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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.

Bibliography

Accessibility Requirements Mapping

Input Aspects

The following aspects are required in using this rule.

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 not focusable because it moves focus to the input element whenever it receives focus. These elements are sometimes referred to as ‘focus sentinel’ or ‘bumper’. They are typically found before and after a modal / dialog in order to contain focus within the modal. Page authors do not want the sentinel to be visible, nor do they want them to be read by a screen reader. But, they do want the element to be part of the sequential focus navigation. This allows the page author to detect that focus has left the dialog in order to wrap it to the top/bottom as appropriate.

<div id="sampleModal" role="dialog" aria-label="Sample Modal" aria-modal="true" style="border: solid black 1px; padding: 1rem;">
    <label>First and last name <input id="dialogFirst"></label><br />
    <button id="closeButton">Close button</button>
</div>
<div aria-hidden="true">
    <a href="#" id="sentinelAfter" style="position:absolute; top:-999em">Upon receiving focus, this focus sentinel should wrap focus to the top of the modal</a>
</div>
<script>
    document.getElementById("sentinelAfter").addEventListener("focus", () => {
        document.getElementById("dialogFirst").focus();
    });
    document.getElementById("closeButton").addEventListener("click", () => {
        document.getElementById("sampleModal").style.display = "none";
    });
</script>

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>

Failed Example 6

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This a element is focusable because it fails to move focus when it receives focus. This is in contrast to a focus sentinel that immediately jumps focus to a valid location. Focus sentinels are typically used before and after a modal dialog in order to contain and wrap focus. In this case, the focus event was removed, but the sentinel was not.

<div id="sampleModal" role="dialog" aria-label="Sample Modal" aria-modal="true" style="border: solid black 1px; padding: 1rem;">
    <label>First and last name <input id="dialogFirst"></label><br />
    <button id="closeButton">Close button</button>
</div>
<div aria-hidden="true">
    <a href="#" id="sentinelAfter" style="position:absolute; top:-999em">Upon receiving focus, this focus sentinel should wrap focus to the top of the modal</a>
</div>
<script>
    document.getElementById("closeButton").addEventListener("click", () => {
        document.getElementById("sampleModal").style.display = "none";
    });
</script>

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:

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:

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:

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:

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:

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.

Rule Versions

This is the first version of this ACT rule.

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.

Implementation Type Consistency Report
Alfa 0.36.0 Automated tool Partial Alfa Report
Axe DevTools Pro 4.24.5 Semi-automated tool Consistent Axe DevTools Pro Report
Axe-core 4.5.0-prerelease Automated tool Consistent Axe-core Report
Equal Access Accessibility Checker 3.1.33-rc Automated tool Partial Equal Access Accessibility Checker Report
QualWeb 3.0.0 Automated tool Partial QualWeb Report
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This is an unpublished draft preview that might include content that is not yet approved. The published website is at w3.org/WAI/.