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1. Document Object Model XPath

Editor:: Ray Whitmer, Netscape/AOL

1.1. Introduction
1.2. Mapping DOM to XPath
1.3. Interfaces
- XPathException, XPathExceptionCode, XPathEvaluator, XPathExpression, XPathNSResolver, XPathResult, XPathNamespace

1.1. Introduction

XPath 1.0 [XPath 1.0] is becoming an important part of a variety of many specifications including XForms, XPointer, XSL, XML Query, and so on. It is also a clear advantage for user applications which use DOM to be able to use XPath expressions to locate nodes automatically and declaratively. But liveness issues have plagued each attempt to get a list of DOM nodes matching specific criteria, as would be expected for an XPath API. There have also traditionally been model mismatches between DOM and XPath. This proposal specifies new interfaces and approaches to resolving these issues.

Issue XPath-2:: There should be a function to generate an XPath expression which addresses any arbitrary node within the DOM.
Resolution: Out of scope.
That is out of scope for the current requirements of this module. It could be a quite useful feature but probably not as a part of this module.

1.2. Mapping DOM to XPath

This section considers the differences between the Document Object Model [DOM Level 3 Core] and the XPath 1.0 model [XPath 1.0].

1.2.1. Text Nodes

The XPath model relies on the XML Information Set [XML Information set] ands represents Character Information Items in a single logical text node where DOM may have multiple fragmented Text nodes due to cdata sections, entity references, etc. Instead of returning multiple nodes where XPath sees a single logical text node, only the first non-empty DOM Text or CDATASection node of any logical XPath text will be returned in the node set. Applications using XPath in an environment with fragmented text nodes must manually gather the text of a single logical text node possibly from multiple nodes beginning with the first Text node or CDATASection node returned by the implementation.

Note: In an attempt to better implement the XML Information Set, DOM Level 3 Core [DOM Level 3 Core] adds the attribute wholeText on the Text interface for retrieving the whole text for logically-adjacent Text nodes and the method replaceWholeText for replacing those nodes.

1.2.2. Namespace Nodes

The XPath model expects namespace nodes for each in-scope namespace to be attached to each element. DOM and certain other W3C Information Set conformant implementations only maintain the declaration of namespaces instead of replicating them on each Element where they are in-scope. The DOM implementation of XPath returns a new node of type XPATH_NAMESPACE_NODE, defined in the XPathNamespace interface, to properly preserve identity and ordering. This node type is only visible using the XPath evaluation methods.

1.2.3. Document order

The document order of nodes in the DOM Core has been defined to be compatible with the XPath document order. The XPath DOM is extending the document order of the DOM Core to include the XPathNamespace nodes. Element nodes occur before their children. The attribute nodes and namespace nodes of an element occur before the children of the element. The namespace nodes are defined to occur before the attribute nodes. The relative order of namespace nodes is implementation-dependent. The relative order of attribute nodes is implementation-dependent. The compareTreePosition method on the Node interface defined in the DOM Core must compare the XPathNamespace nodes using this extending document order if the XPath DOM module is supported.

1.3. Interfaces

A DOM application may use the hasFeature(feature, version) method of the DOMImplementation interface with parameter values "XPath" and "3.0" (respectively) to determine whether or not the event module is supported by the implementation. In order to fully support this module, an implementation must also support the "Core" feature defined in the DOM Level 3 Core specification [DOM Level 3 Core]. Please, refer to additional information about conformance in the DOM Level 3 Core specification [DOM Level 3 Core].

Exception XPathException

A new exception has been created for exceptions specific to these XPath interfaces.

IDL Definition

exception XPathException {
  unsigned short   code;
};
// XPathExceptionCode
const unsigned short      INVALID_EXPRESSION_ERR         = 1;
const unsigned short      TYPE_ERR                       = 2;

Definition group XPathExceptionCode

Defined Constants

INVALID_EXPRESSION_ERR

If the expression is not a legal expression according to the rules of the specific XPathEvaluator. If the XPathEvaluator was obtained by casting the document, the expression must be XPath 1.0 with no special extension functions.

Issue XPath-4:: A separate exception should be raised if there are problems resolving namespaces.
Resolution: Yes. These now raise DOMException with the code NAMESPACE_ERR.

TYPE_ERR

If the expression cannot be converted to return the specified type.

Interface XPathEvaluator

The evaluation of XPath expressions is provided by XPathEvaluator, which will provide evaluation of XPath 1.0 expressions with no specialized extension functions or variables. It is expected that the XPathEvaluator interface will be implemented on the same object which implements the Document interface in an implementation which supports the XPath DOM module. XPathEvaluator implementations may be available from other sources that may provide support for new versions of XPath or special extension functions or variables which are not defined in this specification.

Issue XPath-16:: The methods of XPathExpression should be named with more-XPath- specific names because the interface will often be implemented by the same object which implements document.
Resolution: No change.
The point of interfaces is to localize the implementing namespace. This would make the method names unnecessarily long and complex even though there are no conflicts in the interface itself. The new core method getInterface is designed for discovering interfaces of additional modules that may not be directly implemented on the objects to which they are attached. This could be used to implement XPath on a separate object. The user only refers to the separate interfaces and not the proprietary aggregate implementation.
Issue XPath-22:: Should entity refs be supported so that queries can be made on them?
Resolution: No change.
We will not do this now. They are not part of the XPath data model. Note that they may be present in the hierarchy of returned nodes, but may not directly be requested or returned in the node set.
Issue XPath-24:: What does createResult create when one wants to resuse the XPath?
Resolution: It is not useful.
Removed method.
Issue XPath-27:: Should ordering be a separate flag, or a type of result that can be requested. As a type of result, it can be better optimized in implementations.
Resolution: It makes sense as a type of result. Changed.
Removed method.

IDL Definition

interface XPathEvaluator {
  XPathExpression    createExpression(in DOMString expression, 
                                      in XPathNSResolver resolver)
                                        raises(XPathException, 
                                               DOMException);
  XPathNSResolver    createNSResolver(in Node nodeResolver);
  XPathResult        evaluate(in DOMString expression, 
                              in Node contextNode, 
                              in XPathNSResolver resolver, 
                              in unsigned short type, 
                              in XPathResult result)
                                        raises(XPathException, 
                                               DOMException);
};

Methods

createExpression

Creates a parsed XPath expression with resolved namespaces. This is useful when an expression will be reused in an application since it makes it possible to compile the expression string into a more efficient internal form and preresolve all namespace prefixes which occur within the expression.

Issue XPath-5:: createExpression should not raise exceptions about type coercion.
Resolution: This was already fixed in the public draft.

Parameters

expression of type DOMString: The XPath expression string to be parsed.
resolver of type XPathNSResolver: The resolver permits translation of prefixes within the XPath expression into appropriate namespace URIs. If this is specified as null, any namespace prefix within the expression will result in DOMException being thrown with the code NAMESPACE_ERR.

Return Value

XPathExpression

The compiled form of the XPath expression.

Exceptions

`XPathException`	INVALID_EXPRESSION_ERR: Raised if the expression is not legal according to the rules of the `XPathEvaluator`i
`DOMException`	NAMESPACE_ERR: Raised if the expression contains namespace prefixes which cannot be resolved by the specified `XPathNSResolver`.

createNSResolver

Adapts any DOM node to resolve namespaces so that an XPath expression can be easily evaluated relative to the context of the node where it appeared within the document. This adapter works by calling the method lookupNamespacePrefix on Node.

Issue XPath-6:: It should be possible to create an XPathNSResolver that does not rely on a node, but which implements a map of resolutions that can be added to by the application.
Resolution: No change.
The application can easily create this, which was why the interface was designed as it is. The specification will not require a specific factory at this time for application populated maps.
Issue XPath-14:: There should be type restrictions on which types of nodes may be adapted by createNSResolver.
Resolution: No change.
The namespace methods on the Node interface of the Level 3 core may be called without exception on all node types. In some cases no non-null namespace resolution will ever be returned. That is what may also be expected of this adapter.

Parameters

nodeResolver of type Node: The node to be used as a context for namespace resolution.

Return Value

XPathNSResolver

XPathNSResolver which resolves namespaces with respect to the definitions in scope for a specified node.

No Exceptions

evaluate

Evaluates an XPath expression string and returns a result of the specified type if possible.

Issue XPath-17-18:: An exception needs to be raised when an XPath expression is evaluated on a node such as an EntityReference which cannot serve as an XPath context node.
Resolution: Done: NOT_SUPPORTED_ERR.
Issue XPath-19:: A description is needed of what happens when the node passed to the evaluation function is a Text or CDATASection in the DOM case where the text may be fragmented between text nodes.
Resolution: Done.
Issue XPath-20:: Eliminate the evaluate method from XPathEvaluator, forcing everyone to create expressions.
Resolution: No change.
Any implementor can easily implement it by creating an expression. Having it available as a separate routine is a convenience and may be an optimization as well in some cases.
Issue XPath-21:: Revert to multiple evaluateAs methods instead of passing a type code.
Resolution: No change.
This is an alternative which eliminates a method argument while adding methods, but the type code is used to designate the type on returns anyway and using it as an argument to specify any coercion seems natural to many.
Issue XPath-13:: Error exceptions are needed when there is a mismatch between the implementation of XPathEvaluator and the context node being evaluated.
Resolution: Done: WRONG_DOCUMENT_ERR

Parameters

expression of type DOMString: The XPath expression string to be parsed and evaluated.
contextNode of type Node: The context is context node for the evaluation of this XPath expression. If the XPathEvaluator was obtained by casting the Document then this must be owned by the same document and must be a Document, Element, Attribute, Text, CDATASection, Comment, ProcessingInstruction, or XPathNamespace node. If the context node is a Text or a CDATASection, then the context is interpreted as the whole logical text node as seen by XPath, unless the node is empty in which case it may not serve as the XPath context.
resolver of type XPathNSResolver: The resolver permits translation of prefixes within the XPath expression into appropriate namespace URIs. If this is specified as null, any namespace prefix within the expression will result in DOMException being thrown with the code NAMESPACE_ERR.
type of type unsigned short: If a specific type is specified, then the result will be coerced to return the specified type relying on XPath conversions and fail if the desired coercion is not possible. This must be one of the type codes of XPathResult.
result of type XPathResult: The result specifies a specific XPathResult which may be reused and returned by this method. If this is specified as null or the implementation cannot reuse the specified result, a new XPathResult will be constructed and returned.

Return Value

XPathResult

The result of the evaluation of the XPath expression.

Exceptions

XPathException

INVALID_EXPRESSION_ERR: Raised if the expression is not legal according to the rules of the XPathEvaluatori

TYPE_ERR: Raised if the result cannot be converted to return the specified type.

DOMException

NAMESPACE_ERR: Raised if the expression contains namespace prefixes which cannot be resolved by the specified XPathNSResolver.

WRONG_DOCUMENT_ERR: The Node is from a document that is not supported by this XPathEvaluator.

NOT_SUPPORTED_ERR: The Node is not a type permitted as an XPath context node.

Interface XPathExpression

The XPathExpression interface represents a parsed and resolved XPath expression.

Issue XPath-8:: The evaluateExpression method should be moved to the XPathExpression interface so you do not have to use / pass two interfaces just to use it.
Resolution: Done.
Issue XPath-15:: XPathExpression should have a public reference to the XPathEvaluator that created it.
Resolution: No change.
Lacks justification.

IDL Definition

interface XPathExpression {
  XPathResult        evaluate(in Node contextNode, 
                              in unsigned short type, 
                              in XPathResult result)
                                        raises(XPathException, 
                                               DOMException);
};

Methods

evaluate

Evaluates this XPath expression and returns a result.

Parameters

contextNode of type Node: The context is context node for the evaluation of this XPath expression.
If the XPathEvaluator was obtained by casting the Document then this must be owned by the same document and must be a Document, Element, Attribute, Text, CDATASection, Comment, ProcessingInstruction, or XPathNamespace node.
If the context node is a Text or a CDATASection, then the context is interpreted as the whole logical text node as seen by XPath, unless the node is empty in which case it may not serve as the XPath context.
type of type unsigned short: If a specific type is specified, then the result will be coerced to return the specified type relying on XPath conversions and fail if the desired coercion is not possible. This must be one of the type codes of XPathResult.
result of type XPathResult: The result specifies a specific XPathResult to be reused and returned by this method. If this is specified as null, a new XPathResult will be constructed and returned. Any XPathResult which was not created by this XPathEvaluator may be ignored as though a null were passed as the parameter.

Return Value

XPathResult

The result of the evaluation of the XPath expression.

Exceptions

XPathException

TYPE_ERR: Raised if the result cannot be converted to return the specified type.

DOMException

WRONG_DOCUMENT_ERR: The Node is from a document that is not supported by the XPathExpression that created this XPathExpression.

NOT_SUPPORTED_ERR: The Node is not a type permitted as an XPath context node.

Interface XPathNSResolver

The XPathNSResolver interface permit prefix strings in the expression to be properly bound to namespaceURI strings. XPathEvaluator can construct an implementation of XPathNSResolver from a node, or the interface may be implemented by any application.

IDL Definition

interface XPathNSResolver {
  DOMString          lookupNamespaceURI(in DOMString prefix);
};

Methods

lookupNamespaceURI

Look up the namespace URI associated to the given namespace prefix. The XPath evaluator must never call this with a null or empty argument, because the result of doing this is undefined.

Issue XPath-9:: Null / empty prefix passed to XPathNSResolver should return default namespace.
Resolution: Do not permit null to be passed in invocation, allowing the implementation, if shared, to do anything it wants with a passed null.
It would be confusing to specify more than this since the resolution of namespaces for XPath expressions never requires the default namespace.
Issue XPath-10:: Null returns are problematic.
Resolution: No change.
They should be adequately addressed in core. Some implementations have not properly supported them, but they will be fixed to be compliant. Bindings are still free to choose alternative representations of null where required.

Parameters

prefix of type DOMString: The prefix to look for.

Return Value

DOMString

Returns the associated namespace URI or null if none is found.

No Exceptions

Interface XPathResult

The XPathResult interface represents the result of the evaluation of an XPath expression within the context of a particular node. Since evaluation of an XPath expression can result in various result types, this object makes it possible to discover and manipulate the type and value of the result.

Issue XPath-23:: Should there be a flag on the result to say whether an iteration has become invalid?
Resolution: Yes.
Added the boolean attribute invalidIteratorState
Issue XPath-25:: Should there be a reset method on the result in case someone wants to iterate the result multiple times?
It may be more trouble than it is worth, because the user can request a new query. See if there are use cases.
Issue XPath-26:: It might be better to consolidate the interfaces and just move the snapshot and iterator functions to the result object.
Resolution: Yes.
The result of the consolidation looks good and unless there are great objections, this is how it will be.

IDL Definition

interface XPathResult {

  // XPathResultType
  const unsigned short      ANY_TYPE                       = 0;
  const unsigned short      NUMBER_TYPE                    = 1;
  const unsigned short      STRING_TYPE                    = 2;
  const unsigned short      BOOLEAN_TYPE                   = 3;
  const unsigned short      UNORDERED_NODE_ITERATOR_TYPE   = 4;
  const unsigned short      ORDERED_NODE_ITERATOR_TYPE     = 5;
  const unsigned short      UNORDERED_NODE_SNAPSHOT_TYPE   = 6;
  const unsigned short      ORDERED_NODE_SNAPSHOT_TYPE     = 7;
  const unsigned short      ANY_UNORDERED_NODE_TYPE        = 8;
  const unsigned short      FIRST_ORDERED_NODE_TYPE        = 9;

  readonly attribute unsigned short  resultType;
  readonly attribute double          numberValue;
                                        // raises(XPathException) on retrieval

  readonly attribute DOMString       stringValue;
                                        // raises(XPathException) on retrieval

  readonly attribute boolean         booleanValue;
                                        // raises(XPathException) on retrieval

  readonly attribute Node            singleNodeValue;
                                        // raises(XPathException) on retrieval

  readonly attribute boolean         invalidIteratorState;
  readonly attribute unsigned long   snapshotLength;
                                        // raises(XPathException) on retrieval

  Node               iterateNext()
                                        raises(XPathException, 
                                               DOMException);
  Node               snapshotItem(in unsigned long index)
                                        raises(XPathException);
};

Definition group XPathResultType

An integer indicating what type of result this is.

Defined Constants

ANY_TYPE: This code does not represent a specific type. An evaluation of an XPath expression will never produce this type. If this type is requested, then the evaluation must return whatever type naturally results from evaluation of the expression.
ANY_UNORDERED_NODE_TYPE: The result is a node set as defined by XPath 1.0 and will be accessed as a single node, which may be null if the node set is empty. Document modification does not invalidate the node, but may mean that the result node no longer corresponds to the current document. This is a convenience that permits optimization where the caller knows that no more than one such node exists because evaluation can stop after finding the one node of an expression that would otherwise return a node set.
If there are more than one node in the actual result, the single node returned may not be the first.
BOOLEAN_TYPE: The result is a boolean as defined by XPath 1.0. Document modification does not invalidate the boolean, but may mean that the boolean no longer corresponds to the current document.
FIRST_ORDERED_NODE_TYPE: The result is a node set as defined by XPath 1.0 and will be accessed as a single node, which may be null if the node set is empty. Document modification does not invalidate the node, but may mean that the result node no longer corresponds to the current document. This is a convenience that permits optimization where the implementation is naturally producing document order and the caller knows that no more than one such node exists because evaluation can stop after finding the one node of an expression that would otherwise return a node set.
If there are more than one node in the actual result, the single node returned will be the first.
NUMBER_TYPE: The result is a number as defined by XPath 1.0. Document modification does not invalidate the number, but may mean that the number no longer corresponds to the current document.
ORDERED_NODE_ITERATOR_TYPE: The result is a node set as defined by XPath 1.0 that will be accessed iteratively, which will produce document-ordered nodes. Document modification invalidates the iteration.
ORDERED_NODE_SNAPSHOT_TYPE: The result is a node set as defined by XPath 1.0 that will be accessed as a snapshot list of nodes that will be in original document order. Document modification does not invalidate the snapshot, but may mean that the snapshot no longer corresponds to the current document.
STRING_TYPE: The result is a string as defined by XPath 1.0. Document modification does not invalidate the string, but may mean that the string no longer corresponds to the current document.
UNORDERED_NODE_ITERATOR_TYPE: The result is a node set as defined by XPath 1.0 that will be accessed iteratively, which may not produce nodes in a particular order. Document modification invalidates the iteration.
This is the default type returned if the result is a node set and ANY_TYPE is requested.
UNORDERED_NODE_SNAPSHOT_TYPE: The result is a node set as defined by XPath 1.0 that will be accessed as a snapshot list of nodes that may not be in a particular order. Document modification does not invalidate the snapshot but may mean that the snapshot no longer corresponds to the current document.

Attributes

booleanValue of type boolean, readonly

The value of this boolean result.

Exceptions on retrieval

XPathException

TYPE_ERR: raised if resultType is not BOOLEAN_TYPE.

invalidIteratorState of type boolean, readonly

Signifies that the iterator has become invalid. True ifresultType is UNORDERED_NODE_ITERATOR_TYPE or ORDERED_NODE_ITERATOR_TYPE and the document has beem modified since this result was returned.

numberValue of type double, readonly

The value of this number result.

Exceptions on retrieval

XPathException

TYPE_ERR: raised if resultType is not NUMBER_TYPE.

resultType of type unsigned short, readonly

A code representing the type of this result, as defined by the type constants.

singleNodeValue of type Node, readonly

The value of this single node result, which may be null.

Exceptions on retrieval

XPathException

TYPE_ERR: raised if resultType is not ANY_UNORDERED_NODE_TYPE or FIRST_ORDERED_NODE_TYPE.

snapshotLength of type unsigned long, readonly

The number of nodes in the result snapshot. Valid values for snapshotItem indices are 0 to snapshotLength-1 inclusive.

Exceptions on retrieval

XPathException

TYPE_ERR: raised if resultType is not UNORDERED_NODE_SNAPSHOT_TYPE or ORDERED_NODE_SNAPSHOT_TYPE.

stringValue of type DOMString, readonly

The value of this string result.

Exceptions on retrieval

XPathException

TYPE_ERR: raised if resultType is not STRING_TYPE.

Methods

iterateNext

Iterates and returns the next node from the node set or null if there are no more nodes.

Return Value

Node

Returns the next node.

Exceptions

`XPathException`	TYPE_ERR: raised if `resultType` is not `UNORDERED_NODE_ITERATOR_TYPE` or `ORDERED_NODE_ITERATOR_TYPE`.
`DOMException`	INVALID_STATE_ERR: The document has been mutated since the result was returned.

No Parameters

snapshotItem

Returns the indexth item in the snapshot collection. If index is greater than or equal to the number of nodes in the list, this method returns null. Unlike the iterator result, the snapshot does not become invalid, but may not correspond to the current document if it is mutated.

Parameters

index of type unsigned long: Index into the snapshot collection.

Return Value

Node

The node at the indexth position in the NodeList, or null if that is not a valid index.

Exceptions

XPathException

TYPE_ERR: raised if resultType is not UNORDERED_NODE_SNAPSHOT_TYPE or ORDERED_NODE_SNAPSHOT_TYPE.

Interface XPathNamespace

The XPathNamespace interface is returned by XPathResult interfaces to represent the XPath namespace node type that DOM lacks. There is no public constructor for this node type. Attempts to place it into a hierarchy or a NamedNodeMap result in a DOMException with the code HIERARCHY_REQUEST_ERR. This node is read only, so methods or setting of attributes that would mutate the node result in a DOMException with the code NO_MODIFICATION_ALLOWED_ERR.

The core specification describes attributes of the Node interface that are different for different node node types but does not describe XPATH_NAMESPACE_NODE, so here is a description of those attributes for this node type. All attributes of Node not described in this section have a null or false value.

ownerDocument matches the ownerDocument of the ownerElement even if the element is later adopted.

prefix is the prefix of the namespace represented by the node.

NodeName is the same as prefix.

NodeType is equal to XPATH_NAMESPACE_NODE.

namespaceURI is the namespace URI of the namespace represented by the node.

adoptNode, cloneNode, and importNode fail on this node type by raising a DOMException with the code NOT_SUPPORTED_ERR.

Issue XPath-12:: importNode should also fail on XPathNamespace nodes.
Resolution: This was already fixed in the public draft.
Issue XPath-3:: The Namespace node should be added to DOM Level 3 core and should be available via a read-only NamedNodeMap on element to reduce the confusion of adding a special node type for XPath.
Resolution: No change.
There are no known problems with this add-on node type and uses beyond XPath are not anticipated.
Issue XPath-11:: Node.namespaceValue should be identical to Node.namespaceURI and not null.
Resolution: No change.
It is not clear why it should be this way since the infoset does not dictate it.

IDL Definition

interface XPathNamespace : Node {

  // XPathNodeType
  const unsigned short      XPATH_NAMESPACE_NODE           = 13;

  readonly attribute Element         ownerElement;
};

Definition group XPathNodeType

An integer indicating which type of node this is.

Note: There is currently only one type of node which is specific to XPath. The numbers in this list must not collide with the values assigned to core node types.

Defined Constants

XPATH_NAMESPACE_NODE: The node is a Namespace.

Attributes

ownerElement of type Element, readonly: The Element on which the namespace was in scope when it was requested. This does not change on a returned namespace node even if the document changes such that the namespace goes out of scope on that element and this node is no longer found there by XPath.

Appendix A: IDL Definitions

This appendix contains the complete OMG IDL [OMGIDL] for the Level 3 Document Object Model XPath definitions.

The IDL files are also available as: http://www.w3.org/TR/2002/WD-DOM-Level-3-XPath-20020208/idl.zip

xpath.idl:

// File: xpath.idl

#ifndef _XPATH_IDL_
#define _XPATH_IDL_

#include "dom.idl"

#pragma prefix "dom.w3c.org"
module xpath
{

  typedef dom::DOMString DOMString;
  typedef dom::Node Node;
  typedef dom::Element Element;

  interface XPathNSResolver;
  interface XPathResult;
  interface XPathExpression;

  exception XPathException {
    unsigned short   code;
  };
  // XPathExceptionCode
  const unsigned short      INVALID_EXPRESSION_ERR         = 1;
  const unsigned short      TYPE_ERR                       = 2;


  interface XPathEvaluator {
    XPathExpression    createExpression(in DOMString expression, 
                                        in XPathNSResolver resolver)
                                        raises(XPathException, 
                                               dom::DOMException);
    XPathNSResolver    createNSResolver(in Node nodeResolver);
    XPathResult        evaluate(in DOMString expression, 
                                in Node contextNode, 
                                in XPathNSResolver resolver, 
                                in unsigned short type, 
                                in XPathResult result)
                                        raises(XPathException, 
                                               dom::DOMException);
  };

  interface XPathExpression {
    XPathResult        evaluate(in Node contextNode, 
                                in unsigned short type, 
                                in XPathResult result)
                                        raises(XPathException, 
                                               dom::DOMException);
  };

  interface XPathNSResolver {
    DOMString          lookupNamespaceURI(in DOMString prefix);
  };

  interface XPathResult {

    // XPathResultType
    const unsigned short      ANY_TYPE                       = 0;
    const unsigned short      NUMBER_TYPE                    = 1;
    const unsigned short      STRING_TYPE                    = 2;
    const unsigned short      BOOLEAN_TYPE                   = 3;
    const unsigned short      UNORDERED_NODE_ITERATOR_TYPE   = 4;
    const unsigned short      ORDERED_NODE_ITERATOR_TYPE     = 5;
    const unsigned short      UNORDERED_NODE_SNAPSHOT_TYPE   = 6;
    const unsigned short      ORDERED_NODE_SNAPSHOT_TYPE     = 7;
    const unsigned short      ANY_UNORDERED_NODE_TYPE        = 8;
    const unsigned short      FIRST_ORDERED_NODE_TYPE        = 9;

    readonly attribute unsigned short  resultType;
    readonly attribute double          numberValue;
                                        // raises(XPathException) on retrieval

    readonly attribute DOMString       stringValue;
                                        // raises(XPathException) on retrieval

    readonly attribute boolean         booleanValue;
                                        // raises(XPathException) on retrieval

    readonly attribute Node            singleNodeValue;
                                        // raises(XPathException) on retrieval

    readonly attribute boolean         invalidIteratorState;
    readonly attribute unsigned long   snapshotLength;
                                        // raises(XPathException) on retrieval

    Node               iterateNext()
                                        raises(XPathException, 
                                               dom::DOMException);
    Node               snapshotItem(in unsigned long index)
                                        raises(XPathException);
  };

  interface XPathNamespace : Node {

    // XPathNodeType
    const unsigned short      XPATH_NAMESPACE_NODE           = 13;

    readonly attribute Element         ownerElement;
  };
};

#endif // _XPATH_IDL_

Appendix B: Java Language Binding

This appendix contains the complete Java [Java] bindings for the Level 3 Document Object Model XPath.

The Java files are also available as http://www.w3.org/TR/2002/WD-DOM-Level-3-XPath-20020208/java-binding.zip

B.1: Other XPath interfaces

org/w3c/dom/xpath/XPathException.java:

package org.w3c.dom.xpath;

public class XPathException extends RuntimeException {
    public XPathException(short code, String message) {
       super(message);
       this.code = code;
    }
    public short   code;
    // XPathExceptionCode
    public static final short INVALID_EXPRESSION_ERR    = 1;
    public static final short TYPE_ERR                  = 2;

}

org/w3c/dom/xpath/XPathEvaluator.java:

package org.w3c.dom.xpath;

import org.w3c.dom.Node;
import org.w3c.dom.DOMException;

public interface XPathEvaluator {
    public XPathExpression createExpression(String expression, 
                                            XPathNSResolver resolver)
                                            throws XPathException, DOMException;

    public XPathNSResolver createNSResolver(Node nodeResolver);

    public XPathResult evaluate(String expression, 
                                Node contextNode, 
                                XPathNSResolver resolver, 
                                short type, 
                                XPathResult result)
                                throws XPathException, DOMException;

}

org/w3c/dom/xpath/XPathExpression.java:

package org.w3c.dom.xpath;

import org.w3c.dom.Node;
import org.w3c.dom.DOMException;

public interface XPathExpression {
    public XPathResult evaluate(Node contextNode, 
                                short type, 
                                XPathResult result)
                                throws XPathException, DOMException;

}

org/w3c/dom/xpath/XPathNSResolver.java:

package org.w3c.dom.xpath;

public interface XPathNSResolver {
    public String lookupNamespaceURI(String prefix);

}

org/w3c/dom/xpath/XPathResult.java:

package org.w3c.dom.xpath;

import org.w3c.dom.Node;
import org.w3c.dom.DOMException;

public interface XPathResult {
    // XPathResultType
    public static final short ANY_TYPE                  = 0;
    public static final short NUMBER_TYPE               = 1;
    public static final short STRING_TYPE               = 2;
    public static final short BOOLEAN_TYPE              = 3;
    public static final short UNORDERED_NODE_ITERATOR_TYPE = 4;
    public static final short ORDERED_NODE_ITERATOR_TYPE = 5;
    public static final short UNORDERED_NODE_SNAPSHOT_TYPE = 6;
    public static final short ORDERED_NODE_SNAPSHOT_TYPE = 7;
    public static final short ANY_UNORDERED_NODE_TYPE   = 8;
    public static final short FIRST_ORDERED_NODE_TYPE   = 9;

    public short getResultType();

    public double getNumberValue()
                                     throws XPathException;

    public String getStringValue()
                                     throws XPathException;

    public boolean getBooleanValue()
                                     throws XPathException;

    public Node getSingleNodeValue()
                                     throws XPathException;

    public boolean getInvalidIteratorState();

    public int getSnapshotLength()
                                     throws XPathException;

    public Node iterateNext()
                            throws XPathException, DOMException;

    public Node snapshotItem(int index)
                             throws XPathException;

}

org/w3c/dom/xpath/XPathNamespace.java:

package org.w3c.dom.xpath;

import org.w3c.dom.Element;
import org.w3c.dom.Node;

public interface XPathNamespace extends Node {
    // XPathNodeType
    public static final short XPATH_NAMESPACE_NODE      = 13;

    public Element getOwnerElement();

}

Appendix C: ECMAScript Language Binding

This appendix contains the complete ECMAScript [ECMAScript] binding for the Level 3 Document Object Model XPath definitions.

Properties of the XPathException Constructor function:

XPathException.INVALID_EXPRESSION_ERR: The value of the constant XPathException.INVALID_EXPRESSION_ERR is 1.
XPathException.TYPE_ERR: The value of the constant XPathException.TYPE_ERR is 2.

Objects that implement the XPathException interface:

Properties of objects that implement the XPathException interface:

code: This property is a Number.

Objects that implement the XPathEvaluator interface:

Functions of objects that implement the XPathEvaluator interface:

createExpression(expression, resolver): This function returns an object that implements the XPathExpression interface.
The expression parameter is a String.
The resolver parameter is an object that implements the XPathNSResolver interface.
This function can raise an object that implements the XPathException interface or the DOMException interface.
createNSResolver(nodeResolver): This function returns an object that implements the XPathNSResolver interface.
The nodeResolver parameter is an object that implements the Node interface.
evaluate(expression, contextNode, resolver, type, result): This function returns an object that implements the XPathResult interface.
The expression parameter is a String.
The contextNode parameter is an object that implements the Node interface.
The resolver parameter is an object that implements the XPathNSResolver interface.
The type parameter is a Number.
The result parameter is an object that implements the XPathResult interface.
This function can raise an object that implements the XPathException interface or the DOMException interface.

Objects that implement the XPathExpression interface:

Functions of objects that implement the XPathExpression interface:

evaluate(contextNode, type, result): This function returns an object that implements the XPathResult interface.
The contextNode parameter is an object that implements the Node interface.
The type parameter is a Number.
The result parameter is an object that implements the XPathResult interface.
This function can raise an object that implements the XPathException interface or the DOMException interface.

Objects that implement the XPathNSResolver interface:

Functions of objects that implement the XPathNSResolver interface:

lookupNamespaceURI(prefix): This function returns a String.
The prefix parameter is a String.

Properties of the XPathResult Constructor function:

XPathResult.ANY_TYPE: The value of the constant XPathResult.ANY_TYPE is 0.
XPathResult.NUMBER_TYPE: The value of the constant XPathResult.NUMBER_TYPE is 1.
XPathResult.STRING_TYPE: The value of the constant XPathResult.STRING_TYPE is 2.
XPathResult.BOOLEAN_TYPE: The value of the constant XPathResult.BOOLEAN_TYPE is 3.
XPathResult.UNORDERED_NODE_ITERATOR_TYPE: The value of the constant XPathResult.UNORDERED_NODE_ITERATOR_TYPE is 4.
XPathResult.ORDERED_NODE_ITERATOR_TYPE: The value of the constant XPathResult.ORDERED_NODE_ITERATOR_TYPE is 5.
XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE: The value of the constant XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE is 6.
XPathResult.ORDERED_NODE_SNAPSHOT_TYPE: The value of the constant XPathResult.ORDERED_NODE_SNAPSHOT_TYPE is 7.
XPathResult.ANY_UNORDERED_NODE_TYPE: The value of the constant XPathResult.ANY_UNORDERED_NODE_TYPE is 8.
XPathResult.FIRST_ORDERED_NODE_TYPE: The value of the constant XPathResult.FIRST_ORDERED_NODE_TYPE is 9.

Objects that implement the XPathResult interface:

Properties of objects that implement the XPathResult interface:

resultType: This read-only property is a Number.
numberValue: This read-only property is an object that implements the double interface and can raise an object that implements the XPathException interface on retrieval.
stringValue: This read-only property is a String and can raise an object that implements the XPathException interface on retrieval.
booleanValue: This read-only property is a Boolean and can raise an object that implements the XPathException interface on retrieval.
singleNodeValue: This read-only property is an object that implements the Node interface and can raise an object that implements the XPathException interface on retrieval.
invalidIteratorState: This read-only property is a Boolean.
snapshotLength: This read-only property is a Number and can raise an object that implements the XPathException interface on retrieval.

Functions of objects that implement the XPathResult interface:

iterateNext(): This function returns an object that implements the Node interface.
This function can raise an object that implements the XPathException interface or the DOMException interface.
snapshotItem(index): This function returns an object that implements the Node interface.
The index parameter is a Number.
This function can raise an object that implements the XPathException interface.

Properties of the XPathNamespace Constructor function:

XPathNamespace.XPATH_NAMESPACE_NODE: The value of the constant XPathNamespace.XPATH_NAMESPACE_NODE is 13.

Objects that implement the XPathNamespace interface:

Objects that implement the XPathNamespace interface have all properties and functions of the Node interface as well as the properties and functions defined below.

Properties of objects that implement the XPathNamespace interface:

ownerElement: This read-only property is an object that implements the Element interface.

Appendix D: Acknowledgements

Many people contributed to the DOM specifications (Level 1, 2 or 3), including members of the DOM Working Group and the DOM Interest Group. We especially thank the following:

Andrew Watson (Object Management Group), Andy Heninger (IBM), Angel Diaz (IBM), Arnaud Le Hors (W3C and IBM), Ashok Malhotra (IBM and Microsoft), Ben Chang (Oracle), Bill Smith (Sun), Bill Shea (Merrill Lynch), Bob Sutor (IBM), Chris Lovett (Microsoft), Chris Wilson (Microsoft), David Brownell (Sun), David Ezell (Hewlett Packard Company), David Singer (IBM), Dimitris Dimitriadis (Improve AB), Don Park (invited), Elena Litani (IBM), Eric Vasilik (Microsoft), Gavin Nicol (INSO), Ian Jacobs (W3C), James Clark (invited), James Davidson (Sun), Jared Sorensen (Novell), Jeroen van Rotterdam (X-Hive Corporation), Joe Kesselman (IBM), Joe Lapp (webMethods), Joe Marini (Macromedia), Johnny Stenback (Netscape/AOL), Jon Ferraiolo (Adobe), Jonathan Marsh (Microsoft), Jonathan Robie (Texcel Research and Software AG), Kim Adamson-Sharpe (SoftQuad Software Inc.), Lauren Wood (SoftQuad Software Inc., former chair), Laurence Cable (Sun), Mark Davis (IBM), Mark Scardina (Oracle), Martin Dürst (W3C), Mary Brady (NIST), Mick Goulish (Software AG), Mike Champion (Arbortext and Software AG), Miles Sabin (Cromwell Media), Patti Lutsky (Arbortext), Paul Grosso (Arbortext), Peter Sharpe (SoftQuad Software Inc.), Phil Karlton (Netscape), Philippe Le Hégaret (W3C, W3C team contact and Chair), Ramesh Lekshmynarayanan (Merrill Lynch), Ray Whitmer (iMall, Excite@Home, and Netscape/AOL), Rezaur Rahman (Intel), Rich Rollman (Microsoft), Rick Gessner (Netscape), Rick Jelliffe (invited), Rob Relyea (Microsoft), Scott Isaacs (Microsoft), Sharon Adler (INSO), Steve Byrne (JavaSoft), Tim Bray (invited), Tim Yu (Oracle), Tom Pixley (Netscape/AOL), Vidur Apparao (Netscape), Vinod Anupam (Lucent).

Thanks to all those who have helped to improve this specification by sending suggestions and corrections (Please, keep bugging us with your issues!).

D.1: Production Systems

This specification was written in XML. The HTML, OMG IDL, Java and ECMAScript bindings were all produced automatically.

Thanks to Joe English, author of cost, which was used as the basis for producing DOM Level 1. Thanks also to Gavin Nicol, who wrote the scripts which run on top of cost. Arnaud Le Hors and Philippe Le Hégaret maintained the scripts.

After DOM Level 1, we used Xerces as the basis DOM implementation and wish to thank the authors. Philippe Le Hégaret and Arnaud Le Hors wrote the Java programs which are the DOM application.

Thanks also to Jan Kärrman, author of html2ps, which we use in creating the PostScript version of the specification.

Glossary

Editors:: Arnaud Le Hors, W3C; Robert S. Sutor, IBM Research (for DOM Level 1)

Several of the following term definitions have been borrowed or modified from similar definitions in other W3C or standards documents. See the links within the definitions for more information.

API: An API is an Application Programming Interface, a set of functions or methods used to access some functionality.
document element: There is only one document element in a Document. This element node is a child of the Document node. See Well-Formed XML Documents in XML [XML 1.0].
document order: There is an ordering, document order, defined on all the nodes in the document corresponding to the order in which the first character of the XML representation of each node occurs in the XML representation of the document after expansion of general entities. Thus, the document element node will be the first node. Element nodes occur before their children. Thus, document order orders element nodes in order of the occurrence of their start-tag in the XML (after expansion of entities). The attribute nodes of an element occur after the element and before its children. The relative order of attribute nodes is implementation-dependent.
element: Each document contains one or more elements, the boundaries of which are either delimited by start-tags and end-tags, or, for empty elements by an empty-element tag. Each element has a type, identified by name, and may have a set of attributes. Each attribute has a name and a value. See Logical Structures in XML [XML 1.0].
logically-adjacent text nodes: Logically-adjacent text nodes are Text or CDataSection nodes that may be visited sequentially in document order without entering, exiting, or passing over Element, Comment, or ProcessingInstruction nodes.
live: An object is live if any change to the underlying document structure is reflected in the object.
model: A model is the actual data representation for the information at hand. Examples are the structural model and the style model representing the parse structure and the style information associated with a document. The model might be a tree, or a directed graph, or something else.
namespace prefix: A namespace prefix is a string that associates an element or attribute name with a namespace URI in XML. See namespace prefix in Namespaces in XML [XML Namespaces].
namespace URI: A namespace URI is a URI that identifies an XML namespace. This is called the namespace name in Namespaces in XML [XML Namespaces].
read only node: A read only node is a node that is immutable. This means its list of children, its content, and its attributes, when it is an element, cannot be changed in any way. However, a read only node can possibly be moved, when it is not itself contained in a read only node.
tokenized: The description given to various information items (for example, attribute values of various types, but not including the StringType CDATA) after having been processed by the XML processor. The process includes stripping leading and trailing white space, and replacing multiple space characters by one. See the definition of tokenized type.
well-formed document: A document is well-formed if it is tag valid and entities are limited to single elements (i.e., single sub-trees).

References

For the latest version of any W3C specification please consult the list of W3C Technical Reports available at http://www.w3.org/TR.

F.1: Normative references

DOM Level 3 Core: W3C (World Wide Web Consortium) Document Object Model Level 3 Core Specification, September 2001. Available at http://www.w3.org/TR/DOM-Level-3-Core
ECMAScript: ISO (International Organization for Standardization). ISO/IEC 16262:1998. ECMAScript Language Specification. Available from ECMA (European Computer Manufacturers Association) at http://www.ecma.ch/ecma1/STAND/ECMA-262.HTM
Java: Sun Microsystems Inc. The Java Language Specification, James Gosling, Bill Joy, and Guy Steele, September 1996. Available at http://java.sun.com/docs/books/jls
OMGIDL: OMG (Object Management Group) IDL (Interface Definition Language) defined in The Common Object Request Broker: Architecture and Specification, version 2.3.1, October 1999. Available from http://www.omg.org
XML Information set: W3C (World Wide Web Consortium) XML Information Set, October 2001. Available at http://www.w3.org/TR/2001/REC-xml-infoset-20011024
XPath 1.0: W3C (World Wide Web Consortium) XML Path Language (XPath) Version 1.0, November 1999. Available at http://www.w3.org/TR/1999/REC-xpath-19991116

F.2: Informative references

XML 1.0: W3C (World Wide Web Consortium) Extensible Markup Language (XML) 1.0, October 2000. Available at http://www.w3.org/TR/2000/REC-xml-20001006
XML Namespaces: W3C (World Wide Web Consortium) Namespaces in XML, January 1999. Available at http://www.w3.org/TR/1999/REC-xml-names-19990114

Document Object Model (DOM) Level 3 XPath Specification

Version 1.0

W3C Working Draft 08 February 2002

Abstract

Status of this document

Table of contents

Expanded Table of Contents

Copyright Notice

W3C Document Copyright Notice and License

W3C Software Copyright Notice and License

1. Document Object Model XPath

Table of contents

1.1. Introduction

1.2. Mapping DOM to XPath

1.2.1. Text Nodes

1.2.2. Namespace Nodes

1.2.3. Document order

1.3. Interfaces

Appendix A: IDL Definitions

xpath.idl:

Appendix B: Java Language Binding

B.1: Other XPath interfaces

org/w3c/dom/xpath/XPathException.java:

org/w3c/dom/xpath/XPathEvaluator.java:

org/w3c/dom/xpath/XPathExpression.java:

org/w3c/dom/xpath/XPathNSResolver.java:

org/w3c/dom/xpath/XPathResult.java:

org/w3c/dom/xpath/XPathNamespace.java:

Appendix C: ECMAScript Language Binding

Appendix D: Acknowledgements

D.1: Production Systems

Glossary

References

F.1: Normative references

F.2: Informative references

Index

ANY_TYPE	ANY_UNORDERED_NODE_TYPE	API 1, 2

BOOLEAN_TYPE	booleanValue

createExpression	createNSResolver

document element	document order 1, 2	DOM Level 3 Core 1, 2, 3, 4

ECMAScript	element 1, 2, 3	evaluate 1, 2

FIRST_ORDERED_NODE_TYPE

INVALID_EXPRESSION_ERR	invalidIteratorState	iterateNext

Java

live 1, 2	logically-adjacent text nodes 1, 2	lookupNamespaceURI

model 1, 2

namespace prefix 1, 2, 3, 4	namespace URI 1, 2, 3, 4	NUMBER_TYPE
numberValue

OMGIDL	ORDERED_NODE_ITERATOR_TYPE	ORDERED_NODE_SNAPSHOT_TYPE
ownerElement

read only node 1, 2	resultType

singleNodeValue	snapshotItem	snapshotLength
STRING_TYPE	stringValue

tokenized	TYPE_ERR

UNORDERED_NODE_ITERATOR_TYPE	UNORDERED_NODE_SNAPSHOT_TYPE

well-formed document

XML 1.0 1, 2, 3	XML Information set 1, 2	XML Namespaces 1, 2, 3
XPath 1.0 1, 2, 3	XPATH_NAMESPACE_NODE	XPathEvaluator
XPathException	XPathExpression	XPathNamespace
XPathNSResolver	XPathResult