Proposed Focusable element has no keyboard trap

Description

This rule checks for keyboard traps. This includes use of both standard and non-standard keyboard navigation to navigate through all content without becoming trapped.

Applicability

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

Expectation

For each test target, the outcome of at least one of the following rules is “passed”:

• Focusable Element Has No Keyboard Trap Via Standard Navigation
• Focusable Element Has No Keyboard Trap Via Non-Standard Navigation

Assumptions

There are no assumptions.

Accessibility Support

There are no accessibility support issues known.

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.

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

• 2.1.2 No Keyboard Trap (Level A)

  • Learn more about 2.1.2 No Keyboard Trap
  • 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
• WCAG Non-Interference

  • Learn more about WCAG Non-Interference
  • Required for conformance to WCAG 2.1.
  • Outcome mapping:
    • Any failed outcomes: WCAG 2 conformance requirement is not satisfied
    • All passed outcomes: WCAG 2 conformance requirement needs further testing
    • An inapplicable outcome: WCAG 2 conformance requirement needs further testing
• G21: Ensuring that users are not trapped in content

  • Learn more about technique G21
  • Not required for conformance to any W3C accessibility recommendation.
  • Outcome mapping:
    • Any failed outcomes: technique is not satisfied
    • All passed outcomes: technique needs further testing
    • An inapplicable outcome: technique needs further testing

Input Rules

Outcomes of the following rules are required as input for this rule.

• Focusable element has no keyboard trap via standard navigation
• Focusable element has no keyboard trap via non-standard navigation

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>

Passed Example 4

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These focusable button elements have scripts that create a keyboard trap. The document includes help information in a paragraph before the button elements and the method advised works to escape the keyboard trap.

<script src="/test-assets/focusable-no-keyboard-trap/keyboard.js"></script>

<p>Press Ctrl+M to Exit</p>
<a id="link1" href="#">Link 1</a>
<button id="btn1" onfocus="trapOn = true" onblur="moveFocusToButton('btn2')" onkeydown="escapeTrapOnCtrlM(event)">
	Button 1
</button>
<button id="btn2" onfocus="trapOn = true" onblur="moveFocusToButton('btn1')" onkeydown="escapeTrapOnCtrlM(event)">
	Button 2
</button>
<a id="link2" href="#">Link 2</a>

Passed Example 5

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These focusable button elements have scripts that create a keyboard trap. The document includes help information within the trap and the method advised works to escape the keyboard trap.

<script src="/test-assets/focusable-no-keyboard-trap/keyboard.js"></script>

<a id="link1" href="#">Link 1</a>
<button id="btn1" onfocus="trapOn = true" onblur="moveFocusToButton('btn2')" onkeydown="escapeTrapOnCtrlM(event)">
	Button 1
</button>
<p>Press Ctrl+M to Exit</p>
<button id="btn2" onfocus="trapOn = true" onblur="moveFocusToButton('btn1')" onkeydown="escapeTrapOnCtrlM(event)">
	Button 2
</button>
<a id="link2" href="#">Link 2</a>

Passed Example 6

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These focusable button elements have scripts that create a keyboard trap. The document includes help information in a “help” link that once clicked exposes the instructions to escape the keyboard trap.

<script src="/test-assets/focusable-no-keyboard-trap/keyboard.js"></script>

<div onkeydown="escapeTrapOnCtrlM(event)">
	<a id="link1" href="#">Link 1</a>
	<button id="btn1" onfocus="trapOn = true" onblur="moveFocusTo('helpLink')">
		Button 1
	</button>
	<a id="helpLink" href="#" onclick="showHelpText()">How to go the next element</a>
	<div id="helptext"></div>
	<button id="btn2" onblur="moveFocusTo('btn1')">
		Button 2
	</button>
</div>
<a id="link2" href="#">Link 2</a>

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 a keyboard trap.

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

Failed Example 4

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These focusable button elements create a keyboard trap with no instructions.

<script src="/test-assets/focusable-no-keyboard-trap/keyboard.js"></script>

<a id="link1" href="#">Link 1</a>
<button id="btn1" onfocus="trapOn = true" onblur="moveFocusToButton('btn2')" onkeydown="escapeTrapOnCtrlM(event)">
	Button 1
</button>
<button id="btn2" onfocus="trapOn = true" onblur="moveFocusToButton('btn1')" onkeydown="escapeTrapOnCtrlM(event)">
	Button 2
</button>
<a id="link2" href="#">Link 2</a>

Failed Example 5

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These focusable button elements create a keyboard trap with instructions that don’t give advice on the method for proceeding.

<script src="/test-assets/focusable-no-keyboard-trap/keyboard.js"></script>

<p>Go to the next element</p>
<a id="link1" href="#">Link 1</a>
<button id="btn1" onfocus="trapOn = true" onblur="moveFocusToButton('btn2')" onkeydown="escapeTrapOnCtrlM(event)">
	Button 1
</button>
<button id="btn2" onfocus="trapOn = true" onblur="moveFocusToButton('btn1')" onkeydown="escapeTrapOnCtrlM(event)">
	Button 2
</button>
<a id="link2" href="#">Link 2</a>

Failed Example 6

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These focusable button elements create a keyboard trap with help text, where the method advised doesn’t work.

<script src="/test-assets/focusable-no-keyboard-trap/keyboard.js"></script>

<a id="link1" href="#">Link 1</a>
<button id="btn1" onfocus="trapOn = true" onblur="moveFocusToButton('btn2')">
	Button 1
</button>
<p>Press Ctrl+M to Exit</p>
<button id="btn2" onfocus="trapOn = true" onblur="moveFocusToButton('btn1')">
	Button 2
</button>
<a id="link2" href="#">Link 2</a>

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

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