This document describes how user agents determine names and descriptions of accessible objects from web content languages and expose them in accessibility APIs. This allows assistive technologies to associate and relay the name or description of objects to users. Documenting the algorithm and mappings promotes interoperable exposure of these properties and events as implemented by different accessibility APIs, and helps to ensure that this information appears in a manner consistent with author intent.
The accessible name and description computation and mappings specification defines support that applies across multiple content technologies. This includes accessible name and description provided by general-purpose WAI-ARIA [[!WAI-ARIA]] roles, states, and properties as well as features specific to individual content languages. The accessible name and description computation extends the mapping guidance provided by CORE-AAM [[!CORE-AAM]] and technology-specific accessibility API mappings.
This document updates and will eventually supersede the accessible name and description guidance in the WAI-ARIA 1.0 User Agent Implementation Guide [[!WAI-ARIA-IMPLEMENTATION]] W3C Recommendation. It is part of the WAI-ARIA suite described in the WAI-ARIA Overview.
This section is informative.
User agents acquire information from the DOM and create a parallel structure called the accessibility tree, made up of accessible objects. An accessible object provides information about its role, states, and properties. An example is an accessible object whose role is menuitem
, is currently in an enabled
state, with a haspopup
property, indicating that it leads to a sub-menu.
The two properties of accessible objects described in this document are its accessible name and accessible description. The name is a short label that provides information about the purpose of the object. An example of an accessible name for a menu item is New
, signifying that the menu item provides for the creation of new documents, windows, and so on.
The description is a short explanation that further clarifies the nature of the accessible object. It is not always necessary to provide a description if the name is sufficient, but it can help a user better understand the use of the object.
Accessibility APIs currently support flat, unstructured strings for accessible names and descriptions. The result of the name/description computation is thus a flat string.
The terms "accessible name" and "accessible description" are used to emphasize that they are properties of accessible objects as exposed by Accessibility APIs. However, they are frequently referred to hereafter as simply "name" and "description".
This section is normative.
This specification indicates whether a section is normative or informative and the classification applies to the entire section. A statement "This section is normative" or "This section is informative" applies to all sub-sections of that section.
Normative sections provide requirements that user agents must follow for an implementation to conform to this specification. The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted as described in Keywords for use in RFCs to indicate requirement levels [[!RFC2119]]. RFC-2119 keywords are formatted in uppercase and contained in a strong
element with class="rfc2119"
. When the keywords shown above are used, but do not share this format, they do not convey formal information in the RFC 2119 sense, and are merely explanatory, i.e., informative. As much as possible, such usages are avoided in this specification.
Informative sections provide information useful to understanding the specification. Such sections may contain examples of recommended practice, but it is not required to follow such recommendations in order to conform to this specification.
This section is normative.
This section is normative.
The starting point of the name and description computation is a DOM element. The output is a flat, unstructured string that can be as simple as a single word, or a string of space-separated tokens. Examples include Save
and Reload from disk
.
An important factor is the element's role, that determines which content contributes to the name string. Roles have a nameFrom
RDF property, with two possible values:
aria-label
and aria-labelledby
attribute, or a host language labeling mechanism, such as the alt
or title
attribute in HTML, or the desc
element in SVG. (Joseph) Need links into ARIA spec to (1) a list of nameFrom:author roles, and (2) a list of nameFrom:contents roles. Reference these at step 2F below.
User agents MUST compute an accessible name using the rules outlined below in the section titled Text Alternative Computation.
If aria-describedby
is present, user agents MUST compute the accessible description by concatenating the text alternatives for elements referenced by an aria-describedby
attribute on the current element. The text alternatives for the referenced elements are computed using a number of methods, outlined below in the section titled Text Alternative Computation.
The text alternative computation is used to generate both the accessible name and accessible description. There are different rules provided for several different types of elements, nodes, and combinations of markup. Text alternatives are built up, when appropriate, from all the relevant content contained within an element. This is accomplished via steps 2B and 2F, which are recursive, using the full set of rules to retrieve text from its own children or nodes it references.
The purpose of the computation is to create a perceivable label or description for alternative presentations, in the form of a flat string of space separated textual tokens.
root node
's text equivalent. Initially, the current node
is the root node
, but at later stages is either some descendant of the root node
, or another referenced node.current node
.result
to X.result
to the end of X.result
to X.result
to X after the space.result
to X.result
to the start of X.result
to X.result
to the start of X, and add a space after the copy.The text alternative for a given element is computed as follows:
root node
to the given element, the current node
to the root node
, and the total accumulated text
to the empty string ("").current node
:
current node
is hidden and is not referenced by aria-labelledby
or aria-describedby
, nor referenced by a native host language text alternative element or attribute, return the empty string.
By default, assistive technologies do not relay hidden information, but an author can explicitly override that and include hidden text as part of the accessible name or accessible description by using aria-labelledby
or aria-describedby
.
current node
has a non-empty aria-labelledby
attribute, and the current node
is not already part of an aria-labelledby
traversal, process its IDREFs in the order they occur: current node
has a non-empty aria-describedby
attribute, and the current node
is not already part of an aria-describedby
traversal, process its IDREFs in the order they occur:
accumulated text
to the empty string.current node
to the node referenced by the IDREF.current node
beginning with step 2. Set the result
to that text alternative.result
, with a space, to the accumulated text
.accumulated text
.The following example shows the meaning of the clause "… and the current node
is not already part of an aria-labelledby
traversal …" .
element1
's accessible name is "hello" because this is a first traversal of its aria-labelledby
, leading to element3
.element2
has no accessible name. The computation involves a first traversal of its aria-labelledby
leading to element1
, but element1
's aria-labelledby
is not subsequently followed. <element1 id="el1" aria-labelledby="el3" />
<element2 id="el2" aria-labelledby="el1" />
<element3 id="el3"> hello </element3>
current node
has a non-empty aria-label
attribute:
current node
is due to recursion and the current node
is an embedded control as defined in step 2E, ignore aria-label
and skip to rule 2E.aria-label
.The following example shows the interaction of aria-labelledby
and aria-label
when a node has an aria-labelledby
that refers to itself. The <span role="button">
elements have the accessible names "Delete Documentation.pdf" and "Delete HolidayLetter.pdf", respectively.
<h1>Files</h1>
<ul>
<li>
<a id="file_row1" href="./files/Documentation.pdf">Documentation.pdf</a>
<span role="button" tabindex="0" id="del_row1" aria-label="Delete" aria-labelledby="del_row1 file_row1"></span>
</li>
<li>
<a id="file_row2" href="./files/HolidayLetter.pdf">HolidayLetter.pdf</a>
<span role="button" tabindex="0" id="del_row2" aria-label="Delete" aria-labelledby="del_row2 file_row2"></span>
</li>
</ul>
current node
's native markup provides an attribute or element that defines a text alternative, return that alternative as a flat string
, unless the element is marked as presentational (role="presentation"
or role="none"
).
Above wording taken from second note in ISSUE-522.
For example, in HTML, the img
element's alt
attribute defines a text alternative string, and the label
element provides text for the referenced form element. In SVG2, the desc
and title
elements provide a description of their parent element.
current node
is a control embedded within the label of another widget, where the user can adjust the embedded control's value, then include the embedded control as part of the text alternative in the following manner:
aria-valuetext
property is present, return its value, aria-valuenow
property is present, return its value,Consider a check box label that contains a text input field: "Flash the screen [input] times". If the user has entered "5" for the embedded textbox, the complete label is "Flash the screen 5 times", e.g.:
<div role="checkbox" aria-checked="false">Flash the screen <span role="textbox" aria-multiline="false"> 5 </span> times</div>
current node's
role allows "Name From: contents", or if the current node
is referenced by aria-labelledby
, aria-describedby
, or is a native host language text alternative element:
accumulated text
to the empty string.current node
and include it in the accumulated text
:
list-style-type
is not "none"
, user agents MUST prepend the list item indicator text to the item's text. If the list item indicator text includes a space, prepend the indicator text without a space; otherwise prepend with a space.:before
and :after
pseudo elements can provide textual content for elements that have a content model.
:before
pseudo elements, User agents MUST prepend CSS textual content, without a space, to the textual content of the current node
. :after
pseudo elements, User agents MUST append CSS textual content, without a space, to the textual content of the current node
. current node
:
current node
to the child node.current node
beginning with step 2. Set the result
to that text alternative.result
to the accumulated text
. (Joseph) the last step above needs work since there are cases where you "append with a space" and others where you "append without a space". Example of the latter: <label> <input type="checkbox"> Make this the <em>top</em>most element</label>
. The result is "Make this the topmost element", not "Make this the top most element" – do not append a space after "top".
accumulated text
.Important: Each node in the subtree is consulted only once. If text has been collected from a descendant, but is referenced by another IDREF in some descendant node, then that second, or subsequent, reference is not followed. This is done to avoid infinite loops.
This step can apply to the child nodes themselves, which means the computation is recursive and results in text collected from all the elements in the current node
's subtree, no matter how deep it is. However, any given descendant node's text alternative can result from higher precedent markup described in steps B through D above, where "Namefrom: author" attributes provide the text alternative for the entire subtree.
current node
is a Text node, return its textual contents.current node
has a tooltip attribute, return its value.
Tooltip attributes are used only if nothing else, including subtree content, has provided results.
(Joseph) Define "tooltip attribute"?
Append the result
of each step above, with a space, to the total accumulated text
.
After all steps are completed, the total accumulated text
is used as the accessible name or accessible description of the element that initiated the computation.
Each step of the algorithm generates a flat text string
. An implementation trims the text and concatenates it with the text alternative computed by previous steps. The result is a single flat string name or description associated with the element for which the text alternative computation was executed. The computed string is used to set the accessible name or accessible description property of the accessible object corresponding to the element. The specifics of each accessibility API mapping is given in the following table.
Accessibility API Property | MSAA + IAccessible2 | UIA | ATK/AT-SPI | AXAPI |
---|---|---|---|---|
accessible name |
Expose in accName property.
|
Expose in Name property.
|
Expose in the name property of the accessible object.
|
Expose as string AXTitle , AXDescription , or AXTitleUIElement :
|
accessible description |
Expose in accDescription property.
|
TBD.
(See ACTION-1104) |
Expose in the description property of the accessible object.
|
Expose as string AXHelp . |
More information concerning name and description accessibility API mappings, including relationships, such as labelled-by/label-for and described-by/description-for, is documented in the Core Accessibility API Mappings document [[!CORE-AAM]]. See the mapping table entries for aria-label
, aria-labelledby
, and aria-describedby
.
(Joseph) Certain Accessibility APIs emit events for name and/or description property changes. Document that here (see, for example, FF bugzilla 991969).
Although rare, sometimes an accessible name or accessible description may change. Examples include:
The following table lists the events or notifications provided by Accessibility APIs if the name or description changes. Assistive technologies can make use of these events to provide the current label as needed.
Accessibility API Property | MSAA + IAccessible2 | UIA | ATK/AT-SPI | AXAPI |
---|---|---|---|---|
accessible name |
EVENT_OBJECT_NAMECHANGE |
PropertyChangeEvent |
object:property-change:accessible-name |
TitleChangedNotification |
accessible description |
EVENT_OBJECT_DESCRIPTIONCHANGE |
PropertyChangeEvent |
object:property-change:accessible-description |
TBD. |
<img>
to HTML-AAM.