Proposed Focusable element has no keyboard trap via standard navigation

Description

This rule checks if it is possible to use standard keyboard navigation to navigate through all content on a web page without becoming trapped in any element.

Applicability

This rule applies to any HTML or SVG element that is focusable.

Expectation

For each target element, focus can cycle to the browser UI by using standard keyboard navigation.

Note: It is not possible to fulfill this expectation by using browser specific shortcuts to return to the browser UI.

Background

This rule only requires navigation in one direction (either forward or backward), not both, and not a specific one. It is clear that not being able to escape a focus trap in any direction is a failure of Success Criterion 2.1.2 No keyboard trap. However, it is less clear that being able to escape in only one direction is enough to satisfy it. If Success Criterion 2.1.2 No keyboard trap requires the possibility to escape the trap in a specific way (e.g. forward standard keyboard navigation) or in both directions, this rule may pass while the criterion is not satisfied.

Assumptions

• The focus order in keyboard navigation is cyclical, not linear, meaning that the focus order will cycle to the first/last element when it moves away from the last/first element.
• The Browser UI is part of the focus navigation cycle of the page.

Accessibility Support

Some browsers have settings that will immediately cycle focus back to the web document. This fulfills the expectation because focus can cycle to the browser UI and the browser UI cycles focus back to the web document.

Bibliography

• Understanding Success Criterion 2.1.2: No Keyboard Trap
• G21: Ensuring that users are not trapped in content
• F10: Failure of Success Criterion 2.1.2 and Conformance Requirement 5 due to combining multiple content formats in a way that traps users inside one format type

Accessibility Requirements Mapping

This rule is not required for conformance.

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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These focusable elements do not create a trap for keyboard navigation.

<a href="#">Link 1</a> <button>Button1</button>

Passed Example 2

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This element is made focusable by the tabindex attribute. It does not create a trap for keyboard navigation.

<div role="button" tabindex="1">Text</div>

Passed Example 3

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This element is made focusable by the tabindex attribute, even if it is not part of the sequential focus navigation. It does not create a trap for keyboard navigation.

<div tabindex="-1">Text</div>

Passed Example 4

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While the elements with id “sentinelBefore” and “sentinelAfter” contain focus to the contents of the div with name “Sample Modal”, focus is not trapped since the user can use standard keyboard navigation using the Escape key or by activating the “Close button” to dismiss the modal

<div>Main page content with <a href="#">some link</a></div>
<div aria-hidden="true">
    <a href="#" id="sentinelBefore" style="position:absolute; top:-999em"
        >Upon receiving focus, this focus sentinel should wrap focus to the bottom of the modal</a
    >
</div>
<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>
    window.addEventListener('load', () => {
        document.getElementById('dialogFirst').focus();
    })
    document.getElementById('sentinelBefore').addEventListener('focus', () => {
        document.getElementById('closeButton').focus()
    })
    document.getElementById('sentinelAfter').addEventListener('focus', () => {
        document.getElementById('dialogFirst').focus()
    })
    document.getElementById('closeButton').addEventListener('click', () => {
        document.getElementById('sampleModal').style.display = 'none'
    })
    document.getElementById('sampleModal').addEventListener('keydown', (evt) => {
        if (evt.key === "Escape") {
            document.getElementById('sampleModal').style.display = 'none';    
        }
    })
</script>

Failed

Failed Example 1

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This focusable element creates a keyboard trap bringing focus to the button. Note that if one of the links is removed, the focus may jump to the browser UI before the timeout expires, at which point the this.focus() trap cannot trigger anymore.

<a href="#">Link 1</a>
<button onblur="setTimeout(() => this.focus(), 10)">
	Button1
</button>
<a href="#">Link 2</a>

Failed Example 2

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These focusable button elements create a keyboard trap preventing the last button to be reached using the keyboard.

<button onblur="setTimeout(() => this.nextElementSibling.focus(), 10)">
	Button1
</button>
<button onblur="setTimeout(() => this.previousElementSibling.focus(), 10)">
	Button2
</button>
<button>
	Button3
</button>

Failed Example 3

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This button element is between other button elements creating keyboard traps.

<button onblur="setTimeout(() => this.focus(), 10)">Button 1</button>
<button>Button 2</button>
<button onblur="setTimeout(() => this.focus(), 10)">Button 3</button>

Inapplicable

Inapplicable Example 1

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There is no focusable element.

<h1>Page 1</h1>

Inapplicable Example 2

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There is no focusable element.

<button type="button" disabled>Click Me!</button>

Inapplicable Example 3

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There is no focusable element.

<button type="button" style="display:none;">Click Me!</button>

Inapplicable Example 4

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There is no focusable element.

<a href="#" style="visibility:hidden;">Link 1</a> <button style="visibility:hidden;">Button1</button>

Glossary

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 and do not regain 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.

Namespaced Element

An element with a specific namespaceURI value from HTML namespaces. For example an “SVG element” is any element with the “SVG namespace”, which is http://www.w3.org/2000/svg.

Namespaced elements are not limited to elements described in a specification. They also include custom elements. Elements such as a and title have a different namespace depending on where they are used. For example a title in an HTML page usually has the HTML namespace. When used in an svg element, a title element has the SVG namespace instead.

Outcome

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 five 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
• cantTell: Whether the rule is applicable, or not all expectations were met could not be fully determined by the tester.
• Untested: The tester has not attempted to evaluate the test subject.

Note: A rule has one passed or failed outcome for every test target. When a tester evaluates a test target it can also be reported as cantTell if the rule cannot be tested in its entirety. For example, when applicability was automated, but the expectations have to be evaluated manually.

When there are no test targets the rule has one inapplicable outcome. If the tester is unable to determine whether there are test targets there will be one cantTell outcome. And when no evaluation has occurred the test target has one untested outcome. This means that each test subject always has one or more outcomes.

Outcomes used in ACT Rules can be expressed using the outcome property of the [EARL10-Schema][].

Standard keyboard navigation

Standard keyboard navigation entails using one or more of the following:

• Tab key
• Shift+Tab
• Arrow keys
• Esc key
• Enter key
• Space key

Expected behavior of standard keyboard navigation keys:

• Tab key: Skipping forward between focusable elements
• Shift+Tab: Skipping backwards between focusable elements
• Arrow keys: Navigate input elements, e.g. up/down drop down, between radio buttons etc.
• Esc key: Close or cancel, e.g close a modal
• Enter key: Select or activate the element in focus (same as clicking with mouse)
• Space key: Select input elements, e.g. drop downs, radio buttons etc.

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
Trusted Tester 5.1	Test methodology	Partial

Useful Links

• Github issues related to this rule
• Open a new issue
• Propose a change to the rule