User Interface Independence for Accessible Rich Internet Applications

1.1. Feature Implementation

The authors anticipate that this proposal will not be published as a standalone W3C Recommendation. Instead, the authors request that the features proposed in this document be integrated, as appropriate, into the specifications for HTML 5, DOM Level 3, and/or ARIA 2.

1.2. Problem Description

At the time of this writing, the current draft of WAI-ARIA states that:

Accessibility of web content requires semantic information about widgets, structures, and behaviors, in order to allow assistive technologies to convey appropriate information to persons with disabilities. [The WAI-ARIA] specification provides an ontology of roles, states, and properties that define accessible user interface elements and can be used to improve the accessibility and interoperability of web content and applications. These semantics are designed to allow an author to properly convey user interface behaviors and structural information to assistive technologies in document-level markup.

The WAI-ARIA 1.0 draft specifies an adequate and standardized means for web applications to convey accessibility semantics through declarative markup in the DOM. However, there is currently no standardized, robust means for assistive technology to assume control of customized user interface widgets, or convey the user's intent for control of the web application. Simple control over web applications can be achieved by using standard activation events, like click or DOMActivate, but full control over secondary actions (tree expansion, grid sorting, scrolling) can only be achieved by using a set of keyboard shortcuts promoted by a group outside the W3C WAI calling itself the DHTML Style Guide Working Group. The style guide recommends authors register for all key events and listen, for example, for Control+Shift+M to open a popup menu during a drag and drop operation.

While we appreciate the efforts of the DHTML Style Guide Working Group, we feel that user interface should be controlled by operating systems, and not defined as part of any technical specification. We also believe that there are many serious problems with the DHTML Style Guide, including the following items:

• Adoption: Implementing complex behavior in ARIA 1.0 widgets requires that the web application authors adopt this set of keyboard commands, which may have been a reasonable requirement, except that it also requires all users of assistive technology to learn these commands in addition to their existing assistive technology interface, and understand that these commands will only behave as expected on a small minority of web applications that have adopted the DHTML Style Guide approach.
• Localization: Web standards are intended for a global audience, and specific keyboard shortcuts, like Control+Shift+M, cannot be required for certain localizations. For example, not all keyboards have Control, Shift, or M keys, and even if they did, the mnemonic logic that "M opens a menu" does not apply in most languages.
• Operating system independence: The DHTML Style Guide takes a Windows-centric approach, where the Control key is used as the primary modifier key. Other operating systems may have different primary modifier keys, such as the Command key on Mac OS X, and recommending an OS-centric set of keyboard shortcuts adds additional burden on the end user, web application author, or both.
• User interface independence: Perhaps the most serious flaw in the assumption of control via keyboard shortcuts is that not all devices have a keyboard. Touch screen devices, or speech-controlled assistive technologies, for example, would be forced to simulate specific keypress events on all web pages, in the unlikely event that the web author might have registered for these events.

For these reasons and others, we believe adoption of complex behavior in ARIA 1.0 widgets will be slow for any control that cannot be activated with a single, easy-to-learn, easy-to-remember, localization-independent keystroke like arrow keys, PageUp, PageDown, Home, End, Spacebar, Enter, Delete, Escape, etc. We also believe that the keyboard shortcuts recommended in the DHTML Style Guide should only be used as a temporary stop-gap measure. The authors wish to encourage the HTML, DOM, and PF Working Groups to provide a standardized solution with the utmost expedience.

It is in this interest that we offer the following proposal, which we believe solves the aforementioned problems. The proposal is organized into three parts: UI Change Request Events for all user agents, Accessibility Events for assistive technology, and additions to the Navigator interface for Assistive Technology Identification and Notification.

Interface UIRequestEvent

interface UIRequestEvent : UIEvent {
  
  // UA or AT notifies web app of a change request
  const unsigned short    UNDO    =  1;
  const unsigned short    REDO    =  2;
  const unsigned short    CANCEL  =  3;
  const unsigned short    DELETE  =  4;
  // expect more type constants will be added for other event types…
  // ZOOM_IN / ZOOM_OUT ? perhaps that should just be slider widget, covered under ValueChangeRequest
  
  readonly attribute unsigned short    eventType;
  
  void initUIRequestEvent(
         in DOMString typeArg,
         in boolean canBubbleArg,
         in boolean cancelableArg,
         in views::AbstractView viewArg,
         in long detailArg,
         in unsigned short eventTypeArg
       );
};

The different types of UIRequestEvents that can occur are:

UndoRequest

Initiated when the user agent or assistive technology sends an 'undo' request to the web application.

• Bubbles: Yes
• Cancelable: Yes
• Context Info: eventType

RedoRequest

Initiated when the user agent or assistive technology sends a 'redo' request to the web application.

• Bubbles: Yes
• Cancelable: Yes
• Context Info: eventType

EscapeRequest

Initiated when the user agent or assistive technology sends a 'escape' request to the web application.

• Bubbles: Yes
• Cancelable: Yes
• Context Info: eventType

DeleteRequest

Initiated when the user agent or assistive technology sends a 'delete' request to the web application.

• Bubbles: Yes
• Cancelable: Yes
• Context Info: eventType

Interface UIScrollRequestEvent

interface UIScrollRequestEvent : UIRequestEvent {
  
  // for custom scroll views or widgets (e.g. carousels, lists, grids)
  const unsigned short    LEFT          =  1;
  const unsigned short    UP            =  2;
  const unsigned short    RIGHT         =  3;
  const unsigned short    DOWN          =  4;
  const unsigned short    LEFT_LIMIT    =  5;
  const unsigned short    TOP_LIMIT     =  6;
  const unsigned short    RIGHT_LIMIT   =  7;
  const unsigned short    BOTTOM_LIMIT  =  8;
  
  readonly attribute unsigned short   scrollType;
  
  void initUIScrollRequestEvent(
         in DOMString typeArg,
         in boolean canBubbleArg,
         in boolean cancelableArg,
         in views::AbstractView viewArg,
         in long detailArg,
         in unsigned short eventTypeArg
         in unsigned short scrollTypeArg
       );
};

The single type of UIScrollRequestEvent that can occur is:

ScrollRequest

Initiated when the user agent or assistive technology sends a scroll request to the web application. Scroll events need only be used on custom scroll views (lists and grids showing data subsets, carousels, etc.), as user agents and assistive technologies already manage scrolling of native scroll views.

Note: The scroll type constants are more or less equivalent to expected behavior for PageUp/PageDown and Home/End keys on native scroll views, but also allow horizontal scrolling.

• Bubbles: Yes
• Cancelable: Yes
• Context Info: scrollType

Interface UIValueChangeRequestEvent

interface UIValueChangeRequestEvent : UIRequestEvent {
  
  // value changes (e.g. ranges)
  const unsigned short    INCREMENT        =  1;
  const unsigned short    INCREMENT_SMALL  =  2;
  const unsigned short    INCREMENT_LARGE  =  3;
  const unsigned short    INCREMENT_MAX    =  4;
  const unsigned short    DECREMENT        =  5;
  const unsigned short    DECREMENT_SMALL  =  6;
  const unsigned short    DECREMENT_LARGE  =  7;
  const unsigned short    DECREMENT_MIN    =  8;
  
  readonly attribute unsigned short   changeType;
  
  void initUIValueChangeRequestEvent(
         in DOMString typeArg,
         in boolean canBubbleArg,
         in boolean cancelableArg,
         in views::AbstractView viewArg,
         in long detailArg,
         in unsigned short eventTypeArg,
         in unsigned short changeTypeArg
       );
};

The single type of UIValueChangeRequestEvent that can occur is:

ValueChangeRequest

Initiated when the user agent or assistive technology sends a value change request to the web application.

Web authors should code applications to accept all values of the changeType argument. For example, if there is no special behavior for INCREMENT_SMALL or INCREMENT_LARGE, web applications would behave as if they had received a basic INCREMENT change type.

• Bubbles: Yes
• Cancelable: Yes
• Context Info: eventType

Example

Users, wanting to change the value of a custom range widget (slider, media progressbar, etc.) in a web application, can indicate their intent a number of ways, including pressing various keys (Up, Down, Left, Right, PageUp, PageDown, Home, End) on most keyboard-controlled interfaces, and through gestures on many touch-enabled interfaces. User agents understanding this intent should initiate a ValueChangeRequest event. Web authors who have registered for this event, should process the event to determine whether to cancel the event. If the value change action is understood in the context of the web application, web authors should change the value of the associated widget by an amount determined via the changeType argument, and cancel the event using the event object's preventDefault() method. If the event is not cancelled by the web author, user agents may pass the literal interaction event to the web application; in this case, in the form of a keypress or touch event.

Interface DOMAttributeChangeRequestEvent

interface DOMAttributeChangeRequestEvent : UIRequestEvent {
  
  readonly attribute DOMString    attrName;
  readonly attribute DOMString    newValue;
  
  void initDOMAttributeChangeRequestEvent(
         in DOMString typeArg,
         in boolean canBubbleArg,
         in boolean cancelableArg,
         in views::AbstractView viewArg,
         in long detailArg,
         in unsigned short eventTypeArg,
         in DOMString attrNameArg,
         in DOMString newValueArg
       );
};

The single type of DOMAttributeChangeRequestEvent that can occur is:

DOMAttrChangeRequest

Initiated when the user agent or assistive technology sends an attribute change request to the web application. In order for web applications to understand the intent of change request events from the user agent or assistive technology, these change requests should be limited to attributes for which a change in value indicates a discrete, defined action for known types of widgets and UI elements.

Note: Currently, this limitation indicates that DOMAttrChangeRequest only applies to WAI-ARIA widgets, but it has the potential to be used with future iterations of HTML5 or SVG.

• Bubbles: Yes
• Cancelable: Yes
• Context Info: attrName, newValue

Interface AccessibilityEvent

interface AccessibilityEvent : UIEvent {
  void initAccessibilityEvent(
         in DOMString typeArg,
         in boolean canBubbleArg,
         in boolean cancelableArg,
         in views::AbstractView viewArg,
         in long detailArg
       );
};

The different types of AccessibilityEvents that can occur are:

AXFocus (Editorial Note: possibly renamed AXFocusIn)

Initiated when the assistive technology cursor moves to a particular DOM node.

• Bubbles: Yes
• Cancelable: No
• Context Info: None

AXBlur (Editorial Note: possibly renamed AXFocusOut)

Initiated when the assistive technology cursor leaves a particular DOM node.

• Bubbles: Yes
• Cancelable: No
• Context Info: None

AXDragSelect

Initiated by the assistive technology in order to inform the web application than a draggable element (e.g. an element with an explicit aria-grabbed value) should be marked for dragging.

• Bubbles: Yes
• Cancelable: Yes
• Context Info: None

AXDragCancel

Editorial Note: This event may not be necessary; could use general EscapeRequest instead.

Initiated by the assistive technology in order to inform the web application than the current drag operation should be cancelled.

• Bubbles: Yes
• Cancelable: No … Editorial Note: Does this need to be cancelable?
• Context Info: None

AXDragDrop

Initiated by the assistive technology in order to inform the web application than a specific drop target (e.g. an element with an explicit aria-dropeffect value) should receive the drop event of the current drag operation.

• Bubbles: Yes
• Cancelable: Yes
• Context Info: None