No keyboard trap non-standard navigation

  • Rule Typeatomic
  • Rule ID: ebe86a
  • Last modified: Jul 22, 2019
  • Accessibility Requirements Mapping
    • This rule is not required for conformance
  • Used in rules
  • Input Aspects

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

The 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 fulfil 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

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"
	class="target"
	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"
	class="target"
	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" class="target" 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"
	class="target"
	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"
	class="target"
	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" class="target" 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

Included in the accessibility tree

key: included-in-the-accessibility-tree

Elements included in the accessibility tree of platform specific accessibility APIs. Elements in the accessibility tree are exposed to assistive technologies, allowing users to interact with the elements in a way that meet 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 (work in progress) and the SVG accessibility API mappings (work in progress).

Note: Users of assistive technologies might still be able to interact with elements that are not included in the accessibility tree. An example of this is a focusable element with an aria-hidden attribute with a value of true. Such an element could still be interacted with using sequential keyboard navigation regardless of the assistive technologies used, even though the element would not be included in the accessibility tree.

Outcome

key: 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 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: Implementers 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

key: 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 behaviour 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

key: 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.


Changelog

Jul 22, 2019Replace useless visible-on-the-page with visible (#694)
Jul 19, 2019chore: run prettier (#688)
May 9, 2019Chore: Adapt site to ACT Rules CR format (#547)
May 7, 2019Template update - No keyboard trap non-standard navigation (#523)
Apr 29, 2019chore: rename files and update associations (#489)
Apr 16, 2019chore: add unique id to all rules (#478)
Apr 15, 2019chore: WCAG ACT RULES CG Website Update (#437)
Mar 3, 2019fix: update rule type frontmatter (#427)
Oct 24, 2018Keyboard trap - Editorial changes (#318)
Oct 12, 2018"Included in accessibility tree" instead of "exposed to assistive technologies" (#269)
Oct 5, 2018Consistency in test case headings
Oct 5, 2018Styling fixed in SC2-1-2-no-keyboard-trap-non-...
Sep 21, 2018Update SC2-1-2-no-keyboard-trap-non-standard-navigation.md
Aug 30, 2018Chore: Update test cases format and descriptions (#230)
Aug 8, 2018Rule: SC2-1-2-no-keyboard-trap-standard-navigation and SC2-1-2-no-keyboard-trap-non-standard-navigation (#171)
Jun 13, 2018Minor format changes
Jun 13, 2018Updated after review from Wilco and jkodu
Jun 13, 2018Update SC2-1-2-no-keyboard-trap-non-standard-navigation.md
May 24, 2018Updated testcases
May 24, 2018Create SC2-1-2-no-keyboard-trap-non-standard-navigation.md
May 24, 2018Rename SC2-1-2-no-keyboard-trap-standard-navigation to SC2-1-2-no-keyboard-trap-standard-navigation.md
May 24, 2018Rename SC2-1-2-no-keyboard-trap-r1.md to SC2-1-2-no-keyboard-trap-standard-navigation
May 24, 2018Update SC2-1-2-no-keyboard-trap-r1.md
Apr 5, 2018added rule SC2-1-2-no-keyboard-trap-r1

Useful Links



Acknowledgements