nsIAccessible

Summary

The nsIAccessible interface is a cross-platform interface that supports platform-specific accessibility APIs like MSAA and ATK. Contains the sum of what's needed to support IAccessible as well as ATK's generic accessibility objects.

Can also be used by in-process accessibility clients to get information about objects in the accessible tree. The accessible tree is a subset of nodes in the DOM tree -- such as documents, focusable elements and text. Mozilla creates the implementations of nsIAccessible on demand.

 [scriptable, uuid=(c7520419-87ec-42bc-98cc-04c0bf173530)]
 interface nsIAccessible : nsISupports { ... };

accessible/public/nsIAccessible.idlScriptable

Please add a summary to this article.

Last changed in Gecko 1.9.2 (Firefox 3.6 / Thunderbird 3.1 / Fennec 1.0)

Overview

This section provides short overview of methods and attributes of this interface. All methods and attributes are grouped by categories.

Role, states and name

These includes main properties used to describe the accessible.

nsIAccessible.role to get the role of the accessible
nsIAccessible.getState() to get states of the accessibe
nsIAccessible.name, nsIAccessible.value to get the name and the value of the accessible

Tree navigation

You can navigate through the accessible tree by the following methods and attributes.

nsIAccessible.parent to get the parent accessible
nsIAccessible.nextSibling, nsIAccessible.previousSibling to get sibling accessibles
nsIAccessible.firstChild, nsIAccessible.lastChild to get first and last child
nsIAccessible.children, nsIAccessible.getChildAt(), nsIAccessible.childCount to navigate through the children by index

Accessible position

You can use nsIAccessible.indexInParent to get accessible index in its parent. Use nsIAccessible.groupPosition() to get information about this accessible in its group.

Relations

Many accessibles are linked with each other, for example, if one accessible gives the accessible name for another accessible (for example, html:label and html control) then these accessibles are related, please refer to relations documentation for more information. You can get related accessibles by methods

Focus and selection

In order to focus an accessible or get focused child accessible use nsIAccessible.takeFocus() and nsIAccessible.focusedChild.

To select an accessible you can use nsIAccessible.setSelected(), nsIAccessible.takeSelection() and nsIAccessible.extendSelection().

Actions

You can prepare actions on some accessibles (for example on button accessible). The following methods are intended for this nsIAccessible.actionCount, nsIAccessible.getActionName(), nsIAccessible.getActionDescription() and nsIAccessible.doAction().

Descriptions

nsIAccessible.description and nsIAccessible.help provides additional text information about accessible.

Attributes

Many accessibles exposes attributes to provide more details that cannot be fit into existing API methods, please refer to attributes documentation for more information. You can use nsIAccessible.attributes to get a map of attributes.

Keyboard shortcuts

Some actions on accessibles can be performed by keyboard shortcuts. Following methods are used to get them nsIAccessible.defaultKeyBinding(), nsIAccessible.getKeyBindings(), nsIAccessible.keyboardShortcut.

Size and screen position

You can use nsIAccessible.getBounds() to get size and coordinates of the accessible.

Layout oriented methods

nsIAccessible.getChildAtPoint() to get child accessible from point
nsIAccessible.getAccessibleToLeft(), nsIAccessible.getAccessibleToRight(), nsIAccessible.getAccessibleAbove() or nsIAccessible.getAccessibleBelow() to get left, right, top or below placed accessible

Methods

getKeyBindings: Provides array of localized string of global keyboard accelerator for the given action index supported by accessible.

getState: Provides a bit fields of accessible states which describe boolean properties of accessible.

groupPosition: This method returns grouping information. Used for tree items, list items, tab panel labels, radio buttons, etc. Also used for collectons of non-text objects.

getChildAtPoint: This method returns an accessible child which contains the coordinate at (x, y) in screen pixels.

getChildAt: This method returns Nth accessible child using zero-based index or last child if index than less than zero.

getAccessibleToRight: This method returns an accessible node geometrically to the right of this one.

getAccessibleToLeft: This method returns an accessible node geometrically to the left of this one.

getAccessibleAbove: This method returns an accessible node geometrically above this one.

getAccessibleBelow: This method returns an accessible node geometrically below this one.

getAccessibleRelated: This method returns an accessible related to this one by the given relation type.

getRelation: This method returns one accessible relation for this object.

getRelations: This method returns multiple accessible relations for this object.

getBounds: This method returns accessible's (x and y) coordinates relative to the screen and accessible's width and height.

setSelected: This method adds or remove this accessible to the current selection.

extendSelection: This method extends the current selection from its current accessible anchor node to this accessible.

takeSelection: This method selects this accessible node only.

takeFocus: This method focuses this accessible node.
getActionName: This method retrieves the name of the accessible action at the given zero-based index.

getActionDescription: This method retrieves the description of the accessible action at the given zero-based index.

doAction: This method performs the accessible action at the given zero-based index. Action number 0 is the default action.

Attributes

parent: Parent node in accessible tree.

nextSibling: Next sibling in accessible tree.

previousSibling: Previous sibling in accessible tree.

firstChild: First child in accessible tree.

lastChild: Last child in accessible tree.

children: Array of all this element's children.

childCount: Number of accessible children.

indexInParent: The 0-based index of this accessible in its parent's list of children, or -1 if this accessible does not have a parent.

name: Accessible name -- the main text equivalent for this node.

value: Accessible value -- a number or a secondary text equivalent for this node. Widgets that use role attribute can force a value using the valuenow attribute.

description: Accessible description -- long text associated with this node.

keyboardShortcut: Provides localized string of accesskey name, such as Alt+D. The modifier may be affected by user and platform preferences. Usually alt+letter, or just the letter alone for menu items.

defaultKeyBinding: Provides localized string of global keyboard accelerator for default action, such as Ctrl+O for Open file.

role: Enumerated accessible role for the associated element.

help: Help text associated with node.

focusedChild: Focused accessible child of node.

attributes: Attributes of accessible.

relationsCount: Returns the number of accessible relations for this object.

numActions: The number of accessible actions associated with this accessible.