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

Description

This rule checks if it is possible to use non-standard keyboard navigation to navigate through content where focus is trapped when using standard ways of keyboard navigation.

Applicability

This rule applies to any HTML or SVG element that is focusable where focus cannot cycle to the browser UI by using standard keyboard navigation.

Expectation 1

For each target element help information is visible and included in the accessibility tree or can be accessed from within the keyboard trap.

Note: As per WCAG 2.0 Success Criterion 2.1.1 Keyboard the help information should be accessible through a keyboard interface.

Expectation 2

The help information explains how to cycle to the browser UI, or on how to get to a point from where it is possible to cycle to the browser UI, using standard keyboard navigation.

Expectation 3

For each target element focus can cycle to the browser UI by using the method advised in the help information.

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

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 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 2

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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 3

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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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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 2

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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 3

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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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This focusable button elements do not create a keyboard trap.

<a id="link1" href="#">Link 1</a>
<button id="btn1">Button 1</button>
<button id="btn2">Button 2</button>
<a id="link2" href="#">Link 2</a>

Glossary

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.

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:

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.

Standard keyboard navigation

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

Expected behavior of standard keyboard navigation keys:

Visible

Content perceivable through sight.

Content is considered visible if making it fully transparent would result in a difference in the pixels rendered for any part of the document that is currently within the viewport or can be brought into the viewport via scrolling.

Content is defined in WCAG.

For more details, see examples of visible.

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.

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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/.