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Proposed Device motion based changes to the content can be disabled

Description

This rule checks that it is possible to disable any changes to the content of the web page resulting from device motion based events.

Applicability

This rule applies to an HTML document with an associated Window object that has an event listener list with one or more event listeners for device orientation events or device motion events.

Expectation

For each registered device orientation event or device motion event in the test target at least one of the following is true:

Background

The instruments used to pass this rule (if any), must meet all level A Success Criteria in order to fully satisfy Success Criterion 2.5.4: Motion Actuation. These extra requirements are left out of this rule, and should be tested separately.

Assumptions

Accessibility Support

There are no accessibility support issues known.

Bibliography

Accessibility Requirements Mapping

Input Aspects

The following aspects are required in using this rule.

Test Cases

This Javascript file is used in several examples:

File /test-assets/7677a9/slider.js:

function changeSlider(amount) {
	document.getElementById('motionSlider').value += amount
	document.getElementById('output').innerHTML = document.getElementById('motionSlider').value
}

function increaseSlider() {
	changeSlider(+1)
}

function decreaseSlider() {
	changeSlider(-1)
}

function applyChange(gamma, threshold) {
	if (gamma > threshold) {
		increaseSlider()
	} else if (gamma < -threshold) {
		decreaseSlider()
	}
}

function handleOrientation(event) {
	applyChange(event.gamma, 20)
}

function handleOrientationCanBeDisabled(event) {
	const disableMotion = document.getElementById('disableMotion')
	if (!disableMotion.checked) {
		applyChange(event.gamma, 20)
	}
}

function handleMotion(event) {
	applyChange(event.rotationRate.gamma, 5)
}

function handleMotionCanBeDisabled(event) {
	const disableMotion = document.getElementById('disableMotion')
	if (!disableMotion.checked) {
		applyChange(event.rotationRate.gamma, 5)
	}
}

Passed

Passed Example 1

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This HTML document has device orientation events that cause no changes to the content of the web page.

<html>
	<head>
		<title>Passed Example 1</title>
		<script>
			function activateEvent() {
				let counter = 0
				window.addEventListener('deviceorientation', () => {
					counter++
				})
			}
		</script>
	</head>

	<body onload="activateEvent();">
		<p>ACT-R</p>
		<p>Note: This example may not work across all browsers.</p>
	</body>
</html>

Passed Example 2

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This HTML document that can be operated through the device’s orientation to increase and decrease the value of a slider has a control to disable that functionality.

<html>
	<head>
		<title>Passed Example 2</title>
		<script src="/test-assets/7677a9/slider.js"></script>
		<script>
			function activateSlider() {
				window.addEventListener('deviceorientation', handleOrientationCanBeDisabled)
			}
		</script>
	</head>

	<body onload="activateSlider();">
		<h1>Slider Motion Sensor Example</h1>

		<p>
			Open this slider on a device with a motion sensor, such as a smartphone or tablet. Tilt the device to the right
			and left to adjust the slider value. The check box disables the motion sensing adjustment.
		</p>
		<p>Note: This example may not work across all browsers.</p>

		<div>
			<input type="range" min="1" max="100" value="50" id="motionSlider" disabled />
			<p aria-live="polite">Slider Value: <span id="output">50</span></p>
		</div>
		<div>
			<input type="checkbox" id="disableMotion" />
			<label for="disableMotion">Disable Motion Actuation</label>
		</div>
	</body>
</html>

Passed Example 3

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This HTML document that can be operated by rotating the device to increase and decrease the value of a slider has a control to disable that functionality.

<html>
	<head>
		<title>Passed Example 3</title>
		<script src="/test-assets/7677a9/slider.js"></script>
		<script>
			function activateSlider() {
				window.addEventListener('devicemotion', handleMotionCanBeDisabled)
			}
		</script>
	</head>

	<body onload="activateSlider();">
		<h1>Slider Motion Sensor Example</h1>

		<p>
			Open this slider on a device with a motion sensor, such as a smart phone or tablet. Rotate the device to adjust
			the slider value. The check box disables the motion sensing adjustment.
		</p>
		<p>Note: This example may not work across all browsers.</p>

		<div>
			<input type="range" min="1" max="100" value="50" id="motionSlider" disabled />
			<p aria-live="polite">Slider Value: <span id="output">50</span></p>
		</div>
		<div>
			<input type="checkbox" id="disableMotion" />
			<label for="disableMotion">Disable Motion Actuation</label>
		</div>
	</body>
</html>

Failed

Failed Example 1

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This HTML document that can be operated through the device’s orientation to increase and decrease the value of a slider but has no way to disable this functionality.

<html>
	<head>
		<title>Failed Example 1</title>
		<script src="/test-assets/7677a9/slider.js"></script>
		<script>
			function activateSlider() {
				window.addEventListener('deviceorientation', handleOrientation)
			}
		</script>
	</head>

	<body onload="activateSlider();">
		<pre class="output"></pre>

		<h1>Slider Motion Sensor Example</h1>

		<p>
			Open this slider on a device with a motion sensor, such as a smartphone or tablet. Tilt the device to the right
			and left to adjust the slider value.
		</p>
		<p>Note: This example may not work across all browsers.</p>

		<div>
			<input type="range" min="1" max="100" value="50" id="motionSlider" disabled />
			<button id="increaseSlider" type="button">Increase Value</button>
			<p aria-live="polite">Slider Value: <span id="output">50</span></p>
		</div>
	</body>
</html>

Inapplicable

Inapplicable Example 1

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This HTML document is not operable by device motion.

<p>ACT-Rules</p>

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 and do not regain 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.

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

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 five following types:

Note: A rule has one passed or failed outcome for every test target. When a tester evaluates a test target it can also be reported as cantTell if the rule cannot be tested in its entirety. For example, when applicability was automated, but the expectations have to be evaluated manually.

When there are no test targets the rule has one inapplicable outcome. If the tester is unable to determine whether there are test targets there will be one cantTell outcome. And when no evaluation has occurred the test target has one untested outcome. This means that each test subject always has one or more outcomes.

Outcomes used in ACT Rules can be expressed using the outcome property of the [EARL10-Schema][].

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.

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/.