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Proposed No keyboard shortcut uses only printable characters

Description

This rule checks that if keyboard shortcuts are implemented using only printable characters, then there is a mechanism to disable the shortcut, or to remap the shortcut to use one or more non-printable character keys, or the shortcut for a user interface component is only available when that component has focus.

Applicability

This rule applies to any keyboard event for which all of the following is true:

Expectation

For each test target at least one of the following is true:

Assumptions

Accessibility Support

Currently keyboard events only support the types keydown and keyup. Keyboard events of type keypressed are considered legacy keyboard events and are thus ignored by this rule.

Background

The instruments used to pass this rule (if any), must meet all level A Success Criteria in order to fully satisfy Success Criterion 2.1.4: Character Key Shortcuts. These extra requirements are left out of this rule, and should be tested separately. This rule allows changes to the content when a user interface component has focus to meet the “Active only on focus” requirement from Success Criterion 2.1.4. As explained in the Event dispatch and DOM event flow section of the UI Events Working Draft, each keyboard event is dispatched to an event target. The event target is the element that has focus. As such, the “Active only on focus” requirement from Success Criterion 2.1.4 is implied by saying that the event target is an inheriting semantic widget.

The “Turn off” and “Remap” requirements from Success Criterion 2.1.4 are combined in the disable/remap item of the Expectation section. For the disable requirement, changes in content that are made through keyboard events with a printable character value for the key attribute and a getModifierState return value of false for each of the valid modifier keys effectively need to be blocked (in other words, turned off or disabled). The remap requirement unblocks the events if the getModifierState query returns true for at least one of the valid modifier keys. Once the getModifierState returns true for at least one of the valid modifier keys of a keyboard event, such keyboard event is no longer applicable for the rule and it passes the “Remap” requirement from Success Criterion 2.1.4.

Bibliography

Accessibility Requirements Mapping

Input Aspects

The following aspects are required in using this rule.

Test Cases

These Javascript and CSS files are used in several examples:

File /test-assets/ffbc54/shortcut.js:

const defaultParams = {
	target: 'target',
	focusOnly: false,
	shortcutKey: '',
	ctrlKey: false,
	disabled: false,
}

const shortcutDefinitions = new Array()

function activateShortcuts() {
	document.body.addEventListener('keydown', function(event) {
		for (const settings of shortcutDefinitions) {
			if (!settings.disabled) {
				const target = document.getElementById(settings.target)

				if (
					event.key === settings.shortcutKey &&
					(!settings.ctrlKey || event.getModifierState('Control')) &&
					(!settings.focusOnly || document.activeElement === target)
				) {
					document.getElementById('list').innerHTML += '<li>' + target.value + '</li>'
					target.value = ''
					event.preventDefault()
				}
			}
		}
	})
}

function registerShortcut(params = {}) {
	shortcutDefinitions.push({ ...defaultParams, ...params })
}

function changeShortcutParameter(id, param, value) {
	shortcutDefinitions.find(shortcut => shortcut.id === id)[param] = value
}

function toggleDisabled(id, value) {
	changeShortcutParameter(id, 'disabled', value)
}

function toggleModifier(id, value) {
	changeShortcutParameter(id, 'ctrlKey', value)
}

function openModal() {
	document.getElementById('overlay').style.display = 'block'
}
function closeModal() {
	document.getElementById('overlay').style.display = 'none'
}

File /test-assets/ffbc54/styles.css:

#overlay {
	display: none;
	position: fixed;
	top: 2em;
	left: 10em;
	background-color: #505050;
	color: white;
	padding: 1em;
	padding-top: 0em;
}

Passed

Passed Example 1

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This HTML document is listening to keyboard events for which the attribute key is a printable character and the method getModifierState returns false, and which cause changes in content. There exists an instrument to disable the keyboard event so that same key events are blocked unless getModifierState("Control") returns true, therefore meeting the disable/remap expectation.

<html>
	<head>
		<title>Passed Example 1</title>
		<script src="/test-assets/ffbc54/shortcut.js"></script>
	</head>
	<body onload="registerShortcut({id: 'singleShortcut', shortcutKey: '+'}); activateShortcuts();">
		<label for="target">Add to list (press "+" to add):</label>
		<input type="text" id="target" />
		<div>
			<div>Remap shortcut</div>
			<div>
				<label>
					<input id="remap" type="checkbox" onclick="toggleModifier('singleShortcut', this.checked)" />
					Use "ctrl" key together with the "+" key
				</label>
			</div>
		</div>
		<br />
		<div>
			To do list
		</div>
		<ul id="list"></ul>
	</body>
</html>

Passed Example 2

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This HTML document is listening to keyboard events for which the attribute key is a printable character and the method getModifierState returns false, and which cause changes in content. There exists an instrument to disable the keyboard event. A disabled event implies that the event is disabled when the getModifierState method returns false.

<html>
	<head>
		<title>Passed Example 2</title>
		<script src="/test-assets/ffbc54/shortcut.js"></script>
	</head>
	<body onload="registerShortcut({id: 'singleShortcut', shortcutKey: '+'}); activateShortcuts();">
		<label for="target">Add to list (press "+" to add):</label>
		<input type="text" id="target" />
		<label>
			<input type="checkbox" onclick="toggleDisabled('singleShortcut', !this.checked)" checked />
			Toggle single character keyboard shortcut
		</label>
		<br />
		<div>
			To do list
		</div>
		<ul id="list"></ul>
	</body>
</html>

Passed Example 3

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This HTML document is listening to keyboard events for which the attribute key is a printable character and the method getModifierState returns false, and which cause changes in content. For each keyboard event causing changes in content, there exists an instrument to disable it so that same key events are blocked unless getModifierState("Control") returns true, therefore meeting the disable/remap expectation.

<html>
	<head>
		<title>Passed Example 3</title>
		<script src="/test-assets/ffbc54/shortcut.js"></script>
	</head>
	<body
		onload="registerShortcut({id: 'firstShortcut', shortcutKey: '+'}); registerShortcut({id: 'secondShortcut', shortcutKey: 'a'}); activateShortcuts();"
	>
		<label for="target">Add to list (press "+" or "a" to add):</label>
		<input type="text" id="target" />
		<div>
			<div>Remap shortcut</div>
			<div>
				<label>
					<input id="remap1" type="checkbox" onclick="toggleModifier('firstShortcut', this.checked)" />
					Use "ctrl" key together with the "+" key
				</label>
				<label>
					<input id="remap2" type="checkbox" onclick="toggleModifier('secondShortcut', this.checked)" />
					Use "ctrl" key together with the "a" key
				</label>
			</div>
		</div>
		<br />
		<div>
			To do list
		</div>
		<ul id="list"></ul>
	</body>
</html>

Passed Example 4

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This HTML document is listening to keyboard events for which the attribute key is a printable character and the method getModifierState returns false, and which cause changes in content. There exists an instrument to disable those keyboard events that cause changes in content so that same key events are blocked unless getModifierState("Control") returns true. In this example, the same instrument is used to remap all keyboard events.

<html>
	<head>
		<title>Passed Example 4</title>
		<script src="/test-assets/ffbc54/shortcut.js"></script>
	</head>
	<body
		onload="registerShortcut({id: 'firstShortcut', shortcutKey: '+'}); registerShortcut({id: 'secondShortcut', shortcutKey: 'a'}); activateShortcuts();"
	>
		<label for="target">Add to list (press "+" or "a" to add):</label>
		<input type="text" id="target" />
		<div>
			<div>Remap shortcut</div>
			<div>
				<label>
					<input
						id="remap"
						type="checkbox"
						onclick="toggleModifier('firstShortcut', this.checked); toggleModifier('secondShortcut', this.checked);"
					/>
					Use "ctrl" key together with the "+" or "a" key
				</label>
			</div>
		</div>
		<br />
		<div>
			To do list
		</div>
		<ul id="list"></ul>
	</body>
</html>

Passed Example 5

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This HTML document is listening to keyboard events for which the attribute key is a printable character and the method getModifierState returns false, and which cause changes in content, but the events are blocked when no widget has focus.

<html>
	<head>
		<title>Passed Example 5</title>
		<script src="/test-assets/ffbc54/shortcut.js"></script>
	</head>

	<body onload="registerShortcut({shortcutKey: '+', focusOnly: true}); activateShortcuts();">
		<label for="target">Add to list (press "+" to add):</label>
		<input type="text" id="target" />
		<br />
		<div>
			To do list
		</div>
		<ul id="list"></ul>
	</body>
</html>

Passed Example 6

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This HTML document is listening to keyboard events for which the attribute key is a printable character and the method getModifierState returns false, and which cause changes in content. There exists a set of clearly labeled instruments to disable or to remap the keyboard event so that same key events are blocked unless getModifierState("Control") returns true.

<html>
	<head>
		<title>Passed Example 6</title>
		<link rel="stylesheet" type="text/css" href="/test-assets/ffbc54/styles.css" />
		<script src="/test-assets/ffbc54/shortcut.js"></script>
	</head>
	<body onload="registerShortcut({id: 'singleShortcut', shortcutKey: '+'}); activateShortcuts();">
		<div id="overlay">
			<p>Disable/remap shortcut</p>
			<label>
				<input type="checkbox" onclick="toggleDisabled('singleShortcut', !this.checked)" checked />
				Toggle single character keyboard shortcut
			</label>
			<br />
			<label>
				<input id="remap" type="checkbox" onclick="toggleModifier('singleShortcut', this.checked)" />
				Use "ctrl" key together with the "+" key
			</label>
			<br />
			<button onclick="closeModal();">Dismiss</button>
		</div>
		<p>To control the shortcuts activate the "Control shortcuts" button.</p>
		<input type="button" onclick="openModal()" value="Control shortcuts" />

		<label for="target">Add to list (press "+" to add):</label>
		<input type="text" id="target" />
		<div>
			To do list
		</div>
		<ul id="list"></ul>
	</body>
</html>

Failed

Failed Example 1

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This HTML document is listening to keyboard events for which the attribute key is a printable character and the method getModifierState returns false, and which cause changes in content. There is no instrument to disable or remap the keyboard event and the keyboard events are not blocked when no widget has focus.

<html>
	<head>
		<title>Failed Example 1</title>
		<script src="/test-assets/ffbc54/shortcut.js"></script>
	</head>
	<body onload="registerShortcut({shortcutKey: '+', disabled: false}); activateShortcuts();">
		<label for="target">Add to list (press "+" to add):</label>
		<input type="text" id="target" />
		<br />
		<div>
			To do list
		</div>
		<ul id="list"></ul>
	</body>
</html>

Failed Example 2

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This HTML document is listening to keyboard events for which the attribute key is a printable character and the method getModifierState returns false, and which cause changes in content. There is an instrument to disable or remap the keyboard event so that same key events are blocked unless getModifierState("Control") returns true, but the instrument is not in a clearly labeled location.

<html>
	<head>
		<title>Failed Example 2</title>
		<link rel="stylesheet" type="text/css" href="/test-assets/ffbc54/styles.css" />
		<script src="/test-assets/ffbc54/shortcut.js"></script>
	</head>
	<body onload="registerShortcut({id: 'singleShortcut', shortcutKey: '+'}); activateShortcuts();">
		<div id="overlay">
			<p>Disable/remap shortcut</p>
			<label>
				<input type="checkbox" onclick="toggleDisabled('singleShortcut', !this.checked)" checked />
				Toggle single character keyboard shortcut
			</label>
			<br />
			<label>
				<input id="remap" type="checkbox" onclick="toggleModifier('singleShortcut', this.checked)" />
				Use "ctrl" key together with the "+" key
			</label>
			<br />
			<button onclick="closeModal();">Dismiss</button>
		</div>

		<input type="button" onclick="openModal()" value="Open modal" />

		<label for="target">Add to list (press "+" to add):</label>
		<input type="text" id="target" />
		<div>
			To do list
		</div>
		<ul id="list"></ul>
	</body>
</html>

Inapplicable

Inapplicable Example 1

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This HTML document has a keyboard event dispatched to an event target but it only causes changes in content if the event’s attribute key is not a printable character (in this example, the Escape key).

<html>
	<head>
		<title>Inapplicable Example 1</title>
		<script src="/test-assets/ffbc54/shortcut.js"></script>
	</head>

	<body onload="registerShortcut({shortcutKey: 'Escape'}); activateShortcuts();">
		<label for="target">Add to list (press "esc" to add):</label>
		<input type="text" id="target" />
		<br />
		<div>
			To do list
		</div>
		<ul id="list"></ul>
	</body>
</html>

Inapplicable Example 2

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This HTML document has a keyboard event dispatched to an event target with the attribute key being a printable character but it does not cause changes in content unless the getModifierState returns true.

<html>
	<head>
		<title>Inapplicable Example 2</title>
		<script src="/test-assets/ffbc54/shortcut.js"></script>
	</head>

	<body onload="registerShortcut({shortcutKey: '+', ctrlKey: true}); activateShortcuts();">
		<label for="target">Add to list (press "ctrl" and "+" to add):</label>
		<input type="text" id="target" />
		<br />
		<div>
			To do list
		</div>
		<ul id="list"></ul>
	</body>
</html>

Glossary

Blocked event

A blocked event makes no changes to the content of the web page.

Changes in content

A event originated change in the content of a web page occurs when, by comparing the web page before and 1 minute after the event firing, at least one of the following occurs:

Assumptions:

Clearly labeled location

Secondary information and alternative controls of functionality are often not displayed together with primary information or functionality. For example, an option to change a web page to dark mode may be placed on an options page instead of being available on every page and page state of a website. Another example is a maps application, where, instead of using GPS, an option is available in a dropdown menu to set the current location of the device. Such content should be placed in a clearly labeled location.

The location of a target is said to be clearly labeled when the target can be found by activating “identifiable” instruments which either lead the user to find the target, or to another page or page state from which this action can be repeated until the target is found.

Whether or not the content is “clearly labeled” depends on the starting point of the search. If page A has a link which clearly “identifies” some piece of content, then the location of the content is clearly labeled. Page B, which can be in the same website, may not have such a link or may have a link with a link text that does not “identify” target content or which can be interpreted to “identify” more than one target, and so the location of the content starting from page B is not clearly labeled.

For the purpose of this definition, an instrument is identifiable if any text or other content with a text alternative, allows any user to identify an element with a semantic role that inherits from widget.

A web page changes state when the document’s body changes without a change in the document’s URL.

Explicit Semantic Role

The explicit semantic role of an element is determined by its role attribute (if any).

The role attribute takes a list of tokens. The explicit semantic role is the first valid role in this list. The valid roles are all non-abstract roles from WAI-ARIA Specifications. If the element has no role attribute, or if it has one with no valid role, then this element has no explicit semantic role.

Other roles may be added as they become available. Not all roles will be supported in all assistive technologies. Testers are encouraged to adjust which roles are allowed according to the accessibility support base line. For the purposes of executing test cases in all rules, it should be assumed that all roles are supported by assistive technologies so that none of the roles fail due to lack of accessibility support.

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:

Implicit Semantic Role

The implicit semantic role of an element is a pre-defined value given by the host language which depends on the element and its ancestors.

Implicit roles for HTML and SVG, are documented in the HTML accessibility API mappings (working draft) and the SVG accessibility API mappings (working draft).

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.

Inheriting Semantic Role

An element with an inheriting semantic role of X is any element with a non-abstract semantic role that inherits from X, or is the same as X.

Example: An “inheriting semantic link” is any element that either has the semantic role of link or a semantic role that inherits from the link role, such as doc-biblioref.

Instrument to achieve an objective

An HTML element that when activated allows an end-user to achieve an objective.

Note: Any rule that uses this definition must provide an unambiguous description of the objective the instrument is used to achieve.

Marked as decorative

An element is marked as decorative if one or more of the following conditions is true:

Elements are marked as decorative as a way to convey the intention of the author that they are pure decoration. It is different from the element actually being pure decoration as authors may make mistakes. It is different from the element being effectively ignored by assistive technologies as rules such as presentational roles conflict resolution may overwrite this intention.

Elements can also be ignored by assistive technologies if they are programmatically hidden. This is different from marking the element as decorative and does not convey the same intention. Notably, being programmatically hidden may change as users interact with the page (showing and hiding elements) while being marked as decorative should stay the same through all states of the page.

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.

Printable characters

A printable character is a character that occupies a printing position on a display.

These characters correspond to the following Unicode categories:

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.

Same key events

Two keyboard events are same key events if they have the same value for all the following attributes:

Semantic Role

The semantic role of an element is determined by the first of these cases that applies:

  1. Conflict If the element is marked as decorative, but the element is included in the accessibility tree; or would be included in the accessibility tree when it is not programmatically hidden, then its semantic role is its implicit role.
  2. Explicit If the element has an explicit role, then its semantic role is its explicit role.
  3. Implicit The semantic role of the element is its implicit role.

This definition can be used in expressions such as “semantic button” meaning any element with a semantic role of button.

Set of clearly labeled instruments

A set of clearly labeled instruments is a set of instruments, where each instrument is in the same web page as the test target or can be found in a clearly labeled location from that web page.

WAI-ARIA specifications

The WAI ARIA Specifications group both the WAI ARIA W3C Recommendation and ARIA modules, namely:

Note: depending on the type of content being evaluated, part of the specifications might be irrelevant and should be ignored.

Web page (HTML)

An HTML web page is the set of all fully active documents which share the same top-level browsing context.

Note: Nesting of browsing context mostly happens with iframe and object. Thus a web page will most of the time be a “top-level” document and all its iframe and object (recursively).

Note: Web pages as defined by WCAG are not restricted to the HTML technology but can also include, e.g., PDF or DOCX documents.

Note: Although web pages as defined here are sets of documents (and do not contain other kind of nodes), one can abusively write that any node is “in a web page” if it is a shadow-including descendant of a document that is part of that web page.

Rule Versions

This is the first version of this ACT rule.

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.

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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/.