDef (not part of DOM)
XML_DECL_NODE (15) The node is an XMLDecl (not part of DOM)
ATTLIST_DECL_NODE (16) The node is an AttlistDecl (not part of DOM)
Usage:
if ($node->getNodeType == ELEMENT_NODE)
{
print "It's an Element";
}
Not In DOM Spec: The DOM Spec does not mention UNKNOWN_NODE
and, quite frankly, you should never encounter it. The last 4 node types
were added to support the 4 added node classes.
- $VERSION
- The variable $XML::DOM::VERSION contains the
version number of this implementation, e.g. "1.07".
These methods are not part of the DOM Level 1 Specification.
- getIgnoreReadOnly and ignoreReadOnly (readOnly)
- The DOM Level 1 Spec does not allow you to edit certain sections of the
document, e.g. the DocumentType, so by default this implementation throws
DOMExceptions (i.e. NO_MODIFICATION_ALLOWED_ERR) when you try to edit a
readonly node. These readonly checks can be disabled by (temporarily)
setting the global IgnoreReadOnly flag.
The ignoreReadOnly method sets the global IgnoreReadOnly flag
and returns its previous value. The getIgnoreReadOnly method simply
returns its current value.
my $oldIgnore = XML::DOM::ignoreReadOnly (1);
eval {
... do whatever you want, catching any other exceptions ...
};
XML::DOM::ignoreReadOnly ($oldIgnore); # restore previous value
Another way to do it, using a local variable:
{ # start new scope
local $XML::DOM::IgnoreReadOnly = 1;
... do whatever you want, don't worry about exceptions ...
} # end of scope ($IgnoreReadOnly is set back to its previous value)
- isValidName (name)
- Whether the specified name is a valid "Name" as specified in the
XML spec. Characters with Unicode values > 127 are now also
supported.
- getAllowReservedNames and allowReservedNames (boolean)
- The first method returns whether reserved names are allowed. The second
takes a boolean argument and sets whether reserved names are allowed. The
initial value is 1 (i.e. allow reserved names.)
The XML spec states that "Names" starting with
(X|x)(M|m)(L|l) are reserved for future use. (Amusingly enough, the XML
version of the XML spec (REC-xml-19980210.xml) breaks that very rule by
defining an ENTITY with the name 'xmlpio'.) A "Name" in this
context means the Name token as found in the BNF rules in the XML
spec.
XML::DOM only checks for errors when you modify the DOM tree,
not when the DOM tree is built by the XML::DOM::Parser.
- setTagCompression (funcref)
- There are 3 possible styles for printing empty Element tags:
- Style 0
-
<empty/> or <empty attr="val"/>
XML::DOM uses this style by default for all Elements.
- Style 1
-
<empty></empty> or <empty attr="val"></empty>
- Style 2
-
<empty /> or <empty attr="val" />
This style is sometimes desired when using XHTML. (Note the
extra space before the slash "/") See
<http://www.w3.org/TR/xhtml1> Appendix C for more details.
By default XML::DOM compresses all empty Element tags (style 0.)
You can control which style is used for a particular Element by calling
XML::DOM::setTagCompression with a reference to a function that takes 2
arguments. The first is the tag name of the Element, the second is the
XML::DOM::Element that is being printed. The function should return 0, 1 or
2 to indicate which style should be used to print the empty tag. E.g.
XML::DOM::setTagCompression (\&my_tag_compression);
sub my_tag_compression
{
my ($tag, $elem) = @_;
# Print empty br, hr and img tags like this: <br />
return 2 if $tag =~ /^(br|hr|img)$/;
# Print other empty tags like this: <empty></empty>
return 1;
}
- Perl Mappings
The value undef was used when the DOM Spec said null.
The DOM Spec says: Applications must encode DOMString using
UTF-16 (defined in Appendix C.3 of [UNICODE] and Amendment 1 of
[ISO-10646]). In this implementation we use plain old Perl strings
encoded in UTF-8 instead of UTF-16.
- Text and CDATASection nodes
The Expat parser expands EntityReferences and CDataSection
sections to raw strings and does not indicate where it was found. This
implementation does therefore convert both to Text nodes at parse time.
CDATASection and EntityReference nodes that are added to an existing
Document (by the user) will be preserved.
Also, subsequent Text nodes are always merged at parse time.
Text nodes that are added later can be merged with the normalize method.
Consider using the addText method when adding Text nodes.
- Printing and toString
When printing (and converting an XML Document to a string) the
strings have to encoded differently depending on where they occur. E.g.
in a CDATASection all substrings are allowed except for
"]]>". In regular text, certain characters are not allowed,
e.g. ">" has to be converted to ">". These
routines should be verified by someone who knows the details.
- Quotes
Certain sections in XML are quoted, like attribute values in
an Element. XML::Parser strips these quotes and the print methods in
this implementation always uses double quotes, so when parsing and
printing a document, single quotes may be converted to double quotes.
The default value of an attribute definition (AttDef) in an AttlistDecl,
however, will maintain its quotes.
- AttlistDecl
Attribute declarations for a certain Element are always merged
into a single AttlistDecl object.
- Comments
Comments in the DOCTYPE section are not kept in the right
place. They will become child nodes of the Document.
- Hidden Nodes
Previous versions of XML::DOM would expand parameter entity
references (like %pent;), so when printing the DTD,
it would print the contents of the external entity, instead of the
parameter entity reference. With this release (1.27), you can prevent
this by setting the XML::DOM::Parser options ParseParamEnt => 1 and
ExpandParamEnt => 0.
When it is parsing the contents of the external entities, it
*DOES* still add the nodes to the DocumentType, but it marks these nodes
by setting the 'Hidden' property. In addition, it adds an
EntityReference node to the DocumentType node.
When printing the DocumentType node (or when using
to_expat() or to_sax()), the 'Hidden' nodes are
suppressed, so you will see the parameter entity reference instead of
the contents of the external entities. See test case t/dom_extent.t for
an example.
The reason for adding the 'Hidden' nodes to the DocumentType
node, is that the nodes may contain <!ENTITY> definitions that are
referenced further in the document. (Simply not adding the nodes to the
DocumentType could cause such entity references to be expanded
incorrectly.)
Note that you need XML::Parser 2.27 or higher for this to work
correctly.
The Japanese version of this document by Takanori Kawai (Hippo2000) at
<http://member.nifty.ne.jp/hippo2000/perltips/xml/dom.htm>
The DOM Level 1 specification at
<http://www.w3.org/TR/REC-DOM-Level-1>
The XML spec (Extensible Markup Language 1.0) at
<http://www.w3.org/TR/REC-xml>
The XML::Parser and XML::Parser::Expat manual pages.
The method getElementsByTagName() does not return a "live"
NodeList. Whether this is an actual caveat is debatable, but a few people on
the www-dom mailing list seemed to think so. I haven't decided yet. It's a
pain to implement, it slows things down and the benefits seem marginal. Let me
know what you think.
(To subscribe to the www-dom mailing list send an email with the
subject "subscribe" to www-dom-request@w3.org. I only look here
occasionally, so don't send bug reports or suggestions about XML::DOM to
this list, send them to enno@att.com instead.)
Send bug reports, hints, tips, suggestions to Enno Derksen at
<enno@att.com>.
Thanks to Clark Cooper for his help with the initial version.