Proposed Test Rule: 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 only applies to any HTML or SVG element that is focusable.
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
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 currently no assumptions.
Accessibility Support
There are no major accessibility support issues known for this rule.
Background
- 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
Test Cases
Passed
Passed Example 1
No trap for keyboard navigation.
<a href="#">Link 1</a> <button>Button1</button>
Passed Example 2
Using tabindex="1".
<div tabindex="1">Text</div>
Passed Example 3
Using tabindex="-1".
<div tabindex="-1">Text</div>
Passed Example 4
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 5
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 6
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 one element.
<a href="#">Link 1</a>
<button onblur="setTimeout(() => this.focus(), 10)">
Button1
</button>
Failed Example 2
Keyboard trap group.
<button onblur="setTimeout(() => this.nextElementSibling.focus(), 10)">
Button1
</button>
<button onblur="setTimeout(() => this.previousElementSibling.focus(), 10)">
Button2
</button>
<button>
Button3
</button>
Failed Example 3
A focusable element between keyboard traps.
<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
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 5
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 6
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
No focusable element.
<h1>Page 1</h1>
Inapplicable Example 2
Disabled element.
<button type="button" disabled>Click Me!</button>
Inapplicable Example 3
Hidden element using display:none.
<button type="button" style="display:none;">Click Me!</button>
Inapplicable Example 4
Hidden element using visibility:hidden.
<a href="#" style="visibility:hidden;">Link 1</a> <button style="visibility:hidden;">Button1</button>
Glossary
Focusable
Elements that can become the target of keyboard input as described in the HTML specification of focusable and can be focused.
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.
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.