"xml.dom" — The Document Object Model API
*****************************************

**Source code:** Lib/xml/dom/__init__.py

======================================================================

The Document Object Model, or “DOM,” is a cross-language API from the
World Wide Web Consortium (W3C) for accessing and modifying XML
documents.  A DOM implementation presents an XML document as a tree
structure, or allows client code to build such a structure from
scratch.  It then gives access to the structure through a set of
objects which provided well-known interfaces.

The DOM is extremely useful for random-access applications.  SAX only
allows you a view of one bit of the document at a time.  If you are
looking at one SAX element, you have no access to another.  If you are
looking at a text node, you have no access to a containing element.
When you write a SAX application, you need to keep track of your
program’s position in the document somewhere in your own code.  SAX
does not do it for you.  Also, if you need to look ahead in the XML
document, you are just out of luck.

Some applications are simply impossible in an event driven model with
no access to a tree.  Of course you could build some sort of tree
yourself in SAX events, but the DOM allows you to avoid writing that
code.  The DOM is a standard tree representation for XML data.

The Document Object Model is being defined by the W3C in stages, or
“levels” in their terminology.  The Python mapping of the API is
substantially based on the DOM Level 2 recommendation.

DOM applications typically start by parsing some XML into a DOM.  How
this is accomplished is not covered at all by DOM Level 1, and Level 2
provides only limited improvements: There is a "DOMImplementation"
object class which provides access to "Document" creation methods, but
no way to access an XML reader/parser/Document builder in an
implementation-independent way. There is also no well-defined way to
access these methods without an existing "Document" object.  In
Python, each DOM implementation will provide a function
"getDOMImplementation()". DOM Level 3 adds a Load/Store specification,
which defines an interface to the reader, but this is not yet
available in the Python standard library.

Once you have a DOM document object, you can access the parts of your
XML document through its properties and methods.  These properties are
defined in the DOM specification; this portion of the reference manual
describes the interpretation of the specification in Python.

The specification provided by the W3C defines the DOM API for Java,
ECMAScript, and OMG IDL.  The Python mapping defined here is based in
large part on the IDL version of the specification, but strict
compliance is not required (though implementations are free to support
the strict mapping from IDL).  See section Conformance for a detailed
discussion of mapping requirements.

See also:

  Document Object Model (DOM) Level 2 Specification
     The W3C recommendation upon which the Python DOM API is based.

  Document Object Model (DOM) Level 1 Specification
     The W3C recommendation for the DOM supported by
     "xml.dom.minidom".

  Python Language Mapping Specification
     This specifies the mapping from OMG IDL to Python.


Module Contents
===============

The "xml.dom" contains the following functions:

xml.dom.registerDOMImplementation(name, factory)

   Register the *factory* function with the name *name*.  The factory
   function should return an object which implements the
   "DOMImplementation" interface.  The factory function can return the
   same object every time, or a new one for each call, as appropriate
   for the specific implementation (e.g. if that implementation
   supports some customization).

xml.dom.getDOMImplementation(name=None, features=())

   Return a suitable DOM implementation. The *name* is either well-
   known, the module name of a DOM implementation, or "None". If it is
   not "None", imports the corresponding module and returns a
   "DOMImplementation" object if the import succeeds.  If no name is
   given, and if the environment variable "PYTHON_DOM" is set, this
   variable is used to find the implementation. The only well-known
   name in the standard library is "'minidom'", for "xml.dom.minidom".

   If name is not given, this examines the available implementations
   to find one with the required feature set.  If no implementation
   can be found, raise an "ImportError".  The features list must be a
   sequence of "(feature, version)" pairs which are passed to the
   "hasFeature()" method on available "DOMImplementation" objects.

Some convenience constants are also provided:

xml.dom.EMPTY_NAMESPACE

   The value used to indicate that no namespace is associated with a
   node in the DOM.  This is typically found as the "namespaceURI" of
   a node, or used as the *namespaceURI* parameter to a namespaces-
   specific method.

xml.dom.XML_NAMESPACE

   The namespace URI associated with the reserved prefix "xml", as
   defined by Namespaces in XML (section 4).

xml.dom.XMLNS_NAMESPACE

   The namespace URI for namespace declarations, as defined by
   Document Object Model (DOM) Level 2 Core Specification (section
   1.1.8).

xml.dom.XHTML_NAMESPACE

   The URI of the XHTML namespace as defined by XHTML 1.0: The
   Extensible HyperText Markup Language (section 3.1.1).

In addition, "xml.dom" contains a base "Node" class and the DOM
exception classes.  The "Node" class provided by this module does not
implement any of the methods or attributes defined by the DOM
specification; concrete DOM implementations must provide those.  The
"Node" class provided as part of this module does provide the
constants used for the "nodeType" attribute on concrete "Node"
objects; they are located within the class rather than at the module
level to conform with the DOM specifications.


Objects in the DOM
==================

The definitive documentation for the DOM is the DOM specification from
the W3C.

The names documented in this section are DOM interfaces. With the
exception of "Node" and the exception classes, they are not provided
by the "xml.dom" module itself, but by concrete DOM implementations,
such as "xml.dom.minidom".

Note that DOM attributes may also be manipulated as nodes instead of
as simple strings.  It is fairly rare that you must do this, however,
so this usage is not yet documented.

+----------------------------------+-------------------------------------+-----------------------------------+
| Interface                        | Section                             | Purpose                           |
|==================================|=====================================|===================================|
| "DOMImplementation"              | DOMImplementation Objects           | Interface to the underlying       |
|                                  |                                     | implementation.                   |
+----------------------------------+-------------------------------------+-----------------------------------+
| "Node"                           | Node Objects                        | Base interface for most objects   |
|                                  |                                     | in a document.                    |
+----------------------------------+-------------------------------------+-----------------------------------+
| "NodeList"                       | NodeList Objects                    | Interface for a sequence of       |
|                                  |                                     | nodes.                            |
+----------------------------------+-------------------------------------+-----------------------------------+
| "DocumentType"                   | DocumentType Objects                | Information about the             |
|                                  |                                     | declarations needed to process a  |
|                                  |                                     | document.                         |
+----------------------------------+-------------------------------------+-----------------------------------+
| "Document"                       | Document Objects                    | Object which represents an entire |
|                                  |                                     | document.                         |
+----------------------------------+-------------------------------------+-----------------------------------+
| "Element"                        | Element Objects                     | Element nodes in the document     |
|                                  |                                     | hierarchy.                        |
+----------------------------------+-------------------------------------+-----------------------------------+
| "Attr"                           | Attr Objects                        | Attribute value nodes on element  |
|                                  |                                     | nodes.                            |
+----------------------------------+-------------------------------------+-----------------------------------+
| "Comment"                        | Comment Objects                     | Representation of comments in the |
|                                  |                                     | source document.                  |
+----------------------------------+-------------------------------------+-----------------------------------+
| "Text"                           | Text and CDATASection Objects       | Nodes containing textual content  |
|                                  |                                     | from the document.                |
+----------------------------------+-------------------------------------+-----------------------------------+
| "ProcessingInstruction"          | ProcessingInstruction Objects       | Processing instruction            |
|                                  |                                     | representation.                   |
+----------------------------------+-------------------------------------+-----------------------------------+

An additional section describes the exceptions defined for working
with the DOM in Python.


DOMImplementation Objects
-------------------------

The "DOMImplementation" interface provides a way for applications to
determine the availability of particular features in the DOM they are
using. DOM Level 2 added the ability to create new "Document" and
"DocumentType" objects using the "DOMImplementation" as well.

DOMImplementation.hasFeature(feature, version)

   Return "True" if the feature identified by the pair of strings
   *feature* and *version* is implemented.

DOMImplementation.createDocument(namespaceUri, qualifiedName, doctype)

   Return a new "Document" object (the root of the DOM), with a child
   "Element" object having the given *namespaceUri* and
   *qualifiedName*. The *doctype* must be a "DocumentType" object
   created by "createDocumentType()", or "None". In the Python DOM
   API, the first two arguments can also be "None" in order to
   indicate that no "Element" child is to be created.

DOMImplementation.createDocumentType(qualifiedName, publicId, systemId)

   Return a new "DocumentType" object that encapsulates the given
   *qualifiedName*, *publicId*, and *systemId* strings, representing
   the information contained in an XML document type declaration.


Node Objects
------------

All of the components of an XML document are subclasses of "Node".

Only nodes of the following types can have children, and only children
of the listed types:

"Document"
   at most one "Element", at most one "DocumentType",
   "ProcessingInstruction" and "Comment"

"DocumentFragment" and "Element"
   "Element", "Text", "CDATASection", "ProcessingInstruction" and
   "Comment"

"Attr"
   "Text"

Nodes of other types cannot have children. Inserting a child of a not
allowed type raises "HierarchyRequestErr".

Node.nodeType

   An integer representing the node type.  Symbolic constants for the
   types are on the "Node" object. This is a read-only attribute.

Node.ELEMENT_NODE
Node.ATTRIBUTE_NODE
Node.TEXT_NODE
Node.CDATA_SECTION_NODE
Node.ENTITY_REFERENCE_NODE
Node.ENTITY_NODE
Node.PROCESSING_INSTRUCTION_NODE
Node.COMMENT_NODE
Node.DOCUMENT_NODE
Node.DOCUMENT_TYPE_NODE
Node.DOCUMENT_FRAGMENT_NODE
Node.NOTATION_NODE

   Integer constants for the possible values of the "nodeType"
   attribute.

Node.parentNode

   The parent of the current node, or "None" for the document node.
   The value is always a "Node" object or "None".  For "Element"
   nodes, this will be the parent element, except for the root
   element, in which case it will be the "Document" object. For "Attr"
   nodes, this is always "None". This is a read-only attribute.

Node.attributes

   A "NamedNodeMap" of attribute objects.  Only elements have actual
   values for this; others provide "None" for this attribute. This is
   a read-only attribute.

Node.previousSibling

   The node that immediately precedes this one with the same parent.
   For instance the element with an end-tag that comes just before the
   *self* element’s start-tag.  Of course, XML documents are made up
   of more than just elements so the previous sibling could be text, a
   comment, or something else. If this node is the first child of the
   parent, this attribute will be "None". This is a read-only
   attribute.

Node.nextSibling

   The node that immediately follows this one with the same parent.
   See also "previousSibling".  If this is the last child of the
   parent, this attribute will be "None". This is a read-only
   attribute.

Node.childNodes

   A "NodeList" of the children of this node. If the node has no
   children, the list is empty. This is a read-only attribute.

Node.firstChild

   The first child of the node, if there are any, or "None". This is a
   read-only attribute.

Node.lastChild

   The last child of the node, if there are any, or "None". This is a
   read-only attribute.

Node.localName

   The part of the "tagName" following the colon if there is one, else
   the entire "tagName".  The value is a string.

Node.prefix

   The part of the "tagName" preceding the colon if there is one, else
   the empty string.  The value is a string, or "None".

Node.namespaceURI

   The namespace associated with the element name.  This will be a
   string or "None".  This is a read-only attribute.

Node.ownerDocument

   The "Document" object to which this node belongs, or "None" for a
   document itself. This is a read-only attribute.

Node.isSupported(feature, version)

   Return whether the DOM implementation supports a particular
   *feature*, as "DOMImplementation.hasFeature()" does.

Node.setUserData(key, data, handler)

   Associate *data* with *key* on this node and return the data
   previously associated with *key*, or "None". If *data* is "None",
   the association is removed. *handler* is called when the node is
   cloned, imported, renamed or deleted; pass "None" if no
   notification is needed.

Node.getUserData(key)

   Return the data associated with *key* on this node by
   "setUserData()", or "None".

Node.nodeName

   The name of this node, depending on its type; see the table below.
   You can always get the information you would get here from another
   property such as the "tagName" property for elements or the "name"
   property for attributes. This is a read-only attribute.

Node.nodeValue

   The value of this node, depending on its type; see the table below.
   The value is a string or "None".

The values of "nodeName" and "nodeValue" for each node type are:

+----------------------------------+-----------------------------------------+---------------------------------------+
| Node type                        | nodeName                                | nodeValue                             |
|==================================|=========================================|=======================================|
| "Attr"                           | "name"                                  | "value"                               |
+----------------------------------+-----------------------------------------+---------------------------------------+
| "CDATASection"                   | "'#cdata-section'"                      | the content                           |
+----------------------------------+-----------------------------------------+---------------------------------------+
| "Comment"                        | "'#comment'"                            | the content                           |
+----------------------------------+-----------------------------------------+---------------------------------------+
| "Document"                       | "'#document'"                           | "None"                                |
+----------------------------------+-----------------------------------------+---------------------------------------+
| "DocumentFragment"               | "'#document-fragment'"                  | "None"                                |
+----------------------------------+-----------------------------------------+---------------------------------------+
| "DocumentType"                   | "name"                                  | "None"                                |
+----------------------------------+-----------------------------------------+---------------------------------------+
| "Element"                        | "tagName"                               | "None"                                |
+----------------------------------+-----------------------------------------+---------------------------------------+
| "Entity"                         | the name of the entity                  | "None"                                |
+----------------------------------+-----------------------------------------+---------------------------------------+
| "Notation"                       | the name of the notation                | "None"                                |
+----------------------------------+-----------------------------------------+---------------------------------------+
| "ProcessingInstruction"          | "target"                                | "data"                                |
+----------------------------------+-----------------------------------------+---------------------------------------+
| "Text"                           | "'#text'"                               | the content                           |
+----------------------------------+-----------------------------------------+---------------------------------------+

Node.hasAttributes()

   Return "True" if the node has any attributes.

Node.hasChildNodes()

   Return "True" if the node has any child nodes.

Node.isSameNode(other)

   Return "True" if *other* refers to the same node as this node. This
   is especially useful for DOM implementations which use any sort of
   proxy architecture (because more than one object can refer to the
   same node).

   Note:

     This is based on a proposed DOM Level 3 API which is still in the
     “working draft” stage, but this particular interface appears
     uncontroversial.  Changes from the W3C will not necessarily
     affect this method in the Python DOM interface (though any new
     W3C API for this would also be supported).

Node.appendChild(newChild)

   Add a new child node to this node at the end of the list of
   children, returning *newChild*. If the node was already in the
   tree, it is removed first.

Node.insertBefore(newChild, refChild)

   Insert a new child node before an existing child.  It must be the
   case that *refChild* is a child of this node; if not, "NotFoundErr"
   is raised. *newChild* is returned. If *refChild* is "None", it
   inserts *newChild* at the end of the children’s list.

Node.removeChild(oldChild)

   Remove a child node.  *oldChild* must be a child of this node; if
   not, "NotFoundErr" is raised.  *oldChild* is returned on success.
   If *oldChild* will not be used further, its "unlink()" method
   should be called.

Node.replaceChild(newChild, oldChild)

   Replace an existing node with a new node. It must be the case that
   *oldChild* is a child of this node; if not, "NotFoundErr" is
   raised.

Node.normalize()

   Join adjacent text nodes so that all stretches of text are stored
   as single "Text" instances.  This simplifies processing text from a
   DOM tree for many applications.

Node.cloneNode(deep)

   Clone this node.  Setting *deep* means to clone all child nodes as
   well.  This returns the clone.


NodeList Objects
----------------

A "NodeList" represents a sequence of nodes.  These objects are used
in two ways in the DOM Core recommendation:  an "Element" object
provides one as its list of child nodes, and the
"getElementsByTagName()" and "getElementsByTagNameNS()" methods of
"Node" return objects with this interface to represent query results.

"NodeList" does *not* inherit from "Node".

The DOM Level 2 recommendation defines one method and one attribute
for these objects:

NodeList.item(i)

   Return the *i*’th item from the sequence, or "None" if *i* is out
   of range. Negative indices are not supported.

NodeList.length

   The number of nodes in the sequence.

In addition, the Python DOM interface requires that some additional
support is provided to allow "NodeList" objects to be used as Python
sequences.  All "NodeList" implementations must include support for
"__len__()" and "__getitem__()"; this allows iteration over the
"NodeList" in "for" statements and proper support for the "len()"
built-in function.

If a DOM implementation supports modification of the document, the
"NodeList" implementation must also support the "__setitem__()" and
"__delitem__()" methods.


DocumentType Objects
--------------------

Information about the notations and entities declared by a document
(including the external subset if the parser uses it and can provide
the information) is available from a "DocumentType" object.  The
"DocumentType" for a document is available from the "Document"
object’s "doctype" attribute; if there is no "DOCTYPE" declaration for
the document, the document’s "doctype" attribute will be set to "None"
instead of an instance of this interface.

"DocumentType" is a specialization of "Node", and adds the following
attributes:

DocumentType.publicId

   The public identifier for the external subset of the document type
   definition, or "None" if the "DOCTYPE" declaration does not specify
   it.

DocumentType.systemId

   The system identifier, a URI, for the external subset of the
   document type definition, or "None" if the "DOCTYPE" declaration
   does not specify it.

DocumentType.internalSubset

   A string giving the complete internal subset from the document.
   This does not include the brackets which enclose the subset.  If
   the document has no internal subset, this should be "None".

DocumentType.name

   The name of the root element as given in the "DOCTYPE" declaration,
   if present.

DocumentType.entities

   This is a "NamedNodeMap" of "Entity" nodes giving the definitions
   of external entities. For entity names defined more than once, only
   the first definition is provided (others are ignored as required by
   the XML recommendation).  This may be "None" if the information is
   not provided by the parser, or if no entities are defined.

DocumentType.notations

   This is a "NamedNodeMap" of "Notation" nodes giving the definitions
   of notations. For notation names defined more than once, only the
   first definition is provided (others are ignored as required by the
   XML recommendation).  This may be "None" if the information is not
   provided by the parser, or if no notations are defined.


Document Objects
----------------

A "Document" represents an entire XML document, including its
constituent elements, attributes, processing instructions, comments
etc.  Remember that it inherits properties from "Node".

Document.documentElement

   The one and only root element of the document.

Document.doctype

   The "DocumentType" node of the document, or "None". This is a read-
   only attribute.

Document.implementation

   The "DOMImplementation" object which created this document. This is
   a read-only attribute.

Document.strictErrorChecking

   Whether error checking is enforced.

Document.documentURI

   The location of the document, or "None" if it is unknown.

Document.createDocumentFragment()

   Create and return an empty "DocumentFragment" node.

Document.createCDATASection(data)

   Create and return a "CDATASection" node containing *data*.

Document.importNode(importedNode, deep)

   Return a copy of *importedNode* which belongs to this document. The
   original node is not removed from its document. If *deep* is true,
   the descendants of the node are copied too.

Document.createElement(tagName)

   Create and return a new element node.  The element is not inserted
   into the document when it is created.  You need to explicitly
   insert it with one of the other methods such as "insertBefore()" or
   "appendChild()".

Document.createElementNS(namespaceURI, tagName)

   Create and return a new element with a namespace.  The *tagName*
   may have a prefix.  The element is not inserted into the document
   when it is created.  You need to explicitly insert it with one of
   the other methods such as "insertBefore()" or "appendChild()".

Document.createTextNode(data)

   Create and return a text node containing the data passed as a
   parameter.  As with the other creation methods, this one does not
   insert the node into the tree.

Document.createComment(data)

   Create and return a comment node containing the data passed as a
   parameter.  As with the other creation methods, this one does not
   insert the node into the tree.

Document.createProcessingInstruction(target, data)

   Create and return a processing instruction node containing the
   *target* and *data* passed as parameters.  As with the other
   creation methods, this one does not insert the node into the tree.

Document.createAttribute(name)

   Create and return an attribute node.  This method does not
   associate the attribute node with any particular element.  You must
   use "setAttributeNode()" on the appropriate "Element" object to use
   the newly created attribute instance.

Document.createAttributeNS(namespaceURI, qualifiedName)

   Create and return an attribute node with a namespace.  The
   *tagName* may have a prefix.  This method does not associate the
   attribute node with any particular element.  You must use
   "setAttributeNode()" on the appropriate "Element" object to use the
   newly created attribute instance.

Document.getElementById(id)

   Return the element with the given ID, or "None". Only attributes
   declared as being of type ID in the DTD or by
   "Element.setIdAttribute()" are searched.

Document.getElementsByTagName(tagName)

   Search for all descendants (direct children, children’s children,
   etc.) with a particular element type name.

Document.getElementsByTagNameNS(namespaceURI, localName)

   Search for all descendants (direct children, children’s children,
   etc.) with a particular namespace URI and localname.  The localname
   is the part of the namespace after the prefix.

Document.renameNode(n, namespaceURI, name)

   Rename the element or attribute node *n* and return it.
   *namespaceURI* is the new namespace URI, or "EMPTY_NAMESPACE" if
   the node does not belong to a namespace. *name* is the new
   qualified name.

   Raise "WrongDocumentErr" if *n* was created by another document,
   and "NotSupportedErr" if it is neither an element nor an attribute.


Element Objects
---------------

"Element" is a subclass of "Node", so inherits all the attributes of
that class.

Element.tagName

   The element type name.  In a namespace-using document it may have
   colons in it. The value is a string.

Element.setIdAttribute(name)

   Declare that the attribute *name* is of type ID, so that the
   element is found by "Document.getElementById()". Raise
   "NotFoundErr" if the element has no such attribute.

Element.setIdAttributeNS(namespaceURI, localName)

   The same as "setIdAttribute()", but for an attribute specified by
   its namespace URI and local name.

Element.setIdAttributeNode(idAttr)

   The same as "setIdAttribute()", but for an already retrieved
   attribute node.

Element.getElementsByTagName(tagName)

   Same as equivalent method in the "Document" class.

Element.getElementsByTagNameNS(namespaceURI, localName)

   Same as equivalent method in the "Document" class.

Element.hasAttribute(name)

   Return "True" if the element has an attribute named by *name*.

Element.hasAttributeNS(namespaceURI, localName)

   Return "True" if the element has an attribute named by
   *namespaceURI* and *localName*.

Element.getAttribute(name)

   Return the value of the attribute named by *name* as a string. If
   no such attribute exists, an empty string is returned, as if the
   attribute had no value.

Element.getAttributeNode(attrname)

   Return the "Attr" node for the attribute named by *attrname*.

Element.getAttributeNS(namespaceURI, localName)

   Return the value of the attribute named by *namespaceURI* and
   *localName* as a string. If no such attribute exists, an empty
   string is returned, as if the attribute had no value.

Element.getAttributeNodeNS(namespaceURI, localName)

   Return an attribute value as a node, given a *namespaceURI* and
   *localName*.

Element.removeAttribute(name)

   Remove an attribute by name.

Element.removeAttributeNode(oldAttr)

   Remove and return *oldAttr* from the attribute list, if present. If
   *oldAttr* is not present, "NotFoundErr" is raised.

Element.removeAttributeNS(namespaceURI, localName)

   Remove an attribute by name.  Note that it uses a localName, not a
   qname.

Element.setAttribute(name, value)

   Set an attribute value from a string.

Element.setAttributeNode(newAttr)

   Add a new attribute node to the element, replacing an existing
   attribute if necessary if the "name" attribute matches.  If a
   replacement occurs, the old attribute node will be returned.  If
   *newAttr* is already in use, "InuseAttributeErr" will be raised.

Element.setAttributeNodeNS(newAttr)

   Add a new attribute node to the element, replacing an existing
   attribute if necessary if the "namespaceURI" and "localName"
   attributes match.  If a replacement occurs, the old attribute node
   will be returned.  If *newAttr* is already in use,
   "InuseAttributeErr" will be raised.

Element.setAttributeNS(namespaceURI, qname, value)

   Set an attribute value from a string, given a *namespaceURI* and a
   *qname*. Note that a qname is the whole attribute name.  This is
   different than above.


Attr Objects
------------

"Attr" inherits from "Node", so inherits all its attributes.

Attribute nodes are not part of the document tree. They are contained
in the "attributes" map of an element, not in its children, and their
"parentNode", "previousSibling" and "nextSibling" are always "None".

Attr.name

   The attribute name. In a namespace-using document it may include a
   colon.

Attr.localName

   The part of the name following the colon if there is one, else the
   entire name. This is a read-only attribute.

Attr.prefix

   The part of the name preceding the colon if there is one, else the
   empty string.

Attr.isId

   Whether this attribute is of type ID, either because it is declared
   as such in the DTD or because "Element.setIdAttribute()" was used.
   This is a read-only attribute.

Attr.ownerElement

   The "Element" node to which this attribute belongs, or "None" if it
   is not used. This is a read-only attribute.

Attr.specified

   Whether the value of the attribute was explicitly set in the
   document, as opposed to being defaulted from the DTD. This is a
   read-only attribute.

Attr.value

   The text value of the attribute.  This is a synonym for the
   "nodeValue" attribute.


NamedNodeMap Objects
--------------------

"NamedNodeMap" does *not* inherit from "Node".

NamedNodeMap.length

   The length of the attribute list.

NamedNodeMap.item(index)

   Return an attribute with a particular index.  The order you get the
   attributes in is arbitrary but will be consistent for the life of a
   DOM.  Each item is an attribute node.  Get its value with the
   "value" attribute.

NamedNodeMap.getNamedItem(name)

   Return the node with the given "name", or "None" if there is no
   such node.

NamedNodeMap.getNamedItemNS(namespaceURI, localName)

   Return the node with the given namespace URI and local name, or
   "None" if there is no such node.

NamedNodeMap.setNamedItem(node)

   Add *node* to the map, using its "name" as the key. Return the node
   which it replaces, or "None" if it replaces no node.

NamedNodeMap.setNamedItemNS(node)

   Add *node* to the map, using its namespace URI and local name as
   the key. Return the node which it replaces, or "None" if it
   replaces no node.

NamedNodeMap.removeNamedItem(name)

   Remove and return the node with the given "name". Raise
   "NotFoundErr" if there is no such node.

NamedNodeMap.removeNamedItemNS(namespaceURI, localName)

   Remove and return the node with the given namespace URI and local
   name. Raise "NotFoundErr" if there is no such node.

You can also use the standardized "getAttribute*()" family of methods
on the "Element" objects.


DocumentFragment Objects
------------------------

"DocumentFragment" is a lightweight container of nodes. It is a
subclass of "Node". When it is inserted into the document tree, its
children are inserted instead of it, and it becomes empty.


CharacterData Objects
---------------------

"CharacterData" represents text-like data in the XML document. It is a
subclass of "Node", and the base class of "Text", "CDATASection" and
"Comment". Such nodes cannot have child nodes.

CharacterData.data

   The content of the node as a string.

CharacterData.length

   The number of characters in "data". This is a read-only attribute.

CharacterData.substringData(offset, count)

   Return the substring of "data" of *count* characters starting at
   *offset*.

CharacterData.appendData(arg)

   Append the string *arg* to "data".

CharacterData.insertData(offset, arg)

   Insert the string *arg* into "data" at *offset*.

CharacterData.deleteData(offset, count)

   Remove *count* characters from "data" starting at *offset*.

CharacterData.replaceData(offset, count, arg)

   Replace *count* characters of "data" starting at *offset* with the
   string *arg*.


Comment Objects
---------------

"Comment" represents a comment in the XML document. It is a subclass
of "CharacterData".

Comment.data

   The content of the comment as a string.  The attribute contains all
   characters between the leading "<!-""-" and trailing "-""->", but
   does not include them.


Text and CDATASection Objects
-----------------------------

The "Text" interface represents text in the XML document.  If the
parser and DOM implementation support the DOM’s XML extension,
portions of the text enclosed in CDATA marked sections are stored in
"CDATASection" objects. These two interfaces are identical, but
provide different values for the "nodeType" attribute.

"Text" extends the "CharacterData" interface, and "CDATASection"
extends "Text".

Text.data

   The content of the text node as a string.

Text.wholeText

   The text of all "Text" nodes logically adjacent to this node,
   concatenated in document order. This is a read-only attribute.

Text.replaceWholeText(content)

   Replace the text of all "Text" nodes logically adjacent to this
   node with *content*, removing the other nodes. Return this node, or
   "None" if *content* is empty.

Text.splitText(offset)

   Split this node into two nodes at *offset*, keeping the first part
   in this node and returning a new sibling node with the rest.

Note:

  The use of a "CDATASection" node does not indicate that the node
  represents a complete CDATA marked section, only that the content of
  the node was part of a CDATA section.  A single CDATA section may be
  represented by more than one node in the document tree.  There is no
  way to determine whether two adjacent "CDATASection" nodes represent
  different CDATA marked sections.


ProcessingInstruction Objects
-----------------------------

Represents a processing instruction in the XML document; this inherits
from the "Node" interface and cannot have child nodes.

ProcessingInstruction.target

   The content of the processing instruction up to the first
   whitespace character. This is a read-only attribute.

ProcessingInstruction.data

   The content of the processing instruction following the first
   whitespace character.


Entity Objects
--------------

"Entity" represents a parsed or unparsed entity declared in the DTD.
It is a subclass of "Node". Entity nodes are contained in
"DocumentType.entities" and cannot be inserted into the document tree.
The name of the entity is its "nodeName".

Entity.publicId

   The public identifier of the entity, or "None" if it is not
   specified. This is a read-only attribute.

Entity.systemId

   The system identifier of the entity, or "None" if it is not
   specified. This is a read-only attribute.

Entity.notationName

   The name of the notation for an unparsed entity, or "None" for a
   parsed entity. This is a read-only attribute.


Notation Objects
----------------

"Notation" represents a notation declared in the DTD. It is a subclass
of "Node" and cannot have child nodes. Notation nodes are contained in
"DocumentType.notations" and cannot be inserted into the document
tree. The name of the notation is its "nodeName".

Notation.publicId

   The public identifier of the notation, or "None" if it is not
   specified. This is a read-only attribute.

Notation.systemId

   The system identifier of the notation, or "None" if it is not
   specified. This is a read-only attribute.


Exceptions
----------

The DOM Level 2 recommendation defines a single exception,
"DOMException", and a number of constants that allow applications to
determine what sort of error occurred. "DOMException" instances carry
a "code" attribute that provides the appropriate value for the
specific exception.

The Python DOM interface provides the constants, but also expands the
set of exceptions so that a specific exception exists for each of the
exception codes defined by the DOM.  The implementations must raise
the appropriate specific exception, each of which carries the
appropriate value for the "code" attribute.

exception xml.dom.DOMException

   Base exception class used for all specific DOM exceptions.  This
   exception class cannot be directly instantiated.

exception xml.dom.DomstringSizeErr

   Raised when a specified range of text does not fit into a string.
   This is not known to be used in the Python DOM implementations, but
   may be received from DOM implementations not written in Python.

exception xml.dom.HierarchyRequestErr

   Raised when an attempt is made to insert a node where the node type
   is not allowed.

exception xml.dom.IndexSizeErr

   Raised when an index or size parameter to a method is negative or
   exceeds the allowed values.

exception xml.dom.InuseAttributeErr

   Raised when an attempt is made to insert an "Attr" node that is
   already present elsewhere in the document.

exception xml.dom.InvalidAccessErr

   Raised if a parameter or an operation is not supported on the
   underlying object.

exception xml.dom.InvalidCharacterErr

   This exception is raised when a string parameter contains a
   character that is not permitted in the context it’s being used in
   by the XML 1.0 recommendation. For example, attempting to create an
   "Element" node with a space in the element type name will cause
   this error to be raised.

exception xml.dom.InvalidModificationErr

   Raised when an attempt is made to modify the type of a node.

exception xml.dom.InvalidStateErr

   Raised when an attempt is made to use an object that is not defined
   or is no longer usable.

exception xml.dom.NamespaceErr

   If an attempt is made to change any object in a way that is not
   permitted with regard to the Namespaces in XML recommendation, this
   exception is raised.

exception xml.dom.NotFoundErr

   Exception when a node does not exist in the referenced context.
   For example, "NamedNodeMap.removeNamedItem()" will raise this if
   the node passed in does not exist in the map.

exception xml.dom.NotSupportedErr

   Raised when the implementation does not support the requested type
   of object or operation.

exception xml.dom.NoDataAllowedErr

   This is raised if data is specified for a node which does not
   support data.

exception xml.dom.NoModificationAllowedErr

   Raised on attempts to modify an object where modifications are not
   allowed (such as for read-only nodes).

exception xml.dom.SyntaxErr

   Raised when an invalid or illegal string is specified.

exception xml.dom.ValidationErr

   Raised when an operation would make the document invalid with
   respect to partial validity. This is not known to be used in the
   Python DOM implementations, but may be received from DOM
   implementations not written in Python.

exception xml.dom.WrongDocumentErr

   Raised when a node is inserted in a different document than it
   currently belongs to, and the implementation does not support
   migrating the node from one document to the other.

The exception codes defined in the DOM recommendation map to the
exceptions described above according to this table:

+-----------------------------------------+-----------------------------------+
| Constant                                | Exception                         |
|=========================================|===================================|
| xml.dom.DOMSTRING_SIZE_ERR              | "DomstringSizeErr"                |
+-----------------------------------------+-----------------------------------+
| xml.dom.HIERARCHY_REQUEST_ERR           | "HierarchyRequestErr"             |
+-----------------------------------------+-----------------------------------+
| xml.dom.INDEX_SIZE_ERR                  | "IndexSizeErr"                    |
+-----------------------------------------+-----------------------------------+
| xml.dom.INUSE_ATTRIBUTE_ERR             | "InuseAttributeErr"               |
+-----------------------------------------+-----------------------------------+
| xml.dom.INVALID_ACCESS_ERR              | "InvalidAccessErr"                |
+-----------------------------------------+-----------------------------------+
| xml.dom.INVALID_CHARACTER_ERR           | "InvalidCharacterErr"             |
+-----------------------------------------+-----------------------------------+
| xml.dom.INVALID_MODIFICATION_ERR        | "InvalidModificationErr"          |
+-----------------------------------------+-----------------------------------+
| xml.dom.INVALID_STATE_ERR               | "InvalidStateErr"                 |
+-----------------------------------------+-----------------------------------+
| xml.dom.NAMESPACE_ERR                   | "NamespaceErr"                    |
+-----------------------------------------+-----------------------------------+
| xml.dom.NOT_FOUND_ERR                   | "NotFoundErr"                     |
+-----------------------------------------+-----------------------------------+
| xml.dom.NOT_SUPPORTED_ERR               | "NotSupportedErr"                 |
+-----------------------------------------+-----------------------------------+
| xml.dom.NO_DATA_ALLOWED_ERR             | "NoDataAllowedErr"                |
+-----------------------------------------+-----------------------------------+
| xml.dom.NO_MODIFICATION_ALLOWED_ERR     | "NoModificationAllowedErr"        |
+-----------------------------------------+-----------------------------------+
| xml.dom.SYNTAX_ERR                      | "SyntaxErr"                       |
+-----------------------------------------+-----------------------------------+
| xml.dom.VALIDATION_ERR                  | "ValidationErr"                   |
+-----------------------------------------+-----------------------------------+
| xml.dom.WRONG_DOCUMENT_ERR              | "WrongDocumentErr"                |
+-----------------------------------------+-----------------------------------+


Conformance
===========

This section describes the conformance requirements and relationships
between the Python DOM API, the W3C DOM recommendations, and the OMG
IDL mapping for Python.


Type Mapping
------------

The IDL types used in the DOM specification are mapped to Python types
according to the following table.

+--------------------+---------------------------------------------+
| IDL Type           | Python Type                                 |
|====================|=============================================|
| "boolean"          | "bool" or "int"                             |
+--------------------+---------------------------------------------+
| "int"              | "int"                                       |
+--------------------+---------------------------------------------+
| "long int"         | "int"                                       |
+--------------------+---------------------------------------------+
| "unsigned int"     | "int"                                       |
+--------------------+---------------------------------------------+
| "DOMString"        | "str" or "bytes"                            |
+--------------------+---------------------------------------------+
| "null"             | "None"                                      |
+--------------------+---------------------------------------------+


Accessor Methods
----------------

The mapping from OMG IDL to Python defines accessor functions for IDL
"attribute" declarations in much the way the Java mapping does.
Mapping the IDL declarations

   readonly attribute string someValue;
            attribute string anotherValue;

yields three accessor functions:  a “get” method for "someValue"
("_get_someValue()"), and “get” and “set” methods for "anotherValue"
("_get_anotherValue()" and "_set_anotherValue()").  The mapping, in
particular, does not require that the IDL attributes are accessible as
normal Python attributes:  "object.someValue" is *not* required to
work, and may raise an "AttributeError".

The Python DOM API, however, *does* require that normal attribute
access work. This means that the typical surrogates generated by
Python IDL compilers are not likely to work, and wrapper objects may
be needed on the client if the DOM objects are accessed via CORBA.
While this does require some additional consideration for CORBA DOM
clients, the implementers with experience using DOM over CORBA from
Python do not consider this a problem.  Attributes that are declared
"readonly" may not restrict write access in all DOM implementations.

In the Python DOM API, accessor functions are not required.  If
provided, they should take the form defined by the Python IDL mapping,
but these methods are considered unnecessary since the attributes are
accessible directly from Python. “Set” accessors should never be
provided for "readonly" attributes.

The IDL definitions do not fully embody the requirements of the W3C
DOM API, such as the notion of certain objects, such as the return
value of "getElementsByTagName()", being “live”.  The Python DOM API
does not require implementations to enforce such requirements.
