ACT-Rules Community

Image not in the accessibility tree is decorative

  • Rule Type:atomic
  • Rule Id: e88epe
  • Last modified: Jan 11, 2022
  • Accessibility Requirements Mapping:
    • 1.1.1 Non-text Content (Level A)
      • Learn More about 1.1.1 Non-text Content
      • Required for conformance to WCAG 2.0 and later on level A and higher.
      • Outcome mapping:
        • Any failed outcomes: success criterion is not satisfied.
        • All passed outcomes: success criterion needs further testing.
        • An inapplicable outcome: success criterion needs further testing.
  • Input Aspects:

Description

This rule checks that visible img, svg and canvas elements that are ignored by assistive technologies are decorative.

Applicability

This rule applies to any img, canvas or svg element that is visible and for which at least one of the following is true:

Exception: This rule never applies to elements for which one or more of the following is true:

Note: An example of an image ignored because of an ancestor with named from author is when the image is a descendant of a button element that uses aria-label for its accessible name.

Expectation

Each test target is purely decorative.

Note: It is relatively common for an informative image such as an icon to be marked up as decorative, if the text alternative is adjacent to the image. This is a conforming alternative version for the image. This fails the rule but meets conformance requirement 1 of WCAG 2.1.

Assumptions

  • svg elements with a semantic role of graphics-document and with an empty ("") accessible name are ignored by assistive technologies tested for this rule. If some assistive technology does not ignore these elements, and that assistive technology is required for conformance, passing this rule does not ensure all decorative svg elements can be ignored, and the success criterion 1.1.1 Non-text content may still not be satisfied. The same is true for canvas elements with no semantic role and an empty ("") accessible name.
  • A web page with informative images without an accessible name may conform to WCAG 2.1 Level A when the information provided by that image is available elsewhere on the web page itself. For example if an equivalent text is adjacent to the image, or if the text alternative is included in the accessible name of a parent element.

Accessibility Support

No accessibility support issues known.

Background

Bibliography

Test Cases

Passed

Passed Example 1

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This img element with an empty alt attribute which is not included in the accessibility tree is purely decorative.

<p>Happy new year!</p>
<img src="/test-assets/shared/fireworks.jpg" alt="" />

Passed Example 2

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This img element that is ignored by assistive technologies because aria-hidden is set to true is purely decorative.

<p>Happy new year!</p>
<img src="/test-assets/shared/fireworks.jpg" aria-hidden="true" role="img" alt="" />

Passed Example 3

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This img element that is ignored by assistive technologies because it has an explicit semantic role of none is purely decorative.

<p>Happy new year!</p>
<img src="/test-assets/shared/fireworks.jpg" role="none" alt="ignore me" />

Passed Example 4

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This svg element that is ignored by assistive technologies because it has no attribute that would give it an accessible name is purely decorative.

<p>Happy new year!</p>
<svg height="200" xmlns="http://www.w3.org/2000/svg">
	<polygon points="100,10 40,180 190,60 10,60 160,180" fill="yellow" />
</svg>

Passed Example 5

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This canvas element that is ignored by assistive technologies because it has no attribute that would give it an accessible name is purely decorative.

<p>Happy new year!</p>
<canvas id="newyear" width="200" height="200"></canvas>
<script>
	const ctx = document.querySelector('#newyear').getContext('2d')
	ctx.fillStyle = 'yellow'
	ctx.beginPath()
	ctx.moveTo(100, 10)
	ctx.lineTo(40, 180)
	ctx.lineTo(190, 60)
	ctx.lineTo(10, 60)
	ctx.lineTo(160, 180)
	ctx.fill()
</script>

Failed

Failed Example 1

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This img element with an empty ("") alt is not purely decorative.

<img src="/test-assets/shared/w3c-logo.png" alt="" />

Failed Example 2

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This img element which is not included in the accessibility tree because aria-hidden is set to true is not purely decorative.

<img src="/test-assets/shared/w3c-logo.png" aria-hidden="true" alt="W3C logo" />

Failed Example 3

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This img element which is not included in the accessibility tree because it has an explicit semantic role of none is not purely decorative.

<img src="/test-assets/shared/w3c-logo.png" role="none" alt="W3C logo" />

Failed Example 4

Open in a new tab

This svg element which has a semantic role of graphics-document and an empty ("") accessible name is not purely decorative.

<p>Best W3C logo:</p>
<svg viewBox="0 0 512 512">
	<path
		d="M108.4 0h23v22.8h21.2V0h23v69h-23V46h-21v23h-23.2M206 23h-20.3V0h63.7v23H229v46h-23M259.5 0h24.1l14.8 24.3L313.2 0h24.1v69h-23V34.8l-16.1 24.8l-16.1-24.8v34.2h-22.6M348.7 0h23v46.2h32.6V69h-55.6"
	/>
	<path fill="#e44d26" d="M107.6 471l-33-370.4h362.8l-33 370.2L255.7 512" />
	<path fill="#f16529" d="M256 480.5V131H404.3L376 447" />
	<path
		fill="#ebebeb"
		d="M142 176.3h114v45.4h-64.2l4.2 46.5h60v45.3H154.4M156.4 336.3H202l3.2 36.3 50.8 13.6v47.4l-93.2-26"
	/>
	<path fill="#fff" d="M369.6 176.3H255.8v45.4h109.6M361.3 268.2H255.8v45.4h56l-5.3 59-50.7 13.6v47.2l93-25.8" />
</svg>

Failed Example 5

Open in a new tab

This canvas element which has no semantic role and an empty ("") accessible name is not purely decorative.

<canvas id="w3c" width="200" height="60"></canvas>
<script>
	const ctx = document.querySelector('#w3c').getContext('2d')
	ctx.font = '30px Arial'
	ctx.fillText('ACT Rules!', 20, 40)
</script>

Inapplicable

Inapplicable Example 1

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This img element is included in the accessibility tree because the alt attribute is not empty ("").

<img src="/test-assets/shared/w3c-logo.png" alt="W3C" />

Inapplicable Example 2

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This img element is neither visible nor included in the accessibility tree.

<img src="/test-assets/shared/w3c-logo.png" style="display:none" alt="" />

Inapplicable Example 3

Open in a new tab

This img element is not visible because it is positioned off screen.

<style>
	img {
		position: absolute;
		top: -9999em;
	}
</style>
<img src="/test-assets/shared/fireworks.jpg" alt="" />

Inapplicable Example 4

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This svg element is ignored because it is a child of a link that provides its accessible name.

<a href="https://example.org" aria-label="SVG star">
	<svg height="200" xmlns="http://www.w3.org/2000/svg">
		<polygon points="100,10 40,180 190,60 10,60 160,180" fill="yellow" />
	</svg>
</a>

Inapplicable Example 5

Open in a new tab

This svg element has a semantic role of img and an accessible name from its aria-label attribute.

<svg viewBox="0 0 512 512" role="img" aria-label="HTML 5 logo">
	<path
		d="M108.4 0h23v22.8h21.2V0h23v69h-23V46h-21v23h-23.2M206 23h-20.3V0h63.7v23H229v46h-23M259.5 0h24.1l14.8 24.3L313.2 0h24.1v69h-23V34.8l-16.1 24.8l-16.1-24.8v34.2h-22.6M348.7 0h23v46.2h32.6V69h-55.6"
	/>
	<path fill="#e44d26" d="M107.6 471l-33-370.4h362.8l-33 370.2L255.7 512" />
	<path fill="#f16529" d="M256 480.5V131H404.3L376 447" />
	<path
		fill="#ebebeb"
		d="M142 176.3h114v45.4h-64.2l4.2 46.5h60v45.3H154.4M156.4 336.3H202l3.2 36.3 50.8 13.6v47.4l-93.2-26"
	/>
	<path fill="#fff" d="M369.6 176.3H255.8v45.4h109.6M361.3 268.2H255.8v45.4h56l-5.3 59-50.7 13.6v47.2l93-25.8" />
</svg>

Inapplicable Example 6

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This canvas element is not visible because it is completely transparent.

<canvas width="200" height="200"></canvas>

Inapplicable Example 7

Open in a new tab

This canvas element has a semantic role of img and an accessible name from its aria-label attribute.

<canvas id="w3c" width="200" height="60" role="img" aria-label="ACT Rules!"></canvas>
<script>
	const ctx = document.querySelector('#w3c').getContext('2d')
	ctx.font = '30px Arial'
	ctx.fillText('ACT Rules!', 20, 40)
</script>

Inapplicable Example 8

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This img element is visible but included in the accessibility tree.

Note: While it might be better for the PDF icon to be ignored by assistive technologies, because assistive technologies will announce "PDF" twice, the image is not purely decorative. Having assistive technologies ignore it is not required by Success Criterion 1.1.1 Non-text content.

<img src="/test-assets/shared/pdf-icon.png" alt="PDF" /> PDF document

Inapplicable Example 9

Open in a new tab

This is a div element with a background image. Background images must be tested separate from this rule.

<p>Happy new year!</p>
<div
	style="
	width: 260px;
	height: 260px;
	background: url(/test-assets/shared/fireworks.jpg) no-repeat;
"
></div>

Inapplicable Example 10

Open in a new tab

This img element has an src attribute which will cause the image request state to be Broken.

<img src="/test-assets/does-not-exist.png" alt="" />

Glossary

Accessible Name

The accessible name is the programmatically determined name of a user interface element that is included in the accessibility tree.

The accessible name is calculated using the accessible name and description computation.

For native markup languages, such as HTML and SVG, additional information on how to calculate the accessible name can be found in HTML Accessibility API Mappings 1.0, Accessible Name and Description Computation (working draft) and SVG Accessibility API Mappings, Name and Description (working draft).

For more details, see examples of accessible name.

Note: As per the accessible name and description computation, each element always has an accessible name. When no accessible name is provided, the element will nonetheless be assigned an empty ("") one.

Note: As per the accessible name and description computation, accessible names are flat string trimmed of leading and trailing whitespace. Notably, it is not possible for a non-empty accessible name to be composed only of whitespace since these must be trimmed.

Accessibility Support for Accessible Name

  • Because the accessible name and description computation is not clear about which whitespace are considered, browsers behave differently when trimming and flattening the accessible name. For example, some browsers completely trim non-breaking spaces while some keep them in the accessible name.
  • There exists a popular browser which does not perform the same trimming and flattening depending whether the accessible name comes from content, an aria-label attribute, or an alt attribute.
  • There exists a popular browser which assign no accessible name (null) when none is provided, instead of assigned an empty accessible name ("").
  • The accessible name and description computation suggest that if an aria-labelledby attribute refers to an existing but empty element, the computation should stop and return an empty name without defaulting to the next steps. Several user agents and assistive technologies chose to use the next step in the computation in this case.

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.

Accessibility Support for Explicit Semantic Role

Some browsers and assistive technologies treat the tokens of the role attribute as case-sensitive. Unless lowercase letters are used for the value of the role attribute, not all user agents will be able to interpret the tokens correctly. ARIA in HTML (working draft) also specifies that authors must use lowercase letters for the role and aria-* attributes.

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:

  • The 1 second time span is an arbitrary limit which is not included in WCAG. Given that scripts can manage the focus state of elements, testing the focusability of an element consistently would be impractical without a time limit.
  • The tabindex value of an element is the value of the tabindex attribute parsed using the rules for parsing integers. For the tabindex value to be different from null, it needs to be parsed without errors.

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).

Accessibility Support for Implicit Semantic Role

  • Images with an empty alt attribute should have an implicit role of presentation, according to the HTML Accessibility API Mapping (work in progress). However, there are several popular browsers that do not treat images with empty alt attribute as having a role of presentation. Instead, they add the img element to the accessibility tree with a role of either img or graphic.

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.

Marked as decorative

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

  • it has an explicit role of none or presentation; or
  • it is an img element with an alt attribute whose value is the empty string (alt=""), and with no explicit role.

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:

  • 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.

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:

  • has a computed CSS property display of none; or
  • has an aria-hidden attribute set to true

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.

Accessibility Support for Definition of Semantic Role for Semantic Role

  • There exist popular web browsers and assistive technologies which do not correctly implement Presentational Roles Conflict Resolution. These technologies will not include in the accessibility tree elements that should be, according to Specifications. Thus, some elements that should have their semantic role fixed by case Conflict above are instead falling into case Explicit and are hidden for users of assistive technologies.
  • A similar conflict exists for focusable elements with a aria-hidden="true" attribute. The WAI ARIA specification does not explain how to solve it. Some browsers give precedence to the element being focusable (and expose it in the accessibility tree) while some give precedence to the aria-hidden attribute (and hide the element).

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.

Useful Links

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. This section will not be included in the rule when it is published on the W3C website.

No Implementations

Implementation reports are not provided for this rule.

Acknowledgments

Authors

Funding

  • WAI-Tools

Assets

  • W3C
  • Wikimedia
  • Adobe
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