Image accessible name is descriptive

  • Rule Type:atomic
  • Rule Id: qt1vmo
  • Last modified: Jul 17, 2020
  • 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.
    • G94: Providing short text alternative for non-text content that serves the same purpose and presents the same information as the non-text content
      • Learn More about technique G94
      • Not required to conformance to any W3C accessibility recommendation.
      • Outcome mapping:
        • Any failed outcomes: technique is not satisfied.
        • All passed outcomes: technique needs further testing.
        • An inapplicable outcome: technique needs further testing.
    • G95: Providing short text alternatives that provide a brief description of the non-text content
      • Learn More about technique G95
      • Not required to conformance to any W3C accessibility recommendation.
      • Outcome mapping:
        • Any failed outcomes: technique is not satisfied.
        • All passed outcomes: technique needs further testing.
        • An inapplicable outcome: technique needs further testing.

Description

This rule checks that the accessible names of images serves an equivalent purpose to the image.

Applicability

Any img, canvas or svg element that is visible and has a non-empty accessible name, except if one of the following is true:

Expectation

Each test target has an accessible name that serves an equivalent purpose to the non-text content of that test target.

Assumptions

This rule assumes that the language of the accessible name of each test target can be correctly determined (either programmatically or by analyzing the content).

Accessibility Support

There are no major accessibility support issues known for this rule.

Background

Test Cases

Passed

Passed Example 1

Open in a new tab

This img element has an alt attribute that describes the image.

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

Passed Example 2

Open in a new tab

This svg element has an aria-label attribute that describes the image.

<html lang="en">
	<svg viewBox="0 0 512 512" aria-label="HTML 5">
		<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>
</html>

Passed Example 3

Open in a new tab

This canvas element has an aria-label attribute that describes the image.

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

Failed

Failed Example 1

Open in a new tab

This img element has an alt attribute that incorrectly describes the image.

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

Failed Example 2

Open in a new tab

This svg element has an aria-label attribute that incorrectly describes the image.

<html lang="en">
	<svg viewBox="0 0 512 512" aria-label="W3C">
		<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>
</html>

Failed Example 3

Open in a new tab

This canvas element has an aria-label attribute that incorrectly describes the image.

<html lang="en">
	<canvas id="act" width="200" height="60" aria-label="HTML 5"></canvas>
	<script>
		const ctx = document.querySelector('#act').getContext('2d')
		ctx.font = '30px Arial'
		ctx.fillText('ACT Rules!', 20, 40)
	</script>
</html>

Inapplicable

Inapplicable Example 1

Open in a new tab

This img element has an empty ("") accessible name. The image is described by the adjacent text.

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

Inapplicable Example 2

Open in a new tab

This decorative img element has an empty ("") accessible name because it has no attributes or content to provide an accessible name.

<html lang="en">
	<img src="/test-assets/shared/fireworks.jpg" role="presentation" />
</html>

Inapplicable Example 3

Open in a new tab

This svg element has an empty ("") accessible name because it has no attributes or content to provide an accessible name.

<html lang="en">
	<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>
</html>

Inapplicable Example 4

Open in a new tab

This canvas element has an empty ("") accessible name because it has no attributes or content to provide an accessible name.

<html lang="en">
	<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>
</html>

Inapplicable Example 5

Open in a new tab

This img element is not visible.

<html lang="en">
	<img src="/test-assets/shared/w3c-logo.png" alt="W3C" style="display:none" />
</html>

Inapplicable Example 6

Open in a new tab

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

<html lang="en">
	<canvas width="200" height="200"></canvas>
</html>

Inapplicable Example 7

Open in a new tab

This img element has no accessible name because it is not included in the accessibility tree.

<html lang="en">
	<img aria-hidden="true" src="/test-assets/shared/fireworks.jpg" alt="fireworks" />
</html>

Inapplicable Example 8

Open in a new tab

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

<a href="https://w3.org" aria-label="W3C Website">
	<svg height="200" xmlns="http://www.w3.org/2000/svg" aria-label="star">
		<polygon points="100,10 40,180 190,60 10,60 160,180" fill="yellow" />
	</svg>
</a>

Inapplicable Example 9

Open in a new tab

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

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

Inapplicable Example 10

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>

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.

Included in the accessibility tree

Elements included in the accessibility tree of platform specific accessibility APIs. Elements in the accessibility tree are exposed to assistive technologies, allowing users to interact with the elements in a way that meet 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.

Note: Users of assistive technologies might still be able to interact with elements that are not included in the accessibility tree. An example of this is a focusable element with an aria-hidden attribute with a value of true. Such an element could still be interacted using sequential keyboard navigation regardless of the assistive technologies used, even though the element would not be included in the accessibility tree.

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.

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

Assets

  • W3C; HTML and W3C logo
  • Wikimedia; Fireworks image
  • Adobe; PDF logo
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