Image has non-empty accessible name

  • Rule Type:atomic
  • Rule Id: 23a2a8
  • Last modified: Sep 08, 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 each image either has a non-empty accessible name or is marked up as decorative.

Applicability

The rule applies to HTML img elements and HTML elements with the semantic role of img, except if the element has a hidden state of "true".

Expectation

Each target element has an accessible name that is not empty (""), or has a semantic role of none or presentation.

Assumptions

There are currently no assumptions.

Accessibility Support

  • There is a known combination of a popular browser and assistive technology that does not by default support title as an accessible name.
  • There are several popular browsers that do not treat images with empty alt attribute as having a role of presentation but instead add the img element to the accessibility tree with a semantic role of either img or graphic.
  • Implementation of Presentational Roles Conflict Resolution varies from one browser or assistive technology to another. Depending on this, some elements can have a semantic role of img and fail this rule with some technology but users of other technologies would not experience any accessibility issue.
  • Images can have their role set to presentation through an empty alt attribute. Presentational Roles Conflict Resolution does not specify what to do if such an image is focusable (it only specifies what to do in case of explicit role="none" or role="presentation"). Some browsers expose these images and some don't. Thus, this rule may fail for technologies that expose these without creating an accessibility issue for users of other technologies.

Background

Test Cases

Passed

Passed Example 1

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This HTML img element has an accessible name because of the alt attribute.

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

Passed Example 2

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This element with a semantic role of img has an accessible name because of the aria-label attribute.

<div
	role="img"
	aria-label="W3C logo"
	style="width:72px; height:48px; background-image: url(/test-assets/shared/w3c-logo.png)"
></div>

Passed Example 3

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This element with a semantic role of img has an accessible name because of an aria-labelledby attribute and an element with matching id.

<div style="display: none" id="img-label">W3C logo</div>
<div
	role="img"
	aria-labelledby="img-label"
	style="width:72px; height:48px; background-image: url(/test-assets/shared/w3c-logo.png)"
></div>

Passed Example 4

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This img element has an accessible name because of a title attribute.

Note: There are assistive technologies that do not support using the title attribute for an accessible name, or in which this feature can be disabled.

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

Passed Example 5

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This img element has an implicit role of presentation because of the empty alt attribute.

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

Passed Example 6

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This img element has an explicit role of presentation because of the value of the role attribute.

<img role="presentation" style="width:72px; height:48px; background-image: url(/test-assets/shared/background.png)" />

Passed Example 7

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This img element has an explicit role of none because of the value of the role attribute.

<img role="none" src="/test-assets/shared/background.png" />

Passed Example 8

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This off screen img element has an implicit role of presentation because of the empty alt attribute.

<div style="margin-left:-9999px;">
	<img alt="" src="/test-assets/shared/background.png" />
</div>

Failed

Failed Example 1

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This img element has an empty accessible name and an implicit role of img because it is missing an alt attribute.

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

Failed Example 2

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This element with role of img has an empty accessible name.

<div role="img" style="width:72px; height:48px; background-image: url(/test-assets/shared/w3c-logo.png)"></div>

Failed Example 3

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This img element inside a div positioned off screen has an empty accessible name and an implicit role of img.

<div style="margin-left:-9999px;"><img src="/test-assets/shared/w3c-logo.png" /></div>

Failed Example 4

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This img element has an empty accessible name because the space in the alt attribute is trimmed off by the accessible name computation. Because of the space, the alt attribute is not empty ("") which gives the element the implicit role of img.

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

Failed Example 5

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This img element has an explicit role of none. However, it is focusable due to the tabindex attribute. Because of this it has a semantic role of img due to Presentational Roles Conflict Resolution. It does not have an accessible name.

<img role="none" tabindex="0" src="/test-assets/shared/w3c-logo.png" />

Inapplicable

Inapplicable Example 1

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This svg element has an implicit role of graphics-document.

<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100">
	<circle cx="50" cy="50" r="40" stroke="green" stroke-width="4" fill="yellow" />
</svg>

Inapplicable Example 2

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This element with a semantic role of img is hidden with aria-hidden set to "true".

<div
	role="img"
	aria-hidden="true"
	style="width:72px; height:48px; background-image: url(/test-assets/shared/w3c-logo.png)"
></div>

Inapplicable Example 3

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This img element is hidden with aria-hidden set to "true".

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

Inapplicable Example 4

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This img element is hidden because its parent has display: none.

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

Inapplicable Example 5

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This img element is hidden with visibility: hidden.

<div style="visibility: hidden">
	<img src="/test-assets/shared/w3c-logo.png" />
</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.

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.

Hidden State

An HTML element's hidden state is "true" if at least one of the following is true for itself or any of its ancestors in the flat tree:

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

In any other case, the element's hidden state is "false".

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. 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.

Marked as decorative

An element is marked as decorative if one 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 their hidden state is true. This is different from marking the element as decorative and does not convey the same intention. Notably, the hidden state of an element 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.

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 its hidden state is false, 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.

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).

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.

ToolConsistencyCompleteReport
AlfaconsistentYesView Report
axe-coreconsistentYesView Report
QualWebconsistentYesView Report
SortSiteconsistentYesView Report

Acknowledgments

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