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: Cycling back to the browser UI can be done both by moving forward through the tab order and by moving backwards. It is not possible to fulfill this expectation by using browser specific shortcuts to return to the browser UI.

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

There are no major accessibility support issues known for this rule.

Background

Bibliography

Accessibility Requirements Mapping

This rule is not required for conformance.

Input Aspects

The following aspects are required in using this rule.

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 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>

Failed

Failed Example 1

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This focusable element creates a keyboard trap bringing focus to the button.

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

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 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

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.

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.

Implementations

There are currently no known implementations for this rule. If you would like to contribute an implementation, please read the ACT Implementations page for details.

Changelog

This is the first version of this ACT rule.