ISO/IEC TR 13066-4:2015

TECHNICAL ISO/IEC TR
REPORT 13066-4
First edition
2015-11-01
Information technology —
Interoperability with assistive
technology (AT) —
Part 4:
Linux/UNIX graphical environments
accessibility API
Technologies de l’information — Interopérabilité avec les
technologies d’assistance —
Partie 4: Accessibilité API des environnements graphiques lInux/UNIX
Reference number
ISO/IEC TR 13066-4:2015(E)
©
ISO/IEC 2015

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ISO/IEC TR 13066-4:2015(E)

COPYRIGHT PROTECTED DOCUMENT
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ISO/IEC TR 13066-4:2015(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Terms and definitions . 1
3 Overview . 4
3.1 General description . 4
3.2 Architecture . 5
3.2.1 ATK Aware Toolkits . 6
3.2.2 AT-SPI Aware Assistive Technologies .11
3.3 Support apart from AT-SPI/ATK .12
4 Using the API .12
4.1 Overview .12
4.2 User Interface elements .12
4.3 Getting and setting focus .13
4.4 Communication mechanisms .14
4.5 How GNOME uses the ATK/AT-SPI accessibility Application Programming Interface .14
5 Exposing User Interface Element Information .15
5.1 Role, state(s), boundary, name, and description of the user interface element.15
5.2 Current value and any minimum or maximum values, if the user interface element
represents one of a range of values .16
5.3 Text contents, text attributes, and the boundary of text rendered to the screen .17
5.4 The location of the user interface element in relation to other user interface elements .17
6 Exposing User Interface Element Actions .18
7 Keyboard focus .18
8 Events .19
8.1 Changes in the user interface element value .19
8.2 Changes in the name of the user interface element .20
8.3 Changes in the description of the user interface element .20
8.4 Changes in the boundary of the user interface element .20
9 Programmatic modifications of states, properties, values, and text .20
10 Design considerations .21
10.1 Using AT-SPI/ATK .21
11 Further information .21
11.1 Testing Accessibility with Accerciser .22
Bibliography .23
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ISO/IEC TR 13066-4:2015(E)

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical
activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international
organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the
work. In the field of information technology, ISO and IEC have established a joint technical committee,
ISO/IEC JTC 1.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for
the different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/IEC JTC 1, Information technology, Subcommittee
SC 35, User interfaces.
ISO/IEC 13066 consists of the following parts, under the general title Information technology —
Interoperability with Assistive Technology (AT):
— Part 1: Requirements and recommendations for interoperability
— Part 2: Windows accessibility application programming interface (API) [Technical Report]
— Part 3: IAccessible2 accessibility application programming interface (API) [Technical Report]
— Part 4: Linux/UNIX graphical environments accessibility API [Technical Report]
— Part 6: Java accessibility application programming interface (API) [Technical Report]
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Introduction
Assistive technology (AT) is specialized information technology (IT) hardware or software that is
added to or incorporated within a system that increases accessibility for an individual. In other words,
it is special purpose IT that interoperates with another IT product enabling a person with a disability to
use the IT product.
Interoperability involves the ability to add or replace Assistive Technology (AT) to existing components
of Information Technology (IT) systems. Interoperability between AT and IT is best facilitated via the
use of standardized, public interfaces for all IT components.
This part of ISO/IEC 13066 describes the following.
AT-SPI
The Assistive Technology Service Provider Interface (AT-SPI) API, which can be used as a toolkit
agnostic framework to support software to software IT-AT interoperability on Linux and UNIX
graphical desktop environments.
ATK
The Accessibility Toolkit (ATK) library provides a set of interfaces in support of AT-SPI on the GUI
application side. The interfaces are toolkit-independent implementations could be written for any
widget set, such as GTK, Motif, or Qt.
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TECHNICAL REPORT ISO/IEC TR 13066-4:2015(E)
Information technology — Interoperability with assistive
technology (AT) —
Part 4:
Linux/UNIX graphical environments accessibility API
1 Scope
This part of ISO/IEC 13066 provides an overview to the structure and terminology of the Linux/UNIX
graphical environments accessibility API.
It will provide the following:
— a description of the overall architecture and terminology of the API;
— further introductory explanations regarding the content and use of the API beyond those found in
ISO/IEC 13066-1:2011, Annex A;
— an overview of the main properties, including
— of user interface elements,
— of how to get and set focus, and
— of communication mechanisms in the API;
— a discussion of design considerations for the API (e.g. pointers to external sources of information on
accessibility guidance related to using the API);
— information on extending the API (and where this is appropriate);
— an introduction to the programming interface of the API (including pointers to external sources of
information).
It will provide this information as an introduction to the Java API to assist the following:
— IT system level developers who create custom controls and/or interface to them;
— AT developers involved in programming “hardware to software” and “software to software”
interactions.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
A11Y
short form of “accessibility” or of “accessible”
2.2
accessible object
part of the user interface (2.21) that is accessible by and exposes the Java accessibility API
Note 1 to entry: An accessible object is represented by an object of the “AccessibleContext” Java class.
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2.3
application programming interface
API
collection of invocation methods and associated parameters used by one piece of software to request
actions from another piece of software
2.4
application software
software that is specific to the solution of an application problem
EXAMPLE A spreadsheet program is application software.
2.5
assistive technology
AT
hardware or software that is added to or incorporated within a system that increases accessibility for
an individual
EXAMPLE Braille displays, screen readers, screen magnification software, and eye tracking devices are
assistive technologies.
[SOURCE: ISO 9241-171:2008, 3.5]
Note 1 to entry: Within this part of ISO/IEC 13066, where Assistive Technology (AT) is used, it is to be considered
as both singular and plural, without distinction. If it is to be used in the singular only, it will be preceded by the
article “an” (i.e. an Assistive Technology). If it is to be used in the plural only, it will be preceded by the adjective
“multiple” (i.e. multiple AT).
2.6
ATK
The Accessibility Toolkit
library which describes a set of interfaces that support the AT-SPI on the GUI application side
Note 1 to entry: The ATK interfaces are toolkit-independent - implementations could be written for any widget
set, such as GTK, Motif or Qt.
2.7
AtkObject
base object class for the Accessibility Toolkit API
Note 1 to entry: This is the ATK analog of MSAA’s and IAccessible2’s “accessible object”. The AtkObject structure
is not accessed directly.
2.8
AT-SPI
The Assistive Technology Service Provider Interface
API that can be used as a toolkit agnostic framework to support software to software IT-AT
interoperability on Linux and UNIX graphical desktop environments
2.9
clients
components that use the services of another component
Note 1 to entry: In this part of ISO/IEC 13066, client refers more specifically to a component that uses the services
of either or both AT-SPI and/or ATK to access, identify, or manipulate the UI elements of an application.
2.10
daemon
software application that is not invoked explicitly, but lies dormant waiting for some condition(s) to occur
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2.11
embedded device
embedded system
computer system designed to perform one or a few dedicated functions often with real-time
computing constraints
Note 1 to entry: It is embedded as part of a complete device often including hardware and mechanical parts. By
contrast, a general-purpose computer, such as a personal computer (PC), is designed to be flexible and to meet a
wide range of end-user needs. Embedded systems control many devices in common use today.
Note 2 to entry: In general, “embedded system” is not a strictly definable term, as most systems have some element
of extensibility or programmability, e.g. hand-held computers share some elements with embedded systems
such as the operating systems and microprocessors which power them, but they allow different applications
to be loaded and peripherals to be connected. Moreover, even systems which don’t expose programmability
as a primary feature generally need to support software updates. On a continuum from “general purpose” to
“embedded,” large application systems will have subcomponents at most points even if the system as a whole is
“designed to perform one or a few dedicated functions,” and is thus appropriate to call “embedded.”
2.12
function
defined objective or characteristic action of a system or component, e.g. a system has inventory control
as its primary function
[SOURCE: IEEE Std. 610.12-1990]
2.13
interface
shared boundary between two functional units, defined by various characteristics pertaining to the
functions, physical interconnections, signal exchanges, and other characteristics, as appropriate
2.14
interoperability
capability to communicate, execute programs, or transfer data among various functional units in a
manner that requires the user to have little or no knowledge of the unique characteristics of those units
2.15
inter-process communication
IPC
mechanism by which different software processes communicate with each other – across process
boundaries, runtime environments, and sometimes also computers and operating systems (2.16)
2.16
operating system
OS
software that controls the execution of programs and that may provide services such as resource
allocation, scheduling, input-output control, and data management
Note 1 to entry: Although operating systems are predominantly software, partial hardware implementations
are possible.
2.17
servers
in the context of this part of ISO/IEC 13066 and of assistive technology, servers are components
(applications, libraries, etc.) that have UI and expose information about the UI and/or allow it to be
manipulated
2.18
service
functionality made available to a user electronically, e.g. airline reservation service, currency
translation services, weather forecasting, restaurant recommendations are all services
[SOURCE: ISO/IEC 24752-1:2014, 4.27]
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2.19
software
all or part of the programs, procedures, rules, and associated documentation of an information
processing system
Note 1 to entry: Software is an intellectual creation that is independent of the medium on which it is recorded.
2.20
system software
platform software
application-independent software that supports the running of application software (2.4), e.g. an
operating system (2.16), a Web browser, or a programming environment – Java can be used as a platform
for application software
2.21
user interface
UI
mechanisms by which a person interacts with a computer system
Note 1 to entry: The user interface provides input mechanisms, allowing users to manipulate a system. It also
provides output mechanisms, allowing the system to produce the effects of the users’ manipulation.
2.22
user interface element
user interface object
user interface component
entity of the user interface that is presented to the user by the software
[SOURCE: ISO 9241-171:2008, 3.38]
Note 1 to entry: User interface elements may or may not be interactive.
Note 2 to entry: Both entities relevant to the task and entities of the user interface are regarded as user interface
elements. Different user interface element types are text, graphics, and controls. A user interface element may be
a representation or an interaction mechanism for a task object (such as a letter, a sales order, electronic parts, or
a wiring diagram) or a system object (such as a printer, hard disk, or network connection). It may be possible for
the user to directly manipulate some of these user interface elements.
EXAMPLE 1 User interface elements in a graphical user interface include such things as basic objects (such
as window title bars, menu items, push buttons, image maps, and editable text fields) or containers (such as
windows, grouping boxes, menu bars, menus, groups of mutually-exclusive option buttons, and compound images
that are made up of several smaller images).
EXAMPLE 2 User interface elements in an audio user interface include such things as menus, menu items,
messages, and action prompts.
EXAMPLE 3 User interface elements in tactile interfaces include such things as tactile dots, tactile bars,
surfaces, knobs, and grips.
3 Overview
3.1 General description
AT-SPI/ATK was originally developed by Sun Microsystems for the GNOME platform, a common and
accessible graphical desktop for Linux / UNIX graphical environments. GNOME is an open source project
delivering a collection of software libraries and applications. It was formerly rationalized as an acronym
meaning GNU Network Object Model Environment. From the beginning, AT-SPI/ATK has served as a
platform-neutral, toolkit agnostic framework for providing bi-directional communication between
AT and applications. Through the use of AT-SPI, an application’s components’ state, property, and role
information is communicated directly to the end user’s AT, thereby facilitating bi-directional (input
and output) user interactivity with, and control over, an application or compound document instance.
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It includes support for rich text, tables, and relationships between objects, self-describing actions,
application-specific information, and extensible object properties to support Web 2.0 applications.
As of this writing, both the GNOME and KDE platforms directly support AT-SPI/ATK on Linux/UNIX
graphical desktops. For applications, support is available through several specific user interface
toolkits, including GTK+ (a library for creating graphical user interfaces which works on many UNIX-
like platforms, Windows, and on framebuffer devices), UNO, XUL, and Java/Swing (as described in
ISO/IEC TR 13066-6). It can also be achieved by implementing support for ATK or the Java Accessibility
API directly, or by AT-SPI directly.
3.2 Architecture
Accessibility support on Linux/UNIX graphical desktops implements the familiar client-server
paradigm. The GNOME Accessibility Architecture provided on most Linux and UNIX graphical desktops
-the only accessibility architecture available for Linux and UNIX graphical desktops as of this writing-
distinguishes among ATK aware applications, assistive technologies and an accessibility broker.
Communications between applications and assistive technologies (AT) is achieved using AT-SPI, which
facilitates communications with ATK aware applications on the one hand, and with AT on the other.
Generally, only AT is directly aware of AT-SPI.
Key
(g)
GNOME
Figure 1 — AT-SPI/ATK Architecture Overview
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Key
(g)
GNOME
(j)
Java; everything else is Application
Figure 2 — Application Toolkits Supporting AT-SPI/ATK
3.2.1 ATK Aware Toolkits
ATK aware applications are applications that offer information about their user interface via the AT-SPI
protocol. This can be achieved in several ways.
— GNOME applications get AT-SPI support through the GTK+ toolkit they are based on. GTK+ optionally
loads theGNOMEAccessibility Implementation Library (GAIL), an implementation of the accessibility
interfaces defined by ATK, which bridges between the GNOME widgets and ATK. GAIL is provided
by GTK in libgail-util. A second library is used in order to bridge between ATK and AT-SPI.
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Key
(g)
GNOME
Figure 3 — GNOME Mag and the GNOMEShell
— Mozilla-based applications like Firefox and Thunderbird do not use GTK+ but implement the ATK
API directly within its applications using XUL Accessibility. The Mozilla Accessibility Architecture
is described at https://developer.mozilla.org/en-US/docs/Web/Accessibility/Architecture
and the XUL Accessibility Guidelines are published at https://developer.mozilla.org/en/XUL_
accessibility_guidelines.
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Key
(g)
GNOME
Figure 4 — Mozilla Applications
— The Apache OpenOffice and LibreOffice applications bridge to ATK using the UNO Accessibility API,
http://www.openoffice.org/ui/accessibility/unoapi.html.
Key
(g)
GNOME
Figure 5 — OpenOffice and derivatives
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— Java applications may either use the Java accessibility framework which directly bridges to AT-
SPI, or the new Java ATKwrapper https://git.gnome.org/browse/java-atk-wrapper/ Some Java
applications, built using the Eclipse libraries, simply use GTK+ directly, as show in in Figure 6.
Key
(g)
GNOME
(j)
Java; everything else is Application
Figure 6 — Java and Eclipse Applications
— WebKit support is being provided directly through WebKitGTK+, http://webkitGTK.org.
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Key
(g)
GNOME
(w)
WebKit; everything else is Application
Figure 7 — Applications based on WebKit
— KDE support utilizes a Qt plugin that bridges the QAccessible APIs to AT-SPI. The current approach
is unique in that it does not bridge via ATK, but rather bridges directly to AT-SPI through QT-AT-SPI,
http://gitorious.org/qt-at-spi.
Figure 8 — Applications based on KDE/Qt
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In the context of AT-SPI/ATK, applications are often called servers.
In order for an application to be accessible on the Linux/UNIX graphical desktop, it generally needs
to provide information about its user interface using ATK. The sole exception to date is KDE where Qt
applications are planned to bridge directly to AT-SPI.
If an application is written using GNOME’s GTK+, all of the standard widgets provide the needed
information to ATK and therefore the application will by default be accessible. Applications that do not
use GTK+ (or UNO, XUL, Java, Qt, or Webkit) for their user interface, as well as any custom widgets,
require additional work to make them accessible.
3.2.2 AT-SPI Aware Assistive Technologies
Assistive technologies are applications that are needed to obtain information about the user interfaces
of applications. Screen readers are assistive technologies commonly utilized by computer users who are
blind or severely visually impaired. A screen reader (like Orca, see https://live.gnome.org/Orca) needs
to know what to present to the user through synthetic text-to-speech (TTS), or through a refreshable
braille display. On-screen keyboards are assistive technologies commonly utilized by computer users
who cannot use the standard keyboard (QUERTY or other layout) or a mouse. An on-screen keyboard
(like Caribou, see https://live.gnome.org/Caribou) needs to send keyboard and mouse events to
the application. In the context of AT-SPI, assistive technologies are often called clients because they
consume and interact with application UI information.
The accessibility broker, ATK-Bridge (libatk-bridge), is a daemon that coordinates communication
between ATK aware applications and assistive technologies. Also referred to as the accessibility
bridge, this daemon necessarily links both to ATK and AT-SPI. Bridges are needed because different
toolkits commonly implement similar features differently. Bridges to AT-SPI ensure that AT receives
consistently formulated data. Each ATK aware application registers with the broker in order to offer
its information. Assistive technologies may add event listeners to the broker, so that they get informed
when accessibility related information in any application changes. They may also make queries of
applications directly.
Key
(g)
GNOME; everything else is Assistive technology
Figure 9 — ATK to AT layer
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3.3 Support apart from AT-SPI/ATK
Persons unable to use a keyboard and mouse sometimes use alternative input technology supported
through AT-SPI/ATK. However, many users can be accommodated programmatically through software
that causes a standard keyboard to behave differently. Many of these features and behaviours have long
been available in the XKeyboard Extension: Library Specification Library (X Version 11, Release 6.4)
http://accessibility.linuxfoundation.org/a11yspecs/kbd/kafs.html#xkb-ref.
Individuals with mobility impairments benefit by having such features built-in and available through
standard activation strategies, such as tapping the Shift key five times to activate StickyKeys. The
routines provided by this API also benefit assistive technologies such as on screen keyboard and screen
reader applications which do rely on AT-SPI/ATK.
The “Keyboard Access Functional Specification (KAFS),” http://accessibility.linuxfoundation.
org/allyspecs/kbd/kafs.html, developed by the Open A11y Workgroup, identifies and adopts a subset
of the XKBKeyboard Extens
...