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Proposed Orientation of the page is not restricted using CSS transforms

Description

This rule checks that page content is not restricted to either landscape or portrait orientation using CSS transforms

Applicability

This rule applies to any HTML element that is visible and has one of the following CSS properties applied conditionally on the orientation media feature with a value of landscape or portrait:

Note: These specific transformation functions are of interest to this rule as they have the potential to affect the rotation of a given element.

Note: The rotate property and the rotate3d, rotateZ and matrix3d transform functions are currently part of a W3C Working Draft and widely implemented in browsers.

Expectation

The target element is neither rotated clockwise nor counter clockwise around the Z-axis at an angle corresponding to 90 degrees relative from the position of the element in landscape orientation to the position of the element in portrait orientation, and vice versa.

Note: Imagine the display of a smartphone with cartoon figure at its center. With this example, if a user turns the smartphone a quarter turn, that is a partial move from one orientation to the other, the user would expect that the cartoon figure continues to remain facing upwards. The smartphone accomplishes this by rotating the contents of its display a quarter turn to counter the users change in orientation. In effect, the cartoon figure has remained in place and its rotation relative from one orientation to the other is 0 degrees. Now imagine that a developer facilitated this rotation of the cartoon figure by a quarter turn only when the smartphone starts from one orientation and not the other; its rotation relative from one orientation to the other would then be 90 degrees and it would appear stuck, or locked, as the user moves between orientations. What the developer has done is effectively counter the smartphone’s attempt at countering the user’s change in orientation.

Assumptions

This rule does not consider and may produce incorrect results for:

Accessibility Support

There are no accessibility support issues known.

Background

Bibliography

Accessibility Requirements Mapping

Input Aspects

The following aspects are required in using this rule.

Test Cases

Passed

Passed Example 1

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A page where CSS transform property has rotateZ transform function conditionally applied on the orientation media feature which does not restrict the element to either portrait or landscape orientation.

<html lang="en">
	<head>
		<title>Page with some content</title>
		<style>
			@media (orientation: portrait) {
				html {
					transform: rotateZ(1turn);
				}
			}
		</style>
	</head>
	<body>
		<main>
			Page Content
		</main>
	</body>
</html>

Passed Example 2

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A page where CSS transform property has matrix transform function conditionally applied on the orientation media feature which does not restrict the element to either portrait or landscape orientation.

Note: The extremely small number in the transform function below is included to ensure testing methodologies correctly interpret the impacts of the transformation and are not simply looking for 0.

<html lang="en">
	<head>
		<title>Page with some content</title>
		<style>
			@media (orientation: portrait) {
				html {
					transform: matrix(1, -1.22465e-15, 1.22465e-15, 1, 0, 0);
				}
			}
		</style>
	</head>
	<body>
		<main>
			Page Content
		</main>
	</body>
</html>

Passed Example 3

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A page where the CSS rotate property has a 0 degree rotation conditionally applied on the orientation media feature which does not restrict the element to either portrait or landscape orientation.

<html lang="en">
	<head>
		<title>Page with some content</title>
		<style>
			@media (orientation: portrait) {
				html {
					rotate: 0turn;
				}
			}
		</style>
	</head>
	<body>
		<main>
			Page Content
		</main>
	</body>
</html>

Failed

Failed Example 1

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A page where CSS transform property has rotate transform function conditionally applied on the orientation media feature which restricts the element to landscape orientation.

<html lang="en">
	<head>
		<title>Page with some content</title>
		<style>
			@media (orientation: portrait) {
				html {
					transform: rotate(1.5708rad);
				}
			}
		</style>
	</head>
	<body>
		Page Content
	</body>
</html>

Failed Example 2

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A page where CSS transform property has matrix3d transform function conditionally applied on the orientation media feature which restricts the element to portrait orientation.

<html lang="en">
	<head>
		<title>Page with some content</title>
		<style>
			@media (orientation: landscape) {
				body {
					transform: matrix3d(0, -1, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1);
				}
			}
		</style>
	</head>
	<body>
		Page Content
	</body>
</html>

Failed Example 3

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This page appears rotated at a slight angle of 2.5 degrees for stylistic purposes, but is locked in portrait orientation by applying a 92.5 degree rotation when in landscape orientation:

<html lang="en">
	<head>
		<title>Page with some content</title>
		<style>
			body {
				transform: rotate(2.5deg);
			}

			@media (orientation: landscape) {
				body {
					transform: rotate(92.5deg);
				}
			}
		</style>
	</head>
	<body>
		Page Content
	</body>
</html>

Failed Example 4

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A page where the CSS rotate property has a 90 degree rotation conditionally applied on the orientation media feature which restricts the element to landscape orientation.

<html lang="en">
	<head>
		<title>Page with some content</title>
		<style>
			@media (orientation: portrait) {
				html {
					rotate: 90deg;
				}
			}
		</style>
	</head>
	<body>
		Page Content
	</body>
</html>

Inapplicable

Inapplicable Example 1

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A page where there are no CSS styles.

<html lang="en">
	<head>
		<title>Page with some content</title>
	</head>
	<body>
		I am a page with no styles
	</body>
</html>

Inapplicable Example 2

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A page that has no CSS transform property specified.

<html lang="en">
	<head>
		<title>Page with some content</title>
		<style>
			html {
				font-size: 22px;
			}
			@media (min-width: 30em) {
				font-size: 100%;
			}
		</style>
	</head>
	<body>
		Page Content
	</body>
</html>

Inapplicable Example 3

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A page where CSS transform property is applied to an element that is not visible.

<html lang="en">
	<head>
		<title>Page with some content</title>
		<style>
			@media (orientation: lanscape) {
				body {
					transform: rotateZ(0, 0, 1, 270deg);
				}
			}
		</style>
	</head>
	<body style="display:none;">
		<main>
			Page Content
		</main>
	</body>
</html>

Inapplicable Example 4

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A page where CSS transform property is not applied conditionally on the orientation media feature.

<html lang="en">
	<head>
		<title>Page with some content</title>
		<style>
			body {
				transform: rotate(90deg);
			}
		</style>
	</head>
	<body>
		<main>
			Page Content
		</main>
	</body>
</html>

Inapplicable Example 5

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A page where CSS transform property is conditionally applied on the orientation media feature, but does not have any of the applicable transformation functions which restricts the element to either landscape or portrait orientation.

<html lang="en">
	<head>
		<title>Page with some content</title>
		<style>
			@media (orientation: portrait) {
				body {
					transform: translateX(100px);
				}
			}
		</style>
	</head>
	<body>
		<main>
			Page Content
		</main>
	</body>
</html>

Glossary

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:

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.

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.

Rule Versions

This is the first version of this ACT rule.

Implementations

This section is not part of the official rule. It is populated dynamically and not accounted for in the change history or the last modified date.

Implementation Type Consistency Report
Alfa (fully automated) 0.57.2 Automated tool Consistent Alfa (fully automated) Report
Alfa (semi-automated) 0.57.2 Semi-automated tool Consistent Alfa (semi-automated) Report
Equal Access Accessibility Checker 3.1.42-rc.0 Automated tool Partial Equal Access Accessibility Checker Report
QualWeb 3.0.0 Automated tool Partial QualWeb Report
SortSite 6.45 Automated tool Consistent SortSite Report
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