id attribute value is unique

  • Rule Type:atomic
  • Rule Id: 3ea0c8
  • Last modified: Sep 28, 2020
  • Accessibility Requirements Mapping:
    • 4.1.1 Parsing (Level A)
      • Learn More about 4.1.1 Parsing
      • 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.
    • H93: Ensuring that id attributes are unique on a Web page
      • Learn More about technique H93
      • Not required to conformance to any W3C accessibility recommendation.
      • Outcome mapping:
        • Any failed outcomes: technique is not satisfied.
        • All passed outcomes: technique is satisfied.
        • An inapplicable outcome: technique is satisfied.
  • Input Aspects:

Description

This rule checks that all id attribute values on a single page are unique.

Applicability

Any id attribute whose value is not an empty string (""), specified on a HTML or SVG element.

Note: Elements that are neither included in the accessibility tree nor visible are still considered for this rule.

Expectation

The value of the attribute is unique across all other id attributes specified on HTML or SVG elements that exist within the same document tree or shadow tree as the element on which the applicable id attribute is specified.

Assumptions

There are currently no assumptions.

Accessibility Support

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

Background

Test Cases

Passed

Passed Example 1

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There is only one id attribute within the document context.

<div id="my-div">This is my first element</div>

Passed Example 2

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All id attributes are unique within the document context.

<div id="my-div1">This is my first element</div>
<div id="my-div2">This is my second element</div>
<svg id="my-div3">This is my third element</svg>

Passed Example 3

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Two of the id attributes are the same (my-elt), but they are in different trees (the first one in the document tree and the second in the shadow tree).

<div id="my-elt"></div>
<div id="host"></div>
<script>
	var host = document.getElementById('host')
	var shadow = host.attachShadow({ mode: 'open' })
	shadow.innerHTML = '<b id="my-elt"></b>'
</script>

Passed Example 4

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Both id attributes are the same (my-elt), but they are in different document trees because the iframe is creating a new one.

<div id="my-elt"></div>
<iframe title="Empty frame" srcdoc="<span id='my-elt'></span>"></iframe>

Failed

Failed Example 1

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The id attribute label is not unique among all id attributes in the document, resulting in a wrong programmatic label on the input field.

<div id="label">Name</div>
<div id="label">City</div>

<input aria-labelledby="label" type="text" name="city" />

Failed Example 2

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The id attribute label is not unique among all id attributes in the document, resulting in a wrong programmatic label on the input field.

<div id="label">Name</div>
<svg id="label">
	<text x="0" y="15">City</text>
</svg>

<input aria-labelledby="label" type="text" name="city" />

Failed Example 3

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The id attribute label is not unique among all id attributes in the document, resulting in a wrong programmatic label on the input field. This rule still considers elements that are neither included in the accessibility tree nor visible.

<span id="label" style="display: none;">Name</span>
<span id="label">City</span>

<input aria-labelledby="label" type="text" name="city" />

Inapplicable

Inapplicable Example 1

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There is no id attribute in this document.

<div>This is my first element</div>

Inapplicable Example 2

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The xml:id attribute is not considered by this rule.

<div xml:id="my-div">This is my first element</div>

Inapplicable Example 3

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These id attributes have an empty value.

<span id="">Hello</span> <span id="">world!</span>

Glossary

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.

ToolConsistencyCompleteReport
AlfaconsistentYesView Report
axe-coreconsistentYesView Report
QualWebconsistentYesView Report
SortSiteconsistentYesView Report

Acknowledgments

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