1. Document Object Model Events

1.1.1 Event flows

This document specifies an event flow for tree-based structures: DOM event flow. While it is expected that HTML and XML applications will follow this event flow, applications might reuse the interfaces defined in this document for non tree-based structures. In that case, it is the responsibility of such applications to define their event flow and how it relates to the DOM event flow. An example of such use can be found in [DOM Level 3 Load and Save].

1.1.2 Conformance

An implementation is DOM Level 3 Events conformant if it supports the Core module defined in [DOM Level 2 Core], the DOM event flow and the interfaces with their associated semantics defined in Basic interfaces. An implementation conforms to a DOM Level 3 Events module if it conforms to DOM Level 3 Events and the event types defined in the module. An implementation conforms to an event type if it conforms to its associated semantics and DOM interfaces. For example, an implementation conforms to the DOM Level 3 User Interface Events module (see User Interface event types) if it conforms to DOM Level 3 Events (i.e. implements all the basic interfaces), can generate the event types {"http://www.w3.org/2001/xml-events", "DOMActivate"} {"http://www.w3.org/2001/xml-events", "DOMFocusIn"} {"http://www.w3.org/2001/xml-events", "DOMFocusOut"} accordingly to their semantics, supports the UIEvent interface, and conforms to the DOM Level 2 Core module.

Note: An implementation which does not conform to an event module can still implement the DOM interfaces associated with it. The DOM application can then create an event object using the DocumentEvent.createEvent() method and dispatch an event type associated with this interface using the EventTarget.dispatchEvent() method.

A DOM application may use the hasFeature(feature, version) method of the DOMImplementation interface with parameter values "Events" and "3.0" (respectively) to determine whether or not DOM Level 3 Events is supported by the implementation. In order to fully support DOM Level 3 Events, an implementation must also support the "Core" feature defined in the DOM Level 2 Core specification [DOM Level 2 Core] and use the DOM event flow. For additional information about conformance, please see the DOM Level 3 Core specification [DOM Level 3 Core]. DOM Level 3 Events is built on top of DOM Level 2 Events [DOM Level 2 Events], i.e. a DOM Level 3 Events implementation where hasFeature("Events", "3.0") returns true must also return true when the version number is "2.0", "" or, null.

Each event module describes its own feature string in the event module listing.

1.2.1 Phases

The event is dispatched following a path from the root of the tree to this target node. It can then be handled locally at the target node level or from any target's ancestors higher in the tree. The event dispatching (also called event propagation) occurs in three phases and the following order:

1. The capture phase: the event is dispatched to the target's ancestors from the root of the tree to the direct parent of the target node.
2. The target phase: the event is dispatched to the target node.
3. The bubbling phase: the event is dispatched to the target's ancestors from the direct parent of the target node to the root of the tree.

Figure: graphical representation of an event dispatched in a DOM tree using the DOM event flow [SVG 1.0 version]

Note: An SVG 1.0 version of the representation above is also available.

The target's ancestors are determined before the initial dispatch of the event. If the target node is removed during the dispatching, or a target's ancestor is added or removed, the event propagation will always be based on the target node and the target's ancestors determined before the dispatch.

Some events may not necessarily accomplish the three phases of the DOM event flow, e.g. the event could only be defined for one or two phases. As an example, events defined in this specification will always accomplish the capture and target phases but some will not accomplish the bubbling phase ("bubbling events" versus "non-bubbling events", see also the Event.bubbles attribute).

1.2.2 Event listeners

Each node encountered during the dispatch of the event may contain event listeners.

1.4.1 Event types and event categories

An event type could be part of one or more categories. A category is represented using a local name and a namespace URI as defined in [XML Namespaces]. The event types defined in this specification are not associated with one or more event categories and this specification does not provide methods to associate them. Other specifications may create and associate event categories with event listeners but in such case would need to inform the dispatch mechanism of those event categories. An example of the use of categories is given at Using VoiceXML Events.

1.4.2 Complete list of event types

Depending on the level of DOM support, or the devices used for display (e.g. screen) or interaction (e.g. mouse, keyboard, touch screen, voice, ...), these event types can be generated by the implementation. When used with an [XML 1.0] or [HTML 4.01] application, the specifications of those languages may restrict the semantics and scope (in particular the possible target nodes) associated with an event type. For example, {"http://www.w3.org/2001/xml-events", "click"} can be targeted to all [XHTML 1.0] elements except applet, base, basefont, bdo, br, font, frame, frameset, head, html, iframe, isindex, meta, param, script, style, and title. Refer to the specification defining the language used in order to find those restrictions or to find event types that are not defined in this document.

The following list defines all event types (with the exception of two event types preserved for backward compatibility with [HTML 4.01], see HTML Events) provided in this specification. All event types defined in this specification are bound to the namespace URI "http://www.w3.org/2001/xml-events" and the following list only enumerates the local name of the event type.

DOMActivate

An element is activated, for instance, using a mouse device, a keyboard device, or a voice command.

Note: The activation of an element is device dependent but is also application dependent, e.g. a link in a document can be activated using a mouse click or a mouse double click.

DOMFocusIn

An event target receives focus, for instance via a pointing device being moved onto an element or using keyboard navigation. The focus is given to the element before the dispatch of this event type.

DOMFocusOut

A event target loses focus, for instance via a pointing device being moved out of an element or by tabbing navigation out of the element. The focus is taken from the element before the dispatch of this event type.

textInput

One or more characters have been entered. The characters can originate from a variety of sources. For example, it could be characters resulting from a key being pressed or released on a keyboard device, characters resulting from the processing of an input method editor, or resulting from a voice command. Where a "paste" operation generates a simple sequence of characters, i.e. a text without any structure or style information, this event type should be generated as well.

click

A pointing device button is clicked over an element. The definition of a click depends on the environment configuration; i.e. may depend on the screen location or the delay between the press and release of the pointing device button. In any case, the target node must be the same between the mousedown, mouseup, and click. The sequence of these events is: {"http://www.w3.org/2001/xml-events", "mousedown"}, {"http://www.w3.org/2001/xml-events", "mouseup"}, and {"http://www.w3.org/2001/xml-events", "click"}. Note that, given the definition of a click, If one or more of the event types {"http://www.w3.org/2001/xml-events", "mouseover"}, {"http://www.w3.org/2001/xml-events", "mousemove"}, and {"http://www.w3.org/2001/xml-events", "mouseout"} occur between the press and release of the pointing device button, the event type {"http://www.w3.org/2001/xml-events", "click"} cannot occur. In the case of nested elements, this event type is always targeted at the most deeply nested element.

mousedown

A pointing device button is pressed over an element. In the case of nested elements, this event type is always targeted at the most deeply nested element.

mouseup

A pointing device button is released over an element. In the case of nested elements, this event type is always targeted at the most deeply nested element.

mouseover

A pointing device is moved onto an element. In the case of nested elements, this event type is always targeted at the most deeply nested element.

mousemove

A pointing device is moved while it is over an element. In the case of nested elements, this event type is always targeted at the most deeply nested element.

mouseout

A pointing device is moved away from an element. In the case of nested elements, this event type is always targeted at the most deeply nested element.

keydown

A key is pressed down. This event type is device dependent and relies on the capabilities of the input devices and how they are mapped in the operating system. This event type is generated after the keyboard mapping but before the processing of an input method editor. This event should logically happen before the event {"http://www.w3.org/2001/xml-events", "keyup"} is produced. Whether a keydown contributes or not to the generation of a text event is implementation dependent.

keyup

A key is released. This event type is device dependent and relies on the capabilities of the input devices and how they are mapped in the operating system. This event type is generated after the keyboard mapping but before the processing of an input method editor. This event should logically happen after the event {"http://www.w3.org/2001/xml-events", "keydown"} is produced. Whether a keyup contributes or not to the generation of a text event is implementation dependent.

DOMSubtreeModified

This is a general event for notification of all changes to the document. It can be used instead of the more specific events listed below. It may be dispatched after a single modification to the document or, at the implementation's discretion, after multiple changes have occurred. The latter use should generally be used to accommodate multiple changes which occur either simultaneously or in rapid succession. The target of this event is the lowest common parent of the changes which have taken place. This event is dispatched after any other events caused by the mutation(s) have occurred.

DOMNodeInserted

A node has been added as a child of another node. This event is dispatched after the insertion has taken place. The target node of this event is the node being inserted.

DOMNodeRemoved

A node is being removed from its parent node. This event is dispatched before the node is removed from the tree. The target node of this event is the node being removed.

DOMNodeRemovedFromDocument

A node is being removed from a document, either through direct removal of the node or removal of a subtree in which it is contained. This event is dispatched before the removal takes place. The target node of this event type is the node being removed. If the node is being directly removed, the event type {"http://www.w3.org/2001/xml-events", "DOMNodeRemoved"} will fire before this event type.

DOMNodeInsertedIntoDocument

A node is being inserted into a document, either through direct insertion of the node or insertion of a subtree in which it is contained. This event is dispatched after the insertion has taken place. The target node of this event is the node being inserted. If the node is being directly inserted, the event type {"http://www.w3.org/2001/xml-events", "DOMNodeInserted"} will fire before this event type.

DOMAttrModified

Occurs after an Attr has been modified on a node. The target node of this event is the parent Element node whose Attr changed. It is expected that string based replacement of an Attr value will be viewed as a modification of the Attr since its identity does not change. Subsequently replacement of the Attr node with a different Attr node is viewed as the removal of the first Attr node and the addition of the second.

DOMCharacterDataModified

Occurs after CharacterData.data or ProcessingInstruction.data have been modified but the node itself has not been inserted or deleted. The target node of this event is the CharacterData node or the ProcessingInstruction node.

DOMElementNameChanged

Occurs after the namespaceURI and/or the nodeName of an Element node have been modified (e.g., the element was renamed using Document.renameNode()). The target of this event is the renamed Element node.

DOMAttributeNameChanged

Occurs after the namespaceURI and/or the nodeName of a Attr node have been modified (e.g., the attribute was renamed using Document.renameNode). The target of this event is the parent Element node whose Attr has been renamed.

load

The DOM Implementation finishes loading the resource (such as the document) and any dependent resources (such as images, style sheets, or scripts). Dependent resources that fail to load will not prevent this event from firing if the resource that loaded them is still accessible via the DOM. If this event type is dispatched, implementations are required to dispatch this event at least on the Document node.

unload

The DOM implementation removes from the environment the resource (such as the document) or any dependent resources (such as images, style sheets, scripts). The document is unloaded after the dispatch of this event type. If this event type is dispatched, implementations are required to dispatch this event at least on the Document node.

abort

The loading of the document, or a resource linked from it, is stopped before being entirely loaded.

error

The document, or a resource linked from it, has been loaded but cannot be interpreted according to its semantic, such as an invalid image, a script execution error, or non-well-formed XML.

select

A user selects some text. DOM Level 3 Events does not provide contextual information to access the selected text. The selection occured before the dispatch of this event type.

change

A control loses the input focus and its value has been modified since gaining focus.

submit

A form, such as [HTML 4.01], [XHTML 1.0], or [XForms 1.0] form, is submitted.

reset

A form, such as [HTML 4.01], [XHTML 1.0], or [XForms 1.0] form, is reset.

resize

A document view or an element has been resized. The resize occured before the dispatch of this event type.

scroll

A document view or an element has been scrolled. The scroll occured before the dispatch of this event type.

The following table provides additional information on the event types. All events will accomplish the capture and target phases, but not all of them will accomplish the bubbling phase (see also DOM event flow). Some events are not cancelable (see Default actions and cancelable events). Some events will only be dispatched to a specific set of possible targets, specified using node types. Contextual information related to the event type is accessible using DOM interfaces.

As an example, the event {"http://www.w3.org/2001/xml-events", "load"} will trigger event listeners attached on Element nodes for that event and on the capture and target phases. This event cannot be cancelled. If an event listener for the load event is attached to a node other than Element nodes, or if it is attached to the bubbling phase only, this event listener cannot be triggered.

The event objects associated with the event types described above may contain context information. Refer to the description of the DOM interfaces for further information.

1.4.3 Compatibility with DOM Level 2 Events

Namespace URIs were only introduced in DOM Level 3 Events and were not part of DOM Level 2 Events. DOM Level 2 Events methods are namespace ignorant and the event type is only represented by an XML name, specified in the Event.type attribute.

Therefore, while it is safe to use these methods when not dealing with namespaces, using them and the new ones at the same time should be avoided. DOM Level 2 Events methods solely identify events by their Event.type. On the contrary, the namespaces aware DOM Level 3 Events methods, identify attribute nodes by their Event.namespaceURI and Event.type. Because of this fundamental difference, mixing both sets of methods can lead to unpredictable results. For example, using EventTarget.addEventListenerNS(namespaceURI, type, listener, ...), two event listeners (or more) could be registered using the same type and same useCapture values, but different namespaceURIs. Calling EventTarget.removeEventListener(type, listener, ...) with that type and useCapture could then remove any or none of those event listeners. The result depends on the implementation. The only guarantee in such cases is that all methods which access an event listener by its namespaceURI and type will access the same event listener. For instance, EventTarget.removeEventListenerNS(namespaceURI, type, listener, ...) removes the event that EventTarget.addEventListenerNS(namespaceURI, type, listener, ...) added.

For compatibility reasons, the dispatching of an event will ignore namespace URIs if either the event or the event listener has a null namespace URI. If a DOM Level 2 event (i.e. with a null namespace URI) is dispatched in the DOM tree, all event listeners that match the type will be triggered as described in the DOM event flow. If a DOM Level 3 event (i.e. with a namespace URI) is dispatched in the DOM tree, all event listeners with the same type and the same or null namespace URI will be triggered as described in the DOM event flow.

1.5.1 Using the EventTarget methods

The user can attach an event listener using the methods on the EventTarget interface:

myCircle.addEventListenerNS("http://www.w3.org/2001/xml-events",
                            "DOMActivate",
                            myListener,
                            true,
                            null);

The methods do not provide the ability to register the same event listener more than once for the same event type and the same phase. It is not possible to register an event listener:

• for only one of the target and bubbling phases since those phases are coupled during the registration (but the listener itself could ignore events during one of these phases if desired).
• for a specific event category.

To register an event listener, DOM applications must use the methods EventTarget.addEventListener() and EventTarget.addEventListenerNS().

An EventListener being registered on an EventTarget may choose to have that EventListener triggered during the capture phase by specifying the useCapture parameter of the EventTarget.addEventListener() or EventTarget.addEventListenerNS() methods to be true. If false, the EventListener will be triggered during the target and bubbling phases.

1.5.2 Using XML Events

In [XML Events], event listeners are attached using elements and attributes:

<listener event="DOMActivate" observer="myCircle" handler="#myListener"
          phase="capture" propagate="stop"/>

Event listeners can only be registered on Element nodes, i.e. other Node types are not addressable, and cannot be registered for a specific group either, i.e. they are always attached to the default group. The target phase and the bubbling phase are coupled during the registration. [XML Events] does not address namespaces in event types. If the value of the event attribute of the listener element contains a colon (':'), it should be interpreted as a QName as defined in [XML Schema Part 2].

1.5.3 Using VoiceXML Events

In [VoiceXML 2.0], event listeners are attached using elements:

<form>
  <field>
    <prompt>Please say something</prompt>
    <catch event="error.noauthorization">
     <prompt>You don't have the authorization!</prompt>
    </catch>
    <catch event="connection.disconnect.hangup">
     <prompt>Connection error</prompt>
    </catch>
    <catch event="connection.disconnect">
     <prompt>Connection error</prompt>
    </catch>
  </field>
  <catch event="error">
    <prompt>Unknown error</prompt>
  </catch>
</form>

Event listeners can only be registered on Element nodes, i.e. other Node types are not addressable, and cannot be registered for a specific group either, i.e. they are always attached to the default group. The target phase and the bubbling phase are coupled during the registration. [VoiceXML 2.0] does not address namespaces in event types but uses the notion of event categories. The event type "connection.disconnect.hangup" could be associated to the event categories {"http://www.example.org/2003/voicexml", "connection"} and {"http://www.example.org/2003/voicexml", "connection.disconnect"}.

1.5.4 Using XML or HTML attributes

In languages such as [HTML 4.01], [XHTML 1.0], or [SVG 1.1], event listeners are specified as attributes:

<circle id="myCircle" onactivate="myListener(evt)"
        cx="300" cy="225" r="100" fill="red"/>

Since only one attribute with the same name can appear on an element, it is therefore not possible to register more than one event listener on a single EventTarget for the event type. Also, event listeners can only be registered on Element nodes for the target phase and bubbling phase, i.e. other Node types and the capture phase are not addressable with these languages. Event listeners cannot be registered for a specific group either, i.e. they are always attached to the default group.

In order to achieve compatibility with those languages, implementors may view the setting of attributes which represent event handlers as the creation and registration of an EventListener on the EventTarget. The value of useCapture defaults to false. This EventListener behaves in the same manner as any other EventListeners which may be registered on the EventTarget. If the attribute representing the event listener is changed, this may be viewed as the removal of the previously registered EventListener and the registration of a new one. Furthermore, no specification is made as to the order in which event attributes will receive the event with regards to the other EventListeners on the EventTarget.

1.6.1 Event creation

In most cases, the events dispatched by the DOM Events implementation are also created by the implementation. It is however possible to simulate events such as mouse events by creating the Event objects and dispatch them using the DOM Events implementation.

DOM Events provides two ways for creating Event objects. An application can either create Event objects that are known to the implementation, or create its own objects and have them dispatched by the DOM Events implementation.

Creating Event objects that are known to the DOM Events implementation is done using DocumentEvent.createEvent(). The application must then initialize the object by calling the appropriate initialization method before invoking EventTarget.dispatchEvent(). The Event objects created must be known by the DOM Events implementation; otherwise an event exception is thrown.

The DOM application might want to create its own Event objects, in order to change the default Event implementation provided by the DOM Events implementation or to generate new event types with specific contextual information. In any case, the application is responsible for creating and initializing the Event object. The application can then dispatch the event using the DOM Events implementation by using EventTarget.dispatchEvent().

However, the DOM Events implementation requires to have access to two attributes in the Event object in order to accomplish the dispatch appropriately: Event.currentTarget and Event.eventPhase. Those attributes are defined as readonly in the Event interface since event listeners must not change them and it is the responsibility of the DOM Events implementation to update them during the event flow. Therefore, implementing the Event interface when creating its own events is not enough for an application since the DOM Events implementation will not be able to update the current phase and the current node during the dispatch, unless the event object also implements the CustomEvent interface to give access to the relevant attributes.

Interface DocumentEvent (introduced in DOM Level 2)

The DocumentEvent interface provides a mechanism by which the user can create an Event object of a type supported by the implementation. If the feature "Events" is supported by the Document object, the DocumentEvent interface must be implemented on the same object. If the feature "+Events" is supported by the Document object, an object that supports the DocumentEvent interface must be returned by invoking the method Node.getFeature("+Events", "3.0") on the Document object.

IDL Definition

// Introduced in DOM Level 2:
interface DocumentEvent {
  Event              createEvent(in DOMString eventType)
                                        raises(DOMException);
  // Introduced in DOM Level 3:
  boolean            canDispatch(in DOMString namespaceURI, 
                                 in DOMString type);
};

Methods

canDispatch introduced in DOM Level 3

Test if the implementation can generate events of a specified type.

Parameters

namespaceURI of type DOMString

Specifies the Event.namespaceURI of the event.

type of type DOMString

Specifies the Event.type of the event.

Return Value

boolean

true if the implementation can generate and dispatch this event type, false otherwise.

No Exceptions

createEvent

Parameters

eventType of type DOMString

The eventType parameter specifies the name of the DOM Events interface to be supported by the created event object, e.g. "Event", "MouseEvent", "MutationEvent" and so on. If the Event is to be dispatched via the EventTarget.dispatchEvent() method the appropriate event init method must be called after creation in order to initialize the Event's values.
As an example, a user wishing to synthesize some kind of UIEvent would invoke DocumentEvent.createEvent("UIEvent"). The UIEvent.initUIEventNS() method could then be called on the newly created UIEvent object to set the specific type of user interface event to be dispatched, {"http://www.w3.org/2001/xml-events", "DOMActivate"} for example, and set its context information, e.g. UIEvent.detail in this example.
The createEvent method is used in creating Events when it is either inconvenient or unnecessary for the user to create an Event themselves. In cases where the implementation provided Event is insufficient, users may supply their own Event implementations for use with the EventTarget.dispatchEvent() method. However, the DOM implementation needs access to the attributes Event.currentTarget and Event.eventPhase to appropriately propagate the event in the DOM tree. Therefore users' Event implementations might need to support the CustomEvent interface for that effect.

Note: For backward compatibility reason, "UIEvents", "MouseEvents", "MutationEvents", and "HTMLEvents" feature names are valid values for the parameter eventType and represent respectively the interfaces "UIEvent", "MouseEvent", "MutationEvent", and "Event".

Return Value

Event

The newly created event object.

Exceptions

DOMException

NOT_SUPPORTED_ERR: Raised if the implementation does not support the Event interface requested.

Interface CustomEvent (introduced in DOM Level 3)

The CustomEvent interface gives access to the attributes Event.currentTarget and Event.eventPhase. It is intended to be used by the DOM Events implementation to access the underlying current target and event phase while dispatching a custom Event in the tree; it is also intended to be implemented, and not used, by DOM applications.

The methods contained in this interface are not intended to be used by a DOM application, especially during the dispatch on the Event object. Changing the current target or the current phase may result in unpredictable results of the event flow. The DOM Events implementation should ensure that both methods return the appropriate current target and phase before invoking each event listener on the current target to protect DOM applications from malicious event listeners.

Note: If this interface is supported by the event object, Event.isCustom() must return true.

IDL Definition

// Introduced in DOM Level 3:
interface CustomEvent : Event {
  void               setDispatchState(in EventTarget target, 
                                      in unsigned short phase);
  boolean            isPropagationStopped();
  boolean            isImmediatePropagationStopped();
};

Methods

isImmediatePropagationStopped

The isImmediatePropagationStopped method is used by the DOM Events implementation to know if the method stopImmediatePropagation() has been called for this event. It returns true if the method has been called, false otherwise.

Return Value

boolean

true if the event propagation has been stopped immediately in the current group.

No Parameters

No Exceptions

isPropagationStopped

This method will return true if the method stopPropagation() has been called for this event, false in any other cases.

Return Value

boolean

true if the event propagation has been stopped in the current group.

No Parameters

No Exceptions

setDispatchState

The setDispatchState method is used by the DOM Events implementation to set the values of Event.currentTarget and Event.eventPhase. It also reset the states of isPropagationStopped and isImmediatePropagationStopped.

Parameters

target of type EventTarget

Specifies the new value for the Event.currentTarget attribute.

phase of type unsigned short

Specifies the new value for the Event.eventPhase attribute.

No Return Value

No Exceptions

1.7.1 User Interface event types

The User Interface event module contains basic event types associated with user interfaces.

Interface UIEvent (introduced in DOM Level 2)

The UIEvent interface provides specific contextual information associated with User Interface events.

To create an instance of the UIEvent interface, use the DocumentEvent.createEvent("UIEvent") method call.

IDL Definition

// Introduced in DOM Level 2:
interface UIEvent : Event {
  readonly attribute views::AbstractView view;
  readonly attribute long            detail;
  void               initUIEvent(in DOMString typeArg, 
                                 in boolean canBubbleArg, 
                                 in boolean cancelableArg, 
                                 in views::AbstractView viewArg, 
                                 in long detailArg);
  // Introduced in DOM Level 3:
  void               initUIEventNS(in DOMString namespaceURI, 
                                   in DOMString typeArg, 
                                   in boolean canBubbleArg, 
                                   in boolean cancelableArg, 
                                   in views::AbstractView viewArg, 
                                   in long detailArg);
};

Attributes

detail of type long, readonly

Specifies some detail information about the Event, depending on the type of event.

view of type views::AbstractView, readonly

The view attribute identifies the AbstractView from which the event was generated.

Methods

initUIEvent

The initUIEvent method is used to initialize the value of a UIEvent object and has the same behavior as Event.initEvent().

Parameters

typeArg of type DOMString

Refer to the Event.initEvent() method for a description of this parameter.

canBubbleArg of type boolean

Refer to the Event.initEvent() method for a description of this parameter.

cancelableArg of type boolean

Refer to the Event.initEvent() method for a description of this parameter.

viewArg of type views::AbstractView

Specifies UIEvent.view.

detailArg of type long

Specifies UIEvent.detail.

No Return Value

No Exceptions

initUIEventNS introduced in DOM Level 3

The initUIEventNS method is used to initialize the value of a UIEvent object and has the same behavior as Event.initEventNS().

Parameters

namespaceURI of type DOMString

Refer to the Event.initEventNS() method for a description of this parameter.

typeArg of type DOMString

Refer to the Event.initEventNS() method for a description of this parameter.

canBubbleArg of type boolean

Refer to the Event.initEventNS() method for a description of this parameter.

cancelableArg of type boolean

Refer to the Event.initEventNS() method for a descriptio