Document Object Model (Core) Level 1

REC-DOM-Level-1-19981001

# 1. Document Object Model (Core) Level 1

Editors
  Mike Champion, ArborText (from November 20, 1997)
  Steve Byrne, JavaSoft (until November 19, 1997)
  Gavin Nicol, Inso EPS
  Lauren Wood, SoftQuad, Inc.

## Table of contents

## 1.1. Overview of the DOM Core Interfaces

This section defines a minimal set of objects and interfaces for accessing and manipulating document objects. The functionality specified in this section (the Core functionality) should be sufficient to allow software developers and web script authors to access and manipulate parsed HTML and XML content inside conforming products. The DOM Core API also allows population of a `Document` object using only DOM API calls; creating the skeleton `Document` and saving it persistently is left to the product that implements the DOM API.

### 1.1.1. The DOM Structure Model

The DOM presents documents as a hierarchy of `Node` objects that also implement other, more specialized interfaces. Some types of nodes may have child nodes of various types, and others are leaf nodes that cannot have anything below them in the document structure. The node types, and which node types they may have as children, are as follows:

- `Document` -- `Element` (maximum of one), `ProcessingInstruction`, `Comment`, `DocumentType`
- `DocumentFragment` -- `Element`, `ProcessingInstruction`, `Comment`, `Text`, `CDATASection`, `EntityReference`
- `DocumentType` -- no children
- `EntityReference` -- `Element`, `ProcessingInstruction`, `Comment`, `Text`, `CDATASection`, `EntityReference`
- `Element` -- `Element`, `Text`, `Comment`, `ProcessingInstruction`, `CDATASection`, `EntityReference`
- `Attr` -- `Text`, `EntityReference`
- `ProcessingInstruction` -- no children
- `Comment` -- no children
- `Text` -- no children
- `CDATASection` -- no children
- `Entity` -- `Element`, `ProcessingInstruction`, `Comment`, `Text`, `CDATASection`, `EntityReference`
- `Notation` -- no children

The DOM also specifies a `NodeList` interface to handle ordered lists of `Node`s, such as the children of a `Node`, or the elements returned by the `Element.getElementsByTagName` method, and also a `NamedNodeMap` interface to handle unordered sets of nodes referenced by their name attribute, such as the attributes of an `Element`. `NodeList`s and `NamedNodeMap`s in the DOM are "live", that is, changes to the underlying document structure are reflected in all relevant `NodeList`s and `NamedNodeMap`s. For example, if a DOM user gets a `NodeList` object containing the children of an `Element`, then subsequently adds more children to that element (or removes children, or modifies them), those changes are automatically reflected in the `NodeList` without further action on the user's part. Likewise changes to a `Node` in the tree are reflected in all references to that `Node` in `NodeList`s and `NamedNodeMap`s.

### 1.1.2. Memory Management

Most of the APIs defined by this specification are interfaces rather than classes. That means that an actual implementation need only expose methods with the defined names and specified operation, not actually implement classes that correspond directly to the interfaces. This allows the DOM APIs to be implemented as a thin veneer on top of legacy applications with their own data structures, or on top of newer applications with different class hierarchies. This also means that ordinary constructors (in the Java or C++ sense) cannot be used to create DOM objects, since the underlying objects to be constructed may have little relationship to the DOM interfaces. The conventional solution to this in object-oriented design is to define factory methods that create instances of objects that implement the various interfaces. In the DOM Level 1, objects implementing some interface "X" are created by a "createX()" method on the `Document` interface; this is because all DOM objects live in the context of a specific Document.

The DOM Level 1 API does not define a standard way to create `DOMImplementation` or `Document` objects; actual DOM implementations must provide some proprietary way of bootstrapping these DOM interfaces, and then all other objects can be built from the Create methods on `Document` (or by various other convenience methods).

The Core DOM APIs are designed to be compatible with a wide range of languages, including both general-user scripting languages and the more challenging languages used mostly by professional programmers. Thus, the DOM APIs need to operate across a variety of memory management philosophies, from language platforms that do not expose memory management to the user at all, through those (notably Java) that provide explicit constructors but provide an automatic garbage collection mechanism to automatically reclaim unused memory, to those (especially C/C++) that generally require the programmer to explicitly allocate object memory, track where it is used, and explicitly free it for re-use. To ensure a consistent API across these platforms, the DOM does not address memory management issues at all, but instead leaves these for the implementation. Neither of the explicit language bindings devised by the DOM Working Group (for ECMAScript and Java) require any memory management methods, but DOM bindings for other languages (especially C or C++) probably will require such support. These extensions will be the responsibility of those adapting the DOM API to a specific language, not the DOM WG.

### 1.1.3. Naming Conventions

While it would be nice to have attribute and method names that are short, informative, internally consistent, and familiar to users of similar APIs, the names also should not clash with the names in legacy APIs supported by DOM implementations. Furthermore, both OMG IDL and `ECMAScript` have significant limitations in their ability to disambiguate names from different namespaces that makes it difficult to avoid naming conflicts with short, familiar names. So, DOM names tend to be long and quite descriptive in order to be unique across all environments.

The Working Group has also attempted to be internally consistent in its use of various terms, even though these may not be common distinctions in other APIs. For example, we use the method name "remove" when the method changes the structural model, and the method name "delete" when the method gets rid of something inside the structure model. The thing that is deleted is not returned. The thing that is removed may be returned, when it makes sense to return it.

### 1.1.4. Inheritance vs Flattened Views of the API

The DOM Core APIs present two somewhat different sets of interfaces to an XML/HTML document; one presenting an "object oriented" approach with a hierarchy of inheritance, and a "simplified" view that allows all manipulation to be done via the `Node` interface without requiring casts (in Java and other C-like languages) or query interface calls in COM environments. These operations are fairly expensive in Java and COM, and the DOM may be used in performance-critical environments, so we allow significant functionality using just the `Node` interface. Because many other users will find the inheritance hierarchy easier to understand than the "everything is a `Node`" approach to the DOM, we also support the full higher-level interfaces for those who prefer a more object-oriented API.

In practice, this means that there is a certain amount of redundancy in the API. The Working Group considers the "inheritance" approach the primary view of the API, and the full set of functionality on `Node` to be "extra" functionality that users may employ, but that does not eliminate the need for methods on other interfaces that an object-oriented analysis would dictate. (Of course, when the O-O analysis yields an attribute or method that is identical to one on the `Node` interface, we don't specify a completely redundant one). Thus, even though there is a generic `nodeName` attribute on the `Node` interface, there is still a `tagName` attribute on the `Element` interface; these two attributes must contain the same value, but the Working Group considers it worthwhile to support both, given the different constituencies the DOM API must satisfy.

### 1.1.5. The `DOMString` type

To ensure interoperability, the DOM specifies the `DOMString` type as follows:

- A `DOMString` is a sequence of 16-bit quantities. This may be expressed in IDL terms as:

               typedef sequence<unsigned short> DOMString;

- Applications must encode `DOMString` using UTF-16 (defined in Appendix C.3 of [UNICODE] and Amendment 1 of [ISO-10646]).The UTF-16 encoding was chosen because of its widespread industry practice. Please note that for both HTML and XML, the document character set (and therefore the notation of numeric character references) is based on UCS-4. A single numeric character reference in a source document may therefore in some cases correspond to two array positions in a `DOMString` (a high surrogate and a low surrogate). Note: Even though the DOM defines the name of the string type to be `DOMString`, bindings may used different names. For, example for Java, `DOMString` is bound to the `String` type because it also uses UTF-16 as its encoding.

Note: As of August 1998, the OMG IDL specification included a `wstring` type. However, that definition did not meet the interoperability criteria of the DOM API since it relied on encoding negotiation to decide the width of a character.

### 1.1.6. Case sensitivity in the DOM

The DOM has many interfaces that imply string matching. HTML processors generally assume an uppercase (less often, lowercase) normalization of names for such things as elements, while XML is explicitly case sensitive. For the purposes of the DOM, string matching takes place on a character code by character code basis, on the 16 bit value of a `DOMString`. As such, the DOM assumes that any normalizations will take place in the processor, before the DOM structures are built.

This then raises the issue of exactly what normalizations occur. The W3C I18N working group is in the process of defining exactly which normalizations are necessary for applications implementing the DOM.

## 1.2. Fundamental Interfaces

The interfaces within this section are considered fundamental, and must be fully implemented by all conforming implementations of the DOM, including all HTML DOM implementations.

Exception DOMException

  DOM operations only raise exceptions in "exceptional" circumstances, i.e., when an operation is impossible to perform (either for logical reasons, because data is lost, or because the implementation has become unstable). In general, DOM methods return specific error values in ordinary processing situation, such as out-of-bound errors when using `NodeList`.

  Implementations may raise other exceptions under other circumstances. For example, implementations may raise an implementation-dependent exception if a `null` argument is passed.

  Some languages and object systems do not support the concept of exceptions. For such systems, error conditions may be indicated using native error reporting mechanisms. For some bindings, for example, methods may return error codes similar to those listed in the corresponding method descriptions.

  IDL Definition

        exception DOMException {
          unsigned short   code;
        };

        // ExceptionCode
        const unsigned short      INDEX_SIZE_ERR     = 1;
        const unsigned short      DOMSTRING_SIZE_ERR = 2;
        const unsigned short      HIERARCHY_REQUEST_ERR = 3;
        const unsigned short      WRONG_DOCUMENT_ERR = 4;
        const unsigned short      INVALID_CHARACTER_ERR = 5;
        const unsigned short      NO_DATA_ALLOWED_ERR = 6;
        const unsigned short      NO_MODIFICATION_ALLOWED_ERR = 7;
        const unsigned short      NOT_FOUND_ERR      = 8;
        const unsigned short      NOT_SUPPORTED_ERR  = 9;
        const unsigned short      INUSE_ATTRIBUTE_ERR = 10;

  Definition group ExceptionCode

    An integer indicating the type of error generated.

    Defined Constants

      INDEX_SIZE_ERR | If index or size is negative, or greater than the allowed value
      DOMSTRING_SIZE_ERR | If the specified range of text does not fit into a DOMString
      HIERARCHY_REQUEST_ERR | If any node is inserted somewhere it doesn't belong
      WRONG_DOCUMENT_ERR | If a node is used in a different document than the one that created it (that doesn't support it)
      INVALID_CHARACTER_ERR | If an invalid character is specified, such as in a name.
      NO_DATA_ALLOWED_ERR | If data is specified for a node which does not support data
      NO_MODIFICATION_ALLOWED_ERR | If an attempt is made to modify an object where modifications are not allowed
      NOT_FOUND_ERR | If an attempt was made to reference a node in a context where it does not exist
      NOT_SUPPORTED_ERR | If the implementation does not support the type of object requested
      INUSE_ATTRIBUTE_ERR | If an attempt is made to add an attribute that is already inuse elsewhere

Interface DOMImplementation

  The `DOMImplementation` interface provides a number of methods for performing operations that are independent of any particular instance of the document object model.

  The DOM Level 1 does not specify a way of creating a document instance, and hence document creation is an operation specific to an implementation. Future Levels of the DOM specification are expected to provide methods for creating documents directly.

  IDL Definition

        interface DOMImplementation {
          boolean                   hasFeature(in DOMString feature,
                                               in DOMString version);
        };

  Methods
    `hasFeature`
      Test if the DOM implementation implements a specific feature.
      Parameters

        `feature` |  | The package name of the feature to test. In Level 1, the legal values are "HTML" and "XML" (case-insensitive).
        `version` |  | This is the version number of the package name to test. In Level 1, this is the string "1.0". If the version is not specified, supporting any version of the feature will cause the method to return `true`.

      Return Value
        `true` if the feature is implemented in the specified version, `false` otherwise.
      This method raises no exceptions.

Interface DocumentFragment

  `DocumentFragment` is a "lightweight" or "minimal" `Document` object. It is very common to want to be able to extract a portion of a document's tree or to create a new fragment of a document. Imagine implementing a user command like cut or rearranging a document by moving fragments around. It is desirable to have an object which can hold such fragments and it is quite natural to use a Node for this purpose. While it is true that a `Document` object could fulfil this role, a `Document` object can potentially be a heavyweight object, depending on the underlying implementation. What is really needed for this is a very lightweight object. `DocumentFragment` is such an object.

  Furthermore, various operations -- such as inserting nodes as children of another `Node` -- may take `DocumentFragment` objects as arguments; this results in all the child nodes of the `DocumentFragment` being moved to the child list of this node.

  The children of a `DocumentFragment` node are zero or more nodes representing the tops of any sub-trees defining the structure of the document. `DocumentFragment` nodes do not need to be well-formed XML documents (although they do need to follow the rules imposed upon well-formed XML parsed entities, which can have multiple top nodes). For example, a `DocumentFragment` might have only one child and that child node could be a `Text` node. Such a structure model represents neither an HTML document nor a well-formed XML document.

  When a `DocumentFragment` is inserted into a `Document` (or indeed any other `Node` that may take children) the children of the `DocumentFragment` and not the `DocumentFragment` itself are inserted into the `Node`. This makes the `DocumentFragment` very useful when the user wishes to create nodes that are siblings; the `DocumentFragment` acts as the parent of these nodes so that the user can use the standard methods from the `Node` interface, such as `insertBefore()` and `appendChild()`.

  IDL Definition

        interface DocumentFragment : Node {
        };

Interface Document

  The `Document` interface represents the entire HTML or XML document. Conceptually, it is the root of the document tree, and provides the primary access to the document's data.

  Since elements, text nodes, comments, processing instructions, etc. cannot exist outside the context of a `Document`, the `Document` interface also contains the factory methods needed to create these objects. The `Node` objects created have a `ownerDocument` attribute which associates them with the `Document` within whose context they were created.

  IDL Definition

        interface Document : Node {
          readonly attribute  DocumentType         doctype;
          readonly attribute  DOMImplementation    implementation;
          readonly attribute  Element              documentElement;
          Element                   createElement(in DOMString tagName)
                                                  raises(DOMException);
          DocumentFragment          createDocumentFragment();
          Text                      createTextNode(in DOMString data);
          Comment                   createComment(in DOMString data);
          CDATASection              createCDATASection(in DOMString data)
                                                       raises(DOMException);
          ProcessingInstruction     createProcessingInstruction(in DOMString target,
                                                                in DOMString data)
                                                                raises(DOMException);
          Attr                      createAttribute(in DOMString name)
                                                    raises(DOMException);
          EntityReference           createEntityReference(in DOMString name)
                                                          raises(DOMException);
          NodeList                  getElementsByTagName(in DOMString tagname);
        };

  Attributes
    `doctype`
      The Document Type Declaration (see `DocumentType`) associated with this document. For HTML documents as well as XML documents without a document type declaration this returns `null`. The DOM Level 1 does not support editing the Document Type Declaration, therefore `docType` cannot be altered in any way.
    `implementation`
      The `DOMImplementation` object that handles this document. A DOM application may use objects from multiple implementations.
    `documentElement`
      This is a convenience attribute that allows direct access to the child node that is the root element of the document. For HTML documents, this is the element with the tagName "HTML".
  Methods
    `createElement`
      Creates an element of the type specified. Note that the instance returned implements the Element interface, so attributes can be specified directly on the returned object.
      Parameters

        `tagName` |  | The name of the element type to instantiate. For XML, this is case-sensitive. For HTML, the `tagName` parameter may be provided in any case, but it must be mapped to the canonical uppercase form by the DOM implementation.

      Return Value
        A new `Element` object.
      Exceptions
        `DOMException`

          INVALID_CHARACTER_ERR: Raised if the specified name contains an invalid character.

    `createDocumentFragment`
      Creates an empty `DocumentFragment` object.
      Return Value
        A new `DocumentFragment`.
      This method has no parameters.
      This method raises no exceptions.
    `createTextNode`
      Creates a `Text` node given the specified string.
      Parameters

        `data` |  | The data for the node.

      Return Value
        The new `Text` object.
      This method raises no exceptions.
    `createComment`
      Creates a `Comment` node given the specified string.
      Parameters

        `data` |  | The data for the node.

      Return Value
        The new `Comment` object.
      This method raises no exceptions.
    `createCDATASection`
      Creates a `CDATASection` node whose value is the specified string.
      Parameters

        `data` |  | The data for the `CDATASection` contents.

      Return Value
        The new `CDATASection` object.
      Exceptions
        `DOMException`

          NOT_SUPPORTED_ERR: Raised if this document is an HTML document.

    `createProcessingInstruction`
      Creates a `ProcessingInstruction` node given the specified name and data strings.
      Parameters

        `target` |  | The target part of the processing instruction.
        `data` |  | The data for the node.

      Return Value
        The new `ProcessingInstruction` object.
      Exceptions
        `DOMException`

          INVALID_CHARACTER_ERR: Raised if an invalid character is specified.

          NOT_SUPPORTED_ERR: Raised if this document is an HTML document.

    `createAttribute`
      Creates an `Attr` of the given name. Note that the `Attr` instance can then be set on an `Element` using the `setAttribute` method.
      Parameters

        `name` |  | The name of the attribute.

      Return Value
        A new `Attr` object.
      Exceptions
        `DOMException`

          INVALID_CHARACTER_ERR: Raised if the specified name contains an invalid character.

    `createEntityReference`
      Creates an EntityReference object.
      Parameters

        `name` |  | The name of the entity to reference.

      Return Value
        The new `EntityReference` object.
      Exceptions
        `DOMException`

          INVALID_CHARACTER_ERR: Raised if the specified name contains an invalid character.

          NOT_SUPPORTED_ERR: Raised if this document is an HTML document.

    `getElementsByTagName`
      Returns a `NodeList` of all the `Element`s with a given tag name in the order in which they would be encountered in a preorder traversal of the `Document` tree.
      Parameters

        `tagname` |  | The name of the tag to match on. The special value "*" matches all tags.

      Return Value
        A new `NodeList` object containing all the matched `Element`s.
      This method raises no exceptions.

Interface Node

  The `Node` interface is the primary datatype for the entire Document Object Model. It represents a single node in the document tree. While all objects implementing the `Node` interface expose methods for dealing with children, not all objects implementing the `Node` interface may have children. For example, `Text` nodes may not have children, and adding children to such nodes results in a `DOMException` being raised.

  The attributes `nodeName`, `nodeValue` and `attributes` are included as a mechanism to get at node information without casting down to the specific derived interface. In cases where there is no obvious mapping of these attributes for a specific `nodeType` (e.g., `nodeValue` for an Element or `attributes` for a Comment), this returns `null`. Note that the specialized interfaces may contain additional and more convenient mechanisms to get and set the relevant information.

  IDL Definition

        interface Node {
          // NodeType
          const unsigned short      ELEMENT_NODE       = 1;
          const unsigned short      ATTRIBUTE_NODE     = 2;
          const unsigned short      TEXT_NODE          = 3;
          const unsigned short      CDATA_SECTION_NODE = 4;
          const unsigned short      ENTITY_REFERENCE_NODE = 5;
          const unsigned short      ENTITY_NODE        = 6;
          const unsigned short      PROCESSING_INSTRUCTION_NODE = 7;
          const unsigned short      COMMENT_NODE       = 8;
          const unsigned short      DOCUMENT_NODE      = 9;
          const unsigned short      DOCUMENT_TYPE_NODE = 10;
          const unsigned short      DOCUMENT_FRAGMENT_NODE = 11;
          const unsigned short      NOTATION_NODE      = 12;

          readonly attribute  DOMString            nodeName;
                   attribute  DOMString            nodeValue;
                                                         // raises(DOMException) on setting
                                                         // raises(DOMException) on retrieval
          readonly attribute  unsigned short       nodeType;
          readonly attribute  Node                 parentNode;
          readonly attribute  NodeList             childNodes;
          readonly attribute  Node                 firstChild;
          readonly attribute  Node                 lastChild;
          readonly attribute  Node                 previousSibling;
          readonly attribute  Node                 nextSibling;
          readonly attribute  NamedNodeMap         attributes;
          readonly attribute  Document             ownerDocument;
          Node                      insertBefore(in Node newChild,
                                                 in Node refChild)
                                                 raises(DOMException);
          Node                      replaceChild(in Node newChild,
                                                 in Node oldChild)
                                                 raises(DOMException);
          Node                      removeChild(in Node oldChild)
                                                raises(DOMException);
          Node                      appendChild(in Node newChild)
                                                raises(DOMException);
          boolean                   hasChildNodes();
          Node                      cloneNode(in boolean deep);
        };

  Definition group NodeType

    An integer indicating which type of node this is.

    Defined Constants

      ELEMENT_NODE | The node is a `Element`.
      ATTRIBUTE_NODE | The node is an `Attr`.
      TEXT_NODE | The node is a `Text` node.
      CDATA_SECTION_NODE | The node is a `CDATASection`.
      ENTITY_REFERENCE_NODE | The node is an `EntityReference`.
      ENTITY_NODE | The node is an `Entity`.
      PROCESSING_INSTRUCTION_NODE | The node is a `ProcessingInstruction`.
      COMMENT_NODE | The node is a `Comment`.
      DOCUMENT_NODE | The node is a `Document`.
      DOCUMENT_TYPE_NODE | The node is a `DocumentType`.
      DOCUMENT_FRAGMENT_NODE | The node is a `DocumentFragment`.
      NOTATION_NODE | The node is a `Notation`.

  The values of `nodeName`, `nodeValue`, and `attributes` vary according to the node type as follows:

  | nodeName | nodeValue | attributes
  Element | tagName | null | NamedNodeMap
  Attr | name of attribute | value of attribute | null
  Text | #text | content of the text node | null
  CDATASection | #cdata-section | content of the CDATA Section | null
  EntityReference | name of entity referenced | null | null
  Entity | entity name | null | null
  ProcessingInstruction | target | entire content excluding the target | null
  Comment | #comment | content of the comment | null
  Document | #document | null | null
  DocumentType | document type name | null | null
  DocumentFragment | #document-fragment | null | null
  Notation | notation name | null | null

  Attributes
    `nodeName`
      The name of this node, depending on its type; see the table above.
    `nodeValue`
      The value of this node, depending on its type; see the table above.
      Exceptions on setting
        `DOMException`

          NO_MODIFICATION_ALLOWED_ERR: Raised when the node is readonly.

      Exceptions on retrieval
        `DOMException`

          DOMSTRING_SIZE_ERR: Raised when it would return more characters than fit in a `DOMString` variable on the implementation platform.

    `nodeType`
      A code representing the type of the underlying object, as defined above.
    `parentNode`
      The parent of this node. All nodes, except `Document`, `DocumentFragment`, and `Attr` may have a parent. However, if a node has just been created and not yet added to the tree, or if it has been removed from the tree, this is `null`.
    `childNodes`
      A `NodeList` that contains all children of this node. If there are no children, this is a `NodeList` containing no nodes. The content of the returned `NodeList` is "live" in the sense that, for instance, changes to the children of the node object that it was created from are immediately reflected in the nodes returned by the `NodeList` accessors; it is not a static snapshot of the content of the node. This is true for every `NodeList`, including the ones returned by the `getElementsByTagName` method.
    `firstChild`
      The first child of this node. If there is no such node, this returns `null`.
    `lastChild`
      The last child of this node. If there is no such node, this returns `null`.
    `previousSibling`
      The node immediately preceding this node. If there is no such node, this returns `null`.
    `nextSibling`
      The node immediately following this node. If there is no such node, this returns `null`.
    `attributes`
      A `NamedNodeMap` containing the attributes of this node (if it is an `Element`) or `null` otherwise.
    `ownerDocument`
      The `Document` object associated with this node. This is also the `Document` object used to create new nodes. When this node is a `Document` this is `null`.
  Methods
    `insertBefore`
      Inserts the node `newChild` before the existing child node `refChild`. If `refChild` is `null`, insert `newChild` at the end of the list of children.

      If `newChild` is a `DocumentFragment` object, all of its children are inserted, in the same order, before `refChild`. If the `newChild` is already in the tree, it is first removed.

      Parameters

        `newChild` |  | The node to insert.
        `refChild` |  | The reference node, i.e., the node before which the new node must be inserted.

      Return Value
        The node being inserted.
      Exceptions
        `DOMException`

          HIERARCHY_REQUEST_ERR: Raised if this node is of a type that does not allow children of the type of the `newChild` node, or if the node to insert is one of this node's ancestors.

          WRONG_DOCUMENT_ERR: Raised if `newChild` was created from a different document than the one that created this node.

          NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.

          NOT_FOUND_ERR: Raised if `refChild` is not a child of this node.

    `replaceChild`
      Replaces the child node `oldChild` with `newChild` in the list of children, and returns the `oldChild` node. If the `newChild` is already in the tree, it is first removed.
      Parameters

        `newChild` |  | The new node to put in the child list.
        `oldChild` |  | The node being replaced in the list.

      Return Value
        The node replaced.
      Exceptions
        `DOMException`

          HIERARCHY_REQUEST_ERR: Raised if this node is of a type that does not allow children of the type of the `newChild` node, or it the node to put in is one of this node's ancestors.

          WRONG_DOCUMENT_ERR: Raised if `newChild` was created from a different document than the one that created this node.

          NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.

          NOT_FOUND_ERR: Raised if `oldChild` is not a child of this node.

    `removeChild`
      Removes the child node indicated by `oldChild` from the list of children, and returns it.
      Parameters

        `oldChild` |  | The node being removed.

      Return Value
        The node removed.
      Exceptions
        `DOMException`

          NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.

          NOT_FOUND_ERR: Raised if `oldChild` is not a child of this node.

    `appendChild`
      Adds the node `newChild` to the end of the list of children of this node. If the `newChild` is already in the tree, it is first removed.
      Parameters

        `newChild` |  | The node to add. If it is a `DocumentFragment` object, the entire contents of the document fragment are moved into the child list of this node

      Return Value
        The node added.
      Exceptions
        `DOMException`

          HIERARCHY_REQUEST_ERR: Raised if this node is of a type that does not allow children of the type of the `newChild` node, or if the node to append is one of this node's ancestors.

          WRONG_DOCUMENT_ERR: Raised if `newChild` was created from a different document than the one that created this node.

          NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.

    `hasChildNodes`
      This is a convenience method to allow easy determination of whether a node has any children.
      Return Value
        `true` if the node has any children, `false` if the node has no children.
      This method has no parameters.
      This method raises no exceptions.
    `cloneNode`
      Returns a duplicate of this node, i.e., serves as a generic copy constructor for nodes. The duplicate node has no parent (`parentNode` returns `null`.).

      Cloning an `Element` copies all attributes and their values, including those generated by the XML processor to represent defaulted attributes, but this method does not copy any text it contains unless it is a deep clone, since the text is contained in a child `Text` node. Cloning any other type of node simply returns a copy of this node.

      Parameters

        `deep` |  | If `true`, recursively clone the subtree under the specified node; if `false`, clone only the node itself (and its attributes, if it is an `Element`).

      Return Value
        The duplicate node.
      This method raises no exceptions.

Interface NodeList

  The `NodeList` interface provides the abstraction of an ordered collection of nodes, without defining or constraining how this collection is implemented.

  The items in the `NodeList` are accessible via an integral index, starting from 0.

  IDL Definition

        interface NodeList {
          Node                      item(in unsigned long index);
          readonly attribute  unsigned long        length;
        };

  Methods
    `item`
      Returns the `index`th item in the collection. If `index` is greater than or equal to the number of nodes in the list, this returns `null`.
      Parameters

        `index` |  | Index into the collection.

      Return Value
        The node at the `index`th position in the `NodeList`, or `null` if that is not a valid index.
      This method raises no exceptions.
  Attributes
    `length`
      The number of nodes in the list. The range of valid child node indices is 0 to `length-1` inclusive.

Interface NamedNodeMap

  Objects implementing the `NamedNodeMap` interface are used to represent collections of nodes that can be accessed by name. Note that `NamedNodeMap` does not inherit from `NodeList`; `NamedNodeMap`s are not maintained in any particular order. Objects contained in an object implementing `NamedNodeMap` may also be accessed by an ordinal index, but this is simply to allow convenient enumeration of the contents of a `NamedNodeMap`, and does not imply that the DOM specifies an order to these Nodes.

  IDL Definition

        interface NamedNodeMap {
          Node                      getNamedItem(in DOMString name);
          Node                      setNamedItem(in Node arg)
                                                 raises(DOMException);
          Node                      removeNamedItem(in DOMString name)
                                                    raises(DOMException);
          Node                      item(in unsigned long index);
          readonly attribute  unsigned long        length;
        };

  Methods
    `getNamedItem`
      Retrieves a node specified by name.
      Parameters

        `name` |  | Name of a node to retrieve.

      Return Value
        A `Node` (of any type) with the specified name, or `null` if the specified name did not identify any node in the map.
      This method raises no exceptions.
    `setNamedItem`
      Adds a node using its `nodeName` attribute.

      As the `nodeName` attribute is used to derive the name which the node must be stored under, multiple nodes of certain types (those that have a "special" string value) cannot be stored as the names would clash. This is seen as preferable to allowing nodes to be aliased.

      Parameters

        `arg` |  | A node to store in a named node map. The node will later be accessible using the value of the `nodeName` attribute of the node. If a node with that name is already present in the map, it is replaced by the new one.

      Return Value
        If the new `Node` replaces an existing node with the same name the previously existing `Node` is returned, otherwise `null` is returned.
      Exceptions
        `DOMException`

          WRONG_DOCUMENT_ERR: Raised if `arg` was created from a different document than the one that created the `NamedNodeMap`.

          NO_MODIFICATION_ALLOWED_ERR: Raised if this `NamedNodeMap` is readonly.

          INUSE_ATTRIBUTE_ERR: Raised if `arg` is an `Attr` that is already an attribute of another `Element` object. The DOM user must explicitly clone `Attr` nodes to re-use them in other elements.

    `removeNamedItem`
      Removes a node specified by name. If the removed node is an `Attr` with a default value it is immediately replaced.
      Parameters

        `name` |  | The name of a node to remove.

      Return Value
        The node removed from the map or `null` if no node with such a name exists.
      Exceptions
        `DOMException`

          NOT_FOUND_ERR: Raised if there is no node named `name` in the map.

    `item`
      Returns the `index`th item in the map. If `index` is greater than or equal to the number of nodes in the map, this returns `null`.
      Parameters

        `index` |  | Index into the map.

      Return Value
        The node at the `index`th position in the `NamedNodeMap`, or `null` if that is not a valid index.
      This method raises no exceptions.
  Attributes
    `length`
      The number of nodes in the map. The range of valid child node indices is 0 to `length-1` inclusive.

Interface CharacterData

  The `CharacterData` interface extends Node with a set of attributes and methods for accessing character data in the DOM. For clarity this set is defined here rather than on each object that uses these attributes and methods. No DOM objects correspond directly to `CharacterData`, though `Text` and others do inherit the interface from it. All `offset`s in this interface start from 0.

  IDL Definition

        interface CharacterData : Node {
                   attribute  DOMString            data;
                                         // raises(DOMException) on setting
                                         // raises(DOMException) on retrieval
          readonly attribute  unsigned long        length;
          DOMString                 substringData(in unsigned long offset,
                                                  in unsigned long count)
                                                  raises(DOMException);
          void                      appendData(in DOMString arg)
                                               raises(DOMException);
          void                      insertData(in unsigned long offset,
                                               in DOMString arg)
                                               raises(DOMException);
          void                      deleteData(in unsigned long offset,
                                               in unsigned long count)
                                               raises(DOMException);
          void                      replaceData(in unsigned long offset,
                                                in unsigned long count,
                                                in DOMString arg)
                                                raises(DOMException);
        };

  Attributes
    `data`
      The character data of the node that implements this interface. The DOM implementation may not put arbitrary limits on the amount of data that may be stored in a `CharacterData` node. However, implementation limits may mean that the entirety of a node's data may not fit into a single `DOMString`. In such cases, the user may call `substringData` to retrieve the data in appropriately sized pieces.
      Exceptions on setting
        `DOMException`

          NO_MODIFICATION_ALLOWED_ERR: Raised when the node is readonly.

      Exceptions on retrieval
        `DOMException`

          DOMSTRING_SIZE_ERR: Raised when it would return more characters than fit in a `DOMString` variable on the implementation platform.

    `length`
      The number of characters that are available through `data` and the `substringData` method below. This may have the value zero, i.e., `CharacterData` nodes may be empty.
  Methods
    `substringData`
      Extracts a range of data from the node.
      Parameters

        `offset` |  | Start offset of substring to extract.
        `count` |  | The number of characters to extract.

      Return Value
        The specified substring. If the sum of `offset` and `count` exceeds the `length`, then all characters to the end of the data are returned.
      Exceptions
        `DOMException`

          INDEX_SIZE_ERR: Raised if the specified offset is negative or greater than the number of characters in `data`, or if the specified `count` is negative.

          DOMSTRING_SIZE_ERR: Raised if the specified range of text does not fit into a `DOMString`.

    `appendData`
      Append the string to the end of the character data of the node. Upon success, `data` provides access to the concatenation of `data` and the `DOMString` specified.
      Parameters

        `arg` |  | The `DOMString` to append.

      Exceptions
        `DOMException`

          NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.

      This method returns nothing.
    `insertData`
      Insert a string at the specified character offset.
      Parameters

        `offset` |  | The character offset at which to insert.
        `arg` |  | The `DOMString` to insert.

      Exceptions
        `DOMException`

          INDEX_SIZE_ERR: Raised if the specified offset is negative or greater than the number of characters in `data`.

          NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.

      This method returns nothing.
    `deleteData`
      Remove a range of characters from the node. Upon success, `data` and `length` reflect the change.
      Parameters

        `offset` |  | The offset from which to remove characters.
        `count` |  | The number of characters to delete. If the sum of `offset` and `count` exceeds `length` then all characters from `offset` to the end of the data are deleted.

      Exceptions
        `DOMException`

          INDEX_SIZE_ERR: Raised if the specified offset is negative or greater than the number of characters in `data`, or if the specified `count` is negative.

          NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.

      This method returns nothing.
    `replaceData`
      Replace the characters starting at the specified character offset with the specified string.
      Parameters

        `offset` |  | The offset from which to start replacing.
        `count` |  | The number of characters to replace. If the sum of `offset` and `count` exceeds `length`, then all characters to the end of the data are replaced (i.e., the effect is the same as a `remove` method call with the same range, followed by an `append` method invocation).
        `arg` |  | The `DOMString` with which the range must be replaced.

      Exceptions
        `DOMException`

          INDEX_SIZE_ERR: Raised if the specified offset is negative or greater than the number of characters in `data`, or if the specified `count` is negative.

          NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.

      This method returns nothing.

Interface Attr

  The `Attr` interface represents an attribute in an `Element` object. Typically the allowable values for the attribute are defined in a document type definition.

  `Attr` objects inherit the `Node` interface, but since they are not actually child nodes of the element they describe, the DOM does not consider them part of the document tree. Thus, the `Node` attributes `parentNode`, `previousSibling`, and `nextSibling` have a null value for `Attr` objects. The DOM takes the view that attributes are properties of elements rather than having a separate identity from the elements they are associated with; this should make it more efficient to implement such features as default attributes associated with all elements of a given type. Furthermore, `Attr` nodes may not be immediate children of a `DocumentFragment`. However, they can be associated with `Element` nodes contained within a `DocumentFragment`. In short, users and implementors of the DOM need to be aware that `Attr` nodes have some things in common with other objects inheriting the `Node` interface, but they also are quite distinct.

  The attribute's effective value is determined as follows: if this attribute has been explicitly assigned any value, that value is the attribute's effective value; otherwise, if there is a declaration for this attribute, and that declaration includes a default value, then that default value is the attribute's effective value; otherwise, the attribute does not exist on this element in the structure model until it has been explicitly added. Note that the `nodeValue` attribute on the `Attr` instance can also be used to retrieve the string version of the attribute's value(s).

  In XML, where the value of an attribute can contain entity references, the child nodes of the `Attr` node provide a representation in which entity references are not expanded. These child nodes may be either `Text` or `EntityReference` nodes. Because the attribute type may be unknown, there are no tokenized attribute values.

  IDL Definition

        interface Attr : Node {
          readonly attribute  DOMString            name;
          readonly attribute  boolean              specified;
                   attribute  DOMString            value;
        };

  Attributes
    `name`
      Returns the name of this attribute.
    `specified`
      If this attribute was explicitly given a value in the original document, this is `true`; otherwise, it is `false`. Note that the implementation is in charge of this attribute, not the user. If the user changes the value of the attribute (even if it ends up having the same value as the default value) then the `specified` flag is automatically flipped to `true`. To re-specify the attribute as the default value from the DTD, the user must delete the attribute. The implementation will then make a new attribute available with `specified` set to `false` and the default value (if one exists).

      In summary:

      - If the attribute has an assigned value in the document then `specified` is `true`, and the value is the assigned value.
      - If the attribute has no assigned value in the document and has a default value in the DTD, then `specified` is `false`, and the value is the default value in the DTD.
      - If the attribute has no assigned value in the document and has a value of #IMPLIED in the DTD, then the attribute does not appear in the structure model of the document.
    `value`
      On retrieval, the value of the attribute is returned as a string. Character and general entity references are replaced with their values.

      On setting, this creates a `Text` node with the unparsed contents of the string.

Interface Element

  By far the vast majority of objects (apart from text) that authors encounter when traversing a document are `Element` nodes. Assume the following XML document:

      <elementExample id="demo">
        <subelement1/>
        <subelement2><subsubelement/></subelement2>
      </elementExample>

  When represented using DOM, the top node is an `Element` node for "elementExample", which contains two child `Element` nodes, one for "subelement1" and one for "subelement2". "subelement1" contains no child nodes.

  Elements may have attributes associated with them; since the `Element` interface inherits from `Node`, the generic `Node` interface method `getAttributes` may be used to retrieve the set of all attributes for an element. There are methods on the `Element` interface to retrieve either an `Attr` object by name or an attribute value by name. In XML, where an attribute value may contain entity references, an `Attr` object should be retrieved to examine the possibly fairly complex sub-tree representing the attribute value. On the other hand, in HTML, where all attributes have simple string values, methods to directly access an attribute value can safely be used as a convenience.

  IDL Definition

        interface Element : Node {
          readonly attribute  DOMString            tagName;
          DOMString                 getAttribute(in DOMString name);
          void                      setAttribute(in DOMString name,
                                                 in DOMString value)
                                                 raises(DOMException);
          void                      removeAttribute(in DOMString name)
                                                    raises(DOMException);
          Attr                      getAttributeNode(in DOMString name);
          Attr                      setAttributeNode(in Attr newAttr)
                                                     raises(DOMException);
          Attr                      removeAttributeNode(in Attr oldAttr)
                                                        raises(DOMException);
          NodeList                  getElementsByTagName(in DOMString name);
          void                      normalize();
        };

  Attributes
    `tagName`
      The name of the element. For example, in:

          <elementExample id="demo">
                  ...
          </elementExample> ,

      `tagName` has the value `"elementExample"`. Note that this is case-preserving in XML, as are all of the operations of the DOM. The HTML DOM returns the `tagName` of an HTML element in the canonical uppercase form, regardless of the case in the source HTML document.
  Methods
    `getAttribute`
      Retrieves an attribute value by name.
      Parameters

        `name` |  | The name of the attribute to retrieve.

      Return Value
        The `Attr` value as a string, or the empty string if that attribute does not have a specified or default value.
      This method raises no exceptions.
    `setAttribute`
      Adds a new attribute. If an attribute with that name is already present in the element, its value is changed to be that of the value parameter. This value is a simple string, it is not parsed as it is being set. So any markup (such as syntax to be recognized as an entity reference) is treated as literal text, and needs to be appropriately escaped by the implementation when it is written out. In order to assign an attribute value that contains entity references, the user must create an `Attr` node plus any `Text` and `EntityReference` nodes, build the appropriate subtree, and use `setAttributeNode` to assign it as the value of an attribute.
      Parameters

        `name` |  | The name of the attribute to create or alter.
        `value` |  | Value to set in string form.

      Exceptions
        `DOMException`

          INVALID_CHARACTER_ERR: Raised if the specified name contains an invalid character.

          NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.

      This method returns nothing.
    `removeAttribute`
      Removes an attribute by name. If the removed attribute has a default value it is immediately replaced.
      Parameters

        `name` |  | The name of the attribute to remove.

      Exceptions
        `DOMException`

          NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.

      This method returns nothing.
    `getAttributeNode`
      Retrieves an `Attr` node by name.
      Parameters

        `name` |  | The name of the attribute to retrieve.

      Return Value
        The `Attr` node with the specified attribute name or `null` if there is no such attribute.
      This method raises no exceptions.
    `setAttributeNode`
      Adds a new attribute. If an attribute with that name is already present in the element, it is replaced by the new one.
      Parameters

        `newAttr` |  | The `Attr` node to add to the attribute list.

      Return Value
        If the `newAttr` attribute replaces an existing attribute with the same name, the previously existing `Attr` node is returned, otherwise `null` is returned.
      Exceptions
        `DOMException`

          WRONG_DOCUMENT_ERR: Raised if `newAttr` was created from a different document than the one that created the element.

          NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.

          INUSE_ATTRIBUTE_ERR: Raised if `newAttr` is already an attribute of another `Element` object. The DOM user must explicitly clone `Attr` nodes to re-use them in other elements.

    `removeAttributeNode`
      Removes the specified attribute.
      Parameters

        `oldAttr` |  | The `Attr` node to remove from the attribute list. If the removed `Attr` has a default value it is immediately replaced.

      Return Value
        The `Attr` node that was removed.
      Exceptions
        `DOMException`

          NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.

          NOT_FOUND_ERR: Raised if `oldAttr` is not an attribute of the element.

    `getElementsByTagName`
      Returns a `NodeList` of all descendant elements with a given tag name, in the order in which they would be encountered in a preorder traversal of the `Element` tree.
      Parameters

        `name` |  | The name of the tag to match on. The special value "*" matches all tags.

      Return Value
        A list of matching `Element` nodes.
      This method raises no exceptions.
    `normalize`
      Puts all `Text` nodes in the full depth of the sub-tree underneath this `Element` into a "normal" form where only markup (e.g., tags, comments, processing instructions, CDATA sections, and entity references) separates `Text` nodes, i.e., there are no adjacent `Text` nodes. This can be used to ensure that the DOM view of a document is the same as if it were saved and re-loaded, and is useful when operations (such as XPointer lookups) that depend on a particular document tree structure are to be used.
      This method has no parameters.
      This method returns nothing.
      This method raises no exceptions.

Interface Text

  The `Text` interface represents the textual content (termed character data in XML) of an `Element` or `Attr`. If there is no markup inside an element's content, the text is contained in a single object implementing the `Text` interface that is the only child of the element. If there is markup, it is parsed into a list of elements and `Text` nodes that form the list of children of the element.

  When a document is first made available via the DOM, there is only one `Text` node for each block of text. Users may create adjacent `Text` nodes that represent the contents of a given element without any intervening markup, but should be aware that there is no way to represent the separations between these nodes in XML or HTML, so they will not (in general) persist between DOM editing sessions. The `normalize()` method on `Element` merges any such adjacent `Text` objects into a single node for each block of text; this is recommended before employing operations that depend on a particular document structure, such as navigation with `XPointers.`

  IDL Definition

        interface Text : CharacterData {
          Text                      splitText(in unsigned long offset)
                                              raises(DOMException);
        };

  Methods
    `splitText`
      Breaks this `Text` node into two Text nodes at the specified offset, keeping both in the tree as siblings. This node then only contains all the content up to the `offset` point. And a new `Text` node, which is inserted as the next sibling of this node, contains all the content at and after the `offset` point.
      Parameters

        `offset` |  | The offset at which to split, starting from 0.

      Return Value
        The new `Text` node.
      Exceptions
        `DOMException`

          INDEX_SIZE_ERR: Raised if the specified offset is negative or greater than the number of characters in `data`.

          NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.

Interface Comment

  This represents the content of a comment, i.e., all the characters between the starting '`<!--`' and ending '`-->`'. Note that this is the definition of a comment in XML, and, in practice, HTML, although some HTML tools may implement the full SGML comment structure.

  IDL Definition

        interface Comment : CharacterData {
        };

## 1.3. Extended Interfaces

The interfaces defined here form part of the DOM Level 1 Core specification, but objects that expose these interfaces will never be encountered in a DOM implementation that deals only with HTML. As such, HTML-only DOM implementations do not need to have objects that implement these interfaces.

Interface CDATASection

  CDATA sections are used to escape blocks of text containing characters that would otherwise be regarded as markup. The only delimiter that is recognized in a CDATA section is the "]]>" string that ends the CDATA section. CDATA sections can not be nested. The primary purpose is for including material such as XML fragments, without needing to escape all the delimiters.

  The `DOMString` attribute of the `Text` node holds the text that is contained by the CDATA section. Note that this may contain characters that need to be escaped outside of CDATA sections and that, depending on the character encoding ("charset") chosen for serialization, it may be impossible to write out some characters as part of a CDATA section.

  The `CDATASection` interface inherits the `CharacterData` interface through the `Text` interface. Adjacent `CDATASections` nodes are not merged by use of the Element.normalize() method.

  IDL Definition

        interface CDATASection : Text {
        };

Interface DocumentType

  Each `Document` has a `doctype` attribute whose value is either `null` or a `DocumentType` object. The `DocumentType` interface in the DOM Level 1 Core provides an interface to the list of entities that are defined for the document, and little else because the effect of namespaces and the various XML scheme efforts on DTD representation are not clearly understood as of this writing.

  The DOM Level 1 doesn't support editing `DocumentType` nodes.

  IDL Definition

        interface DocumentType : Node {
          readonly attribute  DOMString            name;
          readonly attribute  NamedNodeMap         entities;
          readonly attribute  NamedNodeMap         notations;
        };

  Attributes
    `name`
      The name of DTD; i.e., the name immediately following the `DOCTYPE` keyword.
    `entities`
      A `NamedNodeMap` containing the general entities, both external and internal, declared in the DTD. Duplicates are discarded. For example in:

          <!DOCTYPE ex SYSTEM "ex.dtd" [
            <!ENTITY foo "foo">
            <!ENTITY bar "bar">
            <!ENTITY % baz "baz">
          ]>
          <ex/>

      the interface provides access to `foo` and `bar` but not `baz`. Every node in this map also implements the `Entity` interface.

      The DOM Level 1 does not support editing entities, therefore `entities` cannot be altered in any way.

    `notations`
      A `NamedNodeMap` containing the notations declared in the DTD. Duplicates are discarded. Every node in this map also implements the `Notation` interface.

      The DOM Level 1 does not support editing notations, therefore `notations` cannot be altered in any way.

Interface Notation

  This interface represents a notation declared in the DTD. A notation either declares, by name, the format of an unparsed entity (see section 4.7 of the XML 1.0 specification), or is used for formal declaration of Processing Instruction targets (see section 2.6 of the XML 1.0 specification). The `nodeName` attribute inherited from `Node` is set to the declared name of the notation.

  The DOM Level 1 does not support editing `Notation` nodes; they are therefore readonly.

  A `Notation` node does not have any parent.

  IDL Definition

        interface Notation : Node {
          readonly attribute  DOMString            publicId;
          readonly attribute  DOMString            systemId;
        };

  Attributes
    `publicId`
      The public identifier of this notation. If the public identifier was not specified, this is `null`.
    `systemId`
      The system identifier of this notation. If the system identifier was not specified, this is `null`.

Interface Entity

  This interface represents an entity, either parsed or unparsed, in an XML document. Note that this models the entity itself not the entity declaration. `Entity` declaration modeling has been left for a later Level of the DOM specification.

  The `nodeName` attribute that is inherited from `Node` contains the name of the entity.

  An XML processor may choose to completely expand entities before the structure model is passed to the DOM; in this case there will be no `EntityReference` nodes in the document tree.

  XML does not mandate that a non-validating XML processor read and process entity declarations made in the external subset or declared in external parameter entities. This means that parsed entities declared in the external subset need not be expanded by some classes of applications, and that the replacement value of the entity may not be available. When the replacement value is available, the corresponding `Entity` node's child list represents the structure of that replacement text. Otherwise, the child list is empty.

  The resolution of the children of the `Entity` (the replacement value) may be lazily evaluated; actions by the user (such as calling the `childNodes` method on the `Entity` Node) are assumed to trigger the evaluation.

  The DOM Level 1 does not support editing `Entity` nodes; if a user wants to make changes to the contents of an `Entity`, every related `EntityReference` node has to be replaced in the structure model by a clone of the `Entity`'s contents, and then the desired changes must be made to each of those clones instead. All the descendants of an `Entity` node are readonly.

  An `Entity` node does not have any parent.

  IDL Definition

        interface Entity : Node {
          readonly attribute  DOMString            publicId;
          readonly attribute  DOMString            systemId;
          readonly attribute  DOMString            notationName;
        };

  Attributes
    `publicId`
      The public identifier associated with the entity, if specified. If the public identifier was not specified, this is `null`.
    `systemId`
      The system identifier associated with the entity, if specified. If the system identifier was not specified, this is `null`.
    `notationName`
      For unparsed entities, the name of the notation for the entity. For parsed entities, this is `null`.

Interface EntityReference

  `EntityReference` objects may be inserted into the structure model when an entity reference is in the source document, or when the user wishes to insert an entity reference. Note that character references and references to predefined entities are considered to be expanded by the HTML or XML processor so that characters are represented by their Unicode equivalent rather than by an entity reference. Moreover, the XML processor may completely expand references to entities while building the structure model, instead of providing `EntityReference` objects. If it does provide such objects, then for a given `EntityReference` node, it may be that there is no `Entity` node representing the referenced entity; but if such an `Entity` exists, then the child list of the `EntityReference` node is the same as that of the `Entity` node. As with the `Entity` node, all descendants of the `EntityReference` are readonly.

  The resolution of the children of the `EntityReference` (the replacement value of the referenced `Entity`) may be lazily evaluated; actions by the user (such as calling the `childNodes` method on the `EntityReference` node) are assumed to trigger the evaluation.

  IDL Definition

        interface EntityReference : Node {
        };

Interface ProcessingInstruction

  The `ProcessingInstruction` interface represents a "processing instruction", used in XML as a way to keep processor-specific information in the text of the document.

  IDL Definition

        interface ProcessingInstruction : Node {
          readonly attribute  DOMString            target;
                   attribute  DOMString            data;
                                              // raises(DOMException) on setting
        };

  Attributes
    `target`
      The target of this processing instruction. XML defines this as being the first token following the markup that begins the processing instruction.
    `data`
      The content of this processing instruction. This is from the first non white space character after the target to the character immediately preceding the `?>`.
      Exceptions on setting
        `DOMException`

          NO_MODIFICATION_ALLOWED_ERR: Raised when the node is readonly.