1.1 Rich Internet Application Accessibility
§
The domain of web accessibility defines how to make web content usable by persons with disabilities. Persons with certain types of disabilities use
assistive technologies (
AT) to interact with content. Assistive technologies can transform the presentation of content into a format more suitable to the user, and can allow the user to interact in different ways. For example, the user may need to, or choose to, interact with a slider widget via arrow keys, instead of dragging and dropping with a mouse. In order to accomplish this effectively, the software needs to understand the
semantics of the content. Semantics is the science of meaning; in this case, used to assign roles, states, and properties that apply to user interface and content elements as a human would understand. For instance, if a paragraph is semantically identified as such, assistive technologies can interact with it as a unit separable from the rest of the content, knowing the exact boundaries of that paragraph. An adjustable range slider or collapsible list (a.k.a. a tree
widget) are more complex examples, in which various parts of the widget have semantics that need to be properly identified for assistive technologies to support effective interaction.
New technologies often overlook semantics required for accessibility, and new authoring practices often misuse the intended semantics of those technologies.
Elements that have one defined meaning in the language are used with a different meaning intended to be understood by the user.
For example, web application developers create collapsible tree widgets in
HTML using
CSS and JavaScript even though
HTML has no semantic
tree element. To a non-disabled user, it may look and act like a collapsible tree widget, but without appropriate semantics, the tree widget may not be
perceivable to, or
operable by, a person with a disability because assistive technologies may not recognize the role. Similarly, web application developers create interactive button widgets in
SVG using JavaScript even though
SVG has no semantic
button element. To a non-disabled user, it may look and act like a button widget, but without appropriate semantics, the button widget may not be
perceivable to, or
operable by, a person with a disability because assistive technologies may not recognize the role.
The incorporation of
WAI-ARIA is a way for an author to provide proper semantics for custom widgets to make these widgets accessible, usable, and interoperable with assistive technologies. This specification identifies the types of widgets and structures that are commonly recognized by accessibility products, by providing an
ontology of corresponding
roles that can be attached to content. This allows elements with a given role to be understood as a particular widget or structural type regardless of any semantics inherited from the implementing host language. Roles are a common property of platform
accessibility APIs which assistive technologies use to provide the user with effective presentation and interaction.
Roles are element types and will not change with time or user actions. Role information is used by assistive technologies, through interaction with the user agent, to provide normal processing of the specified element type.
States and properties are used to declare important attributes of an element that affect and describe interaction. They enable the
user agent and operating system to properly handle the element even when the attributes are dynamically changed by client-side scripts. For example, alternative input and output technology, such as screen readers and speech dictation software, need to be able to recognize and effectively manipulate and communicate various interaction states (e.g., disabled, checked) to the user.
Figure 1.0 illustrates the relationship between user agents (e.g., browsers), accessibility
APIs, and assistive technologies. It describes the "contract" provided by the user agent to assistive technologies, which includes typical accessibility information found in the accessibility
API for many of our accessible platforms for GUIs (role, state, selection,
event notification,
relationship information, and descriptions). The
DOM, usually
HTML, acts as the data model and view in a typical model-view-controller relationship, and JavaScript acts as the controller by manipulating the style and content of the displayed data. The user agent conveys relevant information to the operating system's accessibility
API, which can be used by any assistive technologies, such as screen readers.
Figure 1: The contract model with accessibility
APIs
Users of alternate input devices need
keyboard accessible content. The new semantics, when combined with the recommended keyboard interactions provided in
WAI-ARIA Authoring Practices, will allow alternate input solutions to facilitate command and control via an alternate input solution.
WAI-ARIA introduces navigational
landmarks through its Roles Model and the
XHTML role landmarks, which can help persons with dexterity and vision impairments by providing for improved keyboard navigation.
WAI-ARIA may also be used to assist persons with cognitive learning disabilities. The additional semantics allow authors to restructure and substitute alternative content as needed.
Assistive technologies need the ability to support alternative inputs by getting and setting the current value of
widget states and properties. Assistive technologies also need to determine what
objects are selected and manage widgets that allow multiple selections, such as list boxes and grids.
Speech-based command and control systems can benefit from
WAI-ARIA semantics like the
role attribute to assist in conveying audio information to the user. For example, upon encountering an element with a role of
menu with child elements of role
menuitem each containing text content representing a different flavor, a speech system might state to the user, "Select one of three choices: chocolate, strawberry, or vanilla."
WAI-ARIA is intended to be used as a supplement for native language semantics, not a replacement. When the host language provides a feature that provides equivalent accessibility to the
WAI-ARIA feature, use the host language feature.
WAI-ARIA should only be used in cases where the host language lacks the needed
role,
state, and
property indicators. Use a host language feature that is as similar as possible to the
WAI-ARIA feature, then refine the meaning by adding
WAI-ARIA. For instance, a multi-selectable grid could be implemented as a table, and then
WAI-ARIA used to clarify that it is an interactive grid, not just a static data table. This allows for the best possible fallback for user agents that do not support
WAI-ARIA and preserves the integrity of the host language semantics.
WAI-ARIA relies on user agent support for its features in two ways:
- Mainstream user agents use WAI-ARIA to alter how host language features are exposed to accessibility APIs in order to improve accessibility. The mechanism for this is defined in the Core Accessibility API Mappings.
- Assistive technologies use the enhanced information available in an accessibility API, or uses the WAI-ARIA markup directly via the DOM, to convey semantic and interaction information to the user.
Aside from using
WAI-ARIA markup to improve what is exposed to accessibility
APIs, user agents behave as they would natively. Assistive technologies react to the extra information in the accessibility
API as they already do for the same information on non-web content. User agents that are not assistive technologies, however, need do nothing beyond providing appropriate updates to the accessibility
API.
The
WAI-ARIA specification neither requires nor forbids user agents from enhancing native presentation and interaction behaviors on the basis of
WAI-ARIA markup. Mainstream user agents might expose
WAI-ARIA navigational landmarks (for example, as a dialog box or through a keyboard command) with the intention to facilitate navigation for all users. User agents are encouraged to maximize their usefulness to users, including users without disabilities.
WAI-ARIA is intended to provide missing semantics so that the intent of the author may be conveyed to assistive technologies. Generally, authors using
WAI-ARIA will provide the appropriate presentation and interaction features. Over time, host languages may add
WAI-ARIA equivalents, such as new form controls, that are implemented as standard accessible user interface controls by the user agent. This allows authors to use them instead of custom
WAI-ARIA enabled user interface components. In this case the user agent would support the native host language feature. Developers of host languages that implement
WAI-ARIA are advised to continue supporting
WAI-ARIA semantics when they do not adversely conflict with implicit host language semantics, as
WAI-ARIA semantics more clearly reflect the intent of the author if the host language features are inadequate to meet the author's needs.
1.4 Co-Evolution of WAI-ARIA and Host Languages
§
WAI-ARIA is intended to augment semantics in supporting languages like [
HTML] and [
SVG2], or to be used as an accessibility enhancement technology in other markup-based languages that do not explicitly include support for ARIA. It clarifies semantics to assistive technologies when authors create new types of objects, via style and script, that are not yet directly supported by the language of the page, because the invention of new types of objects is faster than standardized support for them appears in web languages.
It is not appropriate to create objects with style and script when the host language provides a semantic element for that type of object. While
WAI-ARIA can improve the accessibility of these objects, accessibility is best provided by allowing the user agent to handle the object natively. For example, it's better to use an
h1 element in
HTML than to use the
heading role on a
div element.
It is expected that, over time, host languages will evolve to provide semantics for objects that currently can only be declared with
WAI-ARIA. This is natural and desirable, as one goal of
WAI-ARIA is to help stimulate the emergence of more semantic and accessible markup. When native semantics for a given feature become available, it is appropriate for authors to use the native feature and stop using
WAI-ARIA for that feature. Legacy content may continue to use
WAI-ARIA, however, so the need for user agents to support
WAI-ARIA remains.
While specific features of
WAI-ARIA may lose importance over time, the general possibility of
WAI-ARIA to add semantics to web pages is expected to be a persistent need. Host languages may not implement all the semantics
WAI-ARIA provides, and various host languages may implement different subsets of the features. New types of objects are continually being developed, and one goal of
WAI-ARIA is to provide a way to make such objects accessible, because web authoring practices often advance faster than host language standards. In this way,
WAI-ARIA and host languages both evolve together but at different rates.
Some host languages exist to create semantics for features other than the user interface. For example,
SVG expresses the semantics behind production of graphical objects, not of user interface components that those objects may represent. Host languages might, by design, not provide native semantics that map to
WAI-ARIA features. In these cases,
WAI-ARIA could be adopted as a long-term approach to add semantic information to user interface components.
1.6 Assistive Technologies
§
Programmatic access to accessibility semantics is essential for assistive technologies. Most assistive technologies interact with user agents, like other applications, through a recognized accessibility
API. Perceivable objects in the user interface are exposed to assistive technologies as accessible objects, defined by the accessibility
API interfaces. To do this properly, accessibility information – role, states, properties as well as contextual information – needs to be accurately conveyed to the assistive technologies through the accessibility
API. When a state change occurs, the user agent provides the appropriate event notification to the accessibility
API. Contextual information, in many host languages like
HTML, can be determined from the
DOM itself as it provides a contextual tree hierarchy.
While some assistive technologies interact with these accessibility
APIs, others may access the content directly from the
DOM. These technologies can restructure, simplify, style, or reflow the content to help a different set of users. Common use cases for these types of adaptations may be the aging population, persons with cognitive impairments, or persons in environments that interfere with use of their tools. For example, the availability of regional navigational landmarks may allow for a mobile device adaptation that shows only portions of the content at any one time based on its semantics. This could reduce the amount of information the user needs to process at any one time. In other situations it may be appropriate to replace a custom user interface control with something that is easier to navigate with a keyboard, or touch screen device.