Proposed Element with aria-hidden has no content in sequential focus navigation

Description

This rule checks that elements with an aria-hidden attribute do not contain elements that are part of the sequential focus navigation and focusable.

Applicability

This rule applies to any element with an aria-hidden attribute value of true.

Expectation

None of the target elements has an inclusive descendant in the flat tree that are focusable and part of the sequential focus navigation.

Assumptions

Interacting with the page does not result in changing the aria-hidden attribute value of target elements. An example of such a situation would be when closing a modal dialog makes previously hidden elements that were not focusable or part of the sequential focus navigation become focusable and part of the sequential focus navigation.

Accessibility Support

Some user agents treat the value of aria-hidden attribute as case-sensitive.

Background

Using aria-hidden="false" on a descendant of an element with aria-hidden="true" does not expose that element. aria-hidden="true" hides itself and all its content from assistive technologies.

By adding aria-hidden="true" to an element, content authors ensure that assistive technologies will ignore the element. This can be used to hide parts of a web page that are pure decoration, such as icon fonts - that are not meant to be read by assistive technologies.

An element with an aria-hidden attribute set to true that is also part of the sequential focus navigation may cause confusion for users of assistive technologies because the element can be reached via sequential focus navigation, but it should be hidden and not included in the accessibility tree.

The 1 second time span introduced in the exception of the definition of focusable is an arbitrary limit which is not included in WCAG. Given that scripts can manage the focus state of elements, testing the focused state of an element consistently would be impractical without a time limit.

Related rules

• Element with presentational children has no focusable content

Bibliography

• CSS Scoping Module Level 1 (editor’s draft)
• Understanding Success Criterion 1.3.1: Info and Relationships
• Understanding Success Criterion 4.1.2: Name, Role, Value
• aria-hidden (state)
• Fourth rule of ARIA use
• Element with presentational children has no focusable content

Accessibility Requirements Mapping

• 4.1.2 Name, Role, Value (Level A)

  • Learn more about 4.1.2 Name, Role, Value
  • Required for conformance to WCAG 2.0 and later on level A and higher.
  • Outcome mapping:
    • Any failed outcomes: success criterion is not satisfied
    • All passed outcomes: success criterion needs further testing
    • An inapplicable outcome: success criterion needs further testing
• Fourth rule of ARIA use

  • Learn more about Fourth rule of ARIA use
  • Not required for conformance to any W3C accessibility recommendation.
  • Outcome mapping:
    • Any failed outcomes: WAI-ARIA rule is not satisfied
    • All passed outcomes: WAI-ARIA rule needs further testing
    • An inapplicable outcome: WAI-ARIA rule needs further testing

Input Aspects

The following aspects are required in using this rule.

• DOM Tree
• CSS Styling

Test Cases

Passed

Passed Example 1

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This p element is not part of the sequential focus navigation.

<p aria-hidden="true">Some text</p>

Passed Example 2

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This a element is not part of the sequential focus navigation because it is hidden through CSS.

<div aria-hidden="true">
	<a href="/" style="display:none">Link</a>
</div>

Passed Example 3

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This input element is not part of the sequential focus navigation because of the disabled attribute.

<input disabled aria-hidden="true" />

Passed Example 4

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This a element is part of the sequential focus navigation, but moves focus to the input element whenever it receives focus.

<div aria-hidden="true">
	<a href="/" style="position:absolute; top:-999em" onfocus="document.querySelector('input').focus()">First link</a>
</div>
<input />

Passed Example 5

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This button element is focusable, but not part of the sequential focus navigation because of the tabindex attribute.

<div aria-hidden="true">
	<button tabindex="-1">Some button</button>
</div>

Failed

Failed Example 1

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This a element positioned off screen is part of the sequential focus navigation using the keyboard.

<div aria-hidden="true">
	<a href="/" style="position:absolute; top:-999em">Link</a>
</div>

Failed Example 2

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This input element is part of the sequential focus navigation because it was incorrectly disabled.

<div aria-hidden="true">
	<input aria-disabled="true" />
</div>

Failed Example 3

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This button element is part of the sequential focus navigation and a descendant of an element with an aria-hidden attribute value of true because aria-hidden can’t be reset once set to true on an ancestor.

<div aria-hidden="true">
	<div aria-hidden="false">
		<button>Some button</button>
	</div>
</div>

Failed Example 4

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This p element is part of the sequential focus navigation because of the tabindex attribute.

<p tabindex="0" aria-hidden="true">Some text</p>

Failed Example 5

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This summary element is part of the sequential focus navigation.

<details aria-hidden="true">
	<summary>Some button</summary>
	<p>Some details</p>
</details>

Inapplicable

Inapplicable Example 1

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This aria-hidden attribute is ignored with null value.

<button tabindex="-1" aria-hidden>Some button</button>

Inapplicable Example 2

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This aria-hidden attribute is ignored with value false.

<p aria-hidden="false">Some text</p>

Inapplicable Example 3

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This aria-hidden attribute has an incorrect value.

<div aria-hidden="yes">
	<p>Some text</p>
</div>

Glossary

Attribute value

The attribute value of a content attribute set on an HTML element is the value that the attribute gets after being parsed and computed according to specifications. It may differ from the value that is actually written in the HTML code due to trimming whitespace or non-digits characters, default values, or case-insensitivity.

Some notable case of attribute value, among others:

• For enumerated attributes, the attribute value is either the state of the attribute, or the keyword that maps to it; even for the default states. Thus <input type="image" /> has an attribute value of either Image Button (the state) or image (the keyword mapping to it), both formulations having the same meaning; similarly, “an input element with a type attribute value of Text” can be either <input type="text" />, <input /> (missing value default), or <input type="invalid" /> (invalid value default).
• For boolean attributes, the attribute value is true when the attribute is present and false otherwise. Thus <button disabled>, <button disabled="disabled"> and <button disabled=""> all have a disabled attribute value of true.
• For attributes whose value is used in a case-insensitive context, the attribute value is the lowercase version of the value written in the HTML code.
• For attributes that accept numbers, the attribute value is the result of parsing the value written in the HTML code according to the rules for parsing this kind of number.
• For attributes that accept sets of tokens, whether space separated or comma separated, the attribute value is the set of tokens obtained after parsing the set and, depending on the case, converting its items to lowercase (if the set is used in a case-insensitive context).
• For aria-* attributes, the attribute value is computed as indicated in the WAI-ARIA specification and the HTML Accessibility API Mappings.

This list is not exhaustive, and only serves as an illustration for some of the most common cases.

The attribute value of an IDL attribute is the value returned on getting it. Note that when an IDL attribute reflects a content attribute, they have the same attribute value.

Focusable

An element is focusable if one or both of the following are true:

• the element is part of sequential focus navigation; or
• the element has a tabindex value that is not null.

Exception: Elements that lose focus during a period of up to 1 second after gaining focus, without the user interacting with the page the element is on, are not considered focusable.

Notes:

• The 1 second time span is an arbitrary limit which is not included in WCAG. Given that scripts can manage the focus state of elements, testing the focusability of an element consistently would be impractical without a time limit.
• The tabindex value of an element is the value of the tabindex attribute parsed using the rules for parsing integers. For the tabindex value to be different from null, it needs to be parsed without errors.

Included in the accessibility tree

Elements included in the accessibility tree of platform specific accessibility APIs are exposed to assistive technologies. This allows users of assistive technology to access the elements in a way that meets the requirements of the individual user.

The general rules for when elements are included in the accessibility tree are defined in the core accessibility API mappings. For native markup languages, such as HTML and SVG, additional rules for when elements are included in the accessibility tree can be found in the HTML accessibility API mappings (working draft) and the SVG accessibility API mappings (working draft).

For more details, see examples of included in the accessibility tree.

Programmatically hidden elements are removed from the accessibility tree. However, some browsers will leave focusable elements with an aria-hidden attribute set to true in the accessibility tree. Because they are hidden, these elements are considered not included in the accessibility tree. This may cause confusion for users of assistive technologies because they may still be able to interact with these focusable elements using sequential keyboard navigation, even though the element should not be included in the accessibility tree.

Outcome

An outcome is a conclusion that comes from evaluating an ACT Rule on a test subject or one of its constituent test target. An outcome can be one of the three following types:

• Inapplicable: No part of the test subject matches the applicability
• Passed: A test target meets all expectations
• Failed: A test target does not meet all expectations

Note: A rule has one passed or failed outcome for every test target. When there are no test targets the rule has one inapplicable outcome. This means that each test subject will have one or more outcomes.

Note: Implementations using the EARL10-Schema can express the outcome with the outcome property. In addition to passed, failed and inapplicable, EARL 1.0 also defined an incomplete outcome. While this cannot be the outcome of an ACT Rule when applied in its entirety, it often happens that rules are only partially evaluated. For example, when applicability was automated, but the expectations have to be evaluated manually. Such “interim” results can be expressed with the incomplete outcome.

Programmatically Hidden

An HTML element is programmatically hidden if either it has a computed CSS property visibility whose value is not visible; or at least one of the following is true for any of its inclusive ancestors in the flat tree:

• has a computed CSS property display of none; or
• has an aria-hidden attribute set to true

Note: Contrary to the other conditions, the visibility CSS property may be reverted by descendants.

Note: The HTML standard suggests setting the CSS display property to none for elements with the hidden attribute. While not required by HTML, all modern browsers follow this suggestion. Because of this the hidden attribute is not used in this definition. In browsers that use this suggestion, overriding the CSS display property can reveal elements with the hidden attribute.

Implementations

This section is not part of the official rule. It is populated dynamically and not accounted for in the change history or the last modified date.

Changelog

This is the first version of this ACT rule.