Proposed Test Rule: 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.

Note: This rule only applies to HTML and SVG. Thus, it is a partial check for WCAG 2.0 success criterion 2.1.2, which applies to all content.

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

It is not possible to use unmodified arrow or tab keys, or other standard exit methods to move focus away.
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.

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

Keyboard trap with help information in a paragraph before, and where the method advised works.

<script>
	var trapOn = false
</script>

<p>Press the M-key to Exit</p>
<a id="link1" href="#">Link 1</a>
<button id="btn1" onblur="(function(e){trapOn=true; document.getElementById('btn2').focus();})(event)">
	Button 1
</button>
<button
	id="btn2"
	onkeydown="(function(e){ if (e.keyCode === 77){trapOn=false;document.getElementById('link2').focus();}})(event)"
	onblur="(function(e){ if(trapOn){document.getElementById('btn1').focus();}})(event)"
>
	Button 2
</button>
<a id="link2" href="#">Link 2</a>

Passed Example 2

Keyboard trap with help information within the trap, and where the method advised works.

<script>
	var trapOn = false
</script>

<a id="link1" href="#">Link 1</a>
<button id="btn1" onblur="(function(e){trapOn=true; document.getElementById('btn2').focus();})(event)">
	Button 1
</button>
<p>Press the M-key to Exit</p>
<button
	id="btn2"
	onkeydown="(function(e){ if (e.keyCode === 77){trapOn=false;document.getElementById('link2').focus();}})(event)"
	onblur="(function(e){ if(trapOn){document.getElementById('btn1').focus();}})(event)"
>
	Button 2
</button>
<a id="link2" href="#">Link 2</a>

Passed Example 3

Keyboard trap with “help” link that once clicked exposes the instructions.

<script>
	var trapOn = false

	function showHelpText() {
		document.getElementById('helptext').innerHTML = '<p>Press the M-key to Exit</p>'
	}
</script>

<div onkeydown="(function(e){ if (e.keyCode === 77){trapOn=false;document.getElementById('link2').focus();}})(event)">
	<a id="link1" href="#">Link 1</a>
	<button id="btn1" onblur="(function(e){trapOn=true; document.getElementById('helpLink').focus();})(event)">
		Button 1
	</button>
	<a id="helpLink" href="#" onclick="showHelpText()">How to go the next element</a>
	<div id="helptext"></div>
	<button id="btn2" onblur="(function(e){ if(trapOn){document.getElementById('btn1').focus();}})(event)">
		Button 2
	</button>
</div>
<a id="link2" href="#">Link 2</a>

Failed

Failed Example 1

Keyboard trap with no instructions.

<script>
	var trapOn = false
</script>

<a id="link1" href="#">Link 1</a>
<button id="btn1" onblur="(function(e){trapOn=true; document.getElementById('btn2').focus();})(event)">
	Button 1
</button>
<button
	id="btn2"
	onkeydown="(function(e){ if (e.keyCode === 77){trapOn=false;document.getElementById('link2').focus();}})(event)"
	onblur="(function(e){ if(trapOn){document.getElementById('btn1').focus();}})(event)"
>
	Button 2
</button>
<a id="link2" href="#">Link 2</a>

Failed Example 2

Keyboard trap with instructions that doesn’t give advise on the method for proceeding.

<script>
	var trapOn = false
</script>

<p>Go to the next element</p>
<a id="link1" href="#">Link 1</a>
<button id="btn1" onblur="(function(e){trapOn=true; document.getElementById('btn2').focus();})(event)">
	Button 1
</button>
<button
	id="btn2"
	onkeydown="(function(e){ if (e.keyCode === 77){trapOn=false;document.getElementById('link2').focus();}})(event)"
	onblur="(function(e){ if(trapOn){document.getElementById('btn1').focus();}})(event)"
>
	Button 2
</button>
<a id="link2" href="#">Link 2</a>

Failed Example 3

Keyboard trap with help text, where the method advised doesn’t work.

<script>
	var trapOn = false
</script>

<a id="link1" href="#">Link 1</a>
<button id="btn1" onblur="(function(e){trapOn=true; document.getElementById('btn2').focus();})(event)">
	Button 1
</button>
<p>Press the M-key to Exit</p>
<button id="btn2" onblur="(function(e){ if(trapOn){document.getElementById('btn1').focus();}})(event)">
	Button 2
</button>
<a id="link2" href="#">Link 2</a>

Inapplicable

Inapplicable Example 1

Not a keyboard trap (interactive element).

<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

Elements that can become the target of keyboard input as described in the HTML specification of focusable and can be focused.

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:

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.

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:

has a hidden attribute; or
has a computed CSS property display of none; or
has an aria-hidden attribute set to true

Note: Contrarily to the other conditions, the visibility CSS property may be reverted by descendants.

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.

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.