Headers attribute specified on a cell refers to cells in the same table element

Rule Type:atomic
Rule Id: a25f45
Last modified: Jun 23, 2022
Accessibility Requirements Mapping:
- 1.3.1 Info and Relationships (Level A)
  - Learn More about 1.3.1 Info and Relationships
  - 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.
- H43: Using id and headers attributes to associate data cells with header cells in data tables
  - Learn More about technique H43
  - 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.
Input Aspects:
- DOM Tree
- CSS Styling

Description

This rule checks that the headers attribute on a cell refer to other cells in the same table element.

Applicability

This rule applies to any headers attribute specified on a cell within a table element, where the table element is visible and included in the accessibility tree.

Expectation 1

Each target's attribute value is a set of space separated tokens. Each token is the value of the id attribute of an element, that is a cell of the same table.

Expectation 2

Each target's attribute value is a set of space separated tokens, and none of these tokens is the id of the element on which the test target is specified.

Assumptions

This rule assumes that the headers attribute is only used to identify table headers. If other information is included in the headers attribute, the rule may fail on issues that are not accessibility concerns. For example, if headers is used to include information for scripts, this rule may not be accurate.
This rule assumes that the headers attribute is required to express the relationship between data and table header cells in the same table. If the browser computes an adequate fallback header for cells that have the headers attribute value that does not correspond to the id of any one cell in the same table, success Criterion 1.3.1 Info and Relationships may be satisfied even if this rule failed.
This rule assumes that the id values on the headers attribute are unique.

Accessibility Support

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

Background

Bibliography

Understanding Success Criterion 1.3.1: Info and Relationships
H43: Using id and headers attributes to associate data cells with header cells in data tables
F90: Incorrectly associating table headers and content via the headers and id attributes
headers attribute referencing elements that are non-existent or not in the table are ignored when assigning header cells (step 3, first case, point 2).
headers attribute referencing to the cell itself are ignored when assigning header cells (step 3, first case, point 2).

Test Cases

Passed

Passed Example 1

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The headers attribute on the data cells refers to a th element within the same table.

<table>
	<thead>
		<tr>
			<th id="header1">Projects</th>
			<th id="header2">Objective</th>
		</tr>
	</thead>
	<tbody>
		<tr>
			<td headers="header1">15%</td>
			<td headers="header2">10%</td>
		</tr>
	</tbody>
</table>

Passed Example 2

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The headers attribute on the cell refers to a th element within the same table. Multiple headers are referenced for a cell with colspan of 2.

<table>
	<thead>
		<tr>
			<th id="header1">Projects</th>
			<th id="header2">Exams</th>
		</tr>
	</thead>
	<tbody>
		<tr>
			<td colspan="2" headers="header1 header2">15%</td>
		</tr>
	</tbody>
</table>

Passed Example 3

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The headers attribute on the data cells in the second row refers to a td element with a role of columnheader within the same table.

<table>
	<thead>
		<tr>
			<td role="columnheader" id="header1">Projects</td>
			<td role="columnheader" id="header2">Objective</td>
		</tr>
	</thead>
	<tbody>
		<tr>
			<td headers="header1">15%</td>
			<td headers="header2">10%</td>
		</tr>
	</tbody>
</table>

Passed Example 4

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This table has multiple elements with a role of columnheader. The headers attribute on the cells lists IDs of th elements within the same table.

<table>
	<tr>
		<th colspan="2" id="header1">Projects</th>
		<th colspan="2" id="header2">Exams</th>
	</tr>
	<tr>
		<th id="e1" headers="header1">1</th>
		<th id="e2" headers="header1">2</th>
		<th id="p1" headers="header2">1</th>
		<th id="p2" headers="header2">2</th>
	</tr>
	<tr>
		<td colspan="2" headers="header1 e1 e2">15%</td>
		<td headers="header2 p1">15%</td>
		<td headers="header2 p2">45%</td>
	</tr>
</table>

Passed Example 5

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The headers attribute on the second data cell in each row refers to a th element with a role of rowheader within the same table.

<table>
	<tbody>
		<tr>
			<th role="rowheader" id="headerAge">Age</th>
			<td headers="headerAge">65</td>
		</tr>
		<tr>
			<th role="rowheader" id="headerObjective">Objective</th>
			<td headers="headerObjective">40%</td>
		</tr>
	</tbody>
</table>

Passed Example 6

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The headers attribute on the last two th elements refers to another th element within the same table. Here the column header has a span of two columns.

<table>
	<tr>
		<th id="name" colspan="2">Name</th>
	</tr>
	<tr>
		<th headers="name">Firstname</th>
		<th headers="name">Lastname</th>
	</tr>
</table>

Passed Example 7

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The headers attribute on the cells refers to th elements which are row scoped & within the same table.

<table>
	<tr>
		<th id="projects1" scope="row">Projects</th>
		<th id="progress1" scope="row">Progress</th>
	</tr>
	<tr>
		<td headers="projects1">My Project</td>
		<td headers="progress1">15%</td>
	</tr>
</table>

Passed Example 8

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The headers attribute on the cell refers to th element which is not the same column as the cell.

<table>
	<tr>
		<td></td>
		<th id="projects2">Projects</th>
	</tr>
	<tr>
		<td headers="projects2">15%</td>
		<td></td>
	</tr>
</table>

Failed

Failed Example 1

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The td elements have a headers attribute referring to an ID that does not exist within the same table. Here the referenced ID is incorrect.

<table>
	<tr>
		<th id="headerOfColumn1">Projects</th>
		<th id="headerOfColumn2">Objective</th>
	</tr>
	<tr>
		<td headers="headOfColumn1">15%</td>
		<td headers="headOfColumn2">10%</td>
	</tr>
</table>

Failed Example 2

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The td elements have a headers attribute referring to an ID that exist in a separate table.

<table>
	<tr>
		<th id="headOfColumn1">Projects</th>
		<th id="headOfColumn2">Objective</th>
	</tr>
</table>

<table>
	<tr>
		<td headers="headOfColumn1">15%</td>
		<td headers="headOfColumn2">10%</td>
	</tr>
</table>

Failed Example 3

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The td element has a headers attribute referring to its own ID.

<table>
	<tr>
		<th>Event Type</th>
	</tr>
	<tr>
		<td id="headerBday" headers="headerBday">
			Birthday
		</td>
	</tr>
</table>

Failed Example 4

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The headers attribute on the data cells in the second row refers to an element inside the same table which does not have a role of rowheader or columnheader.

<table>
	<tr>
		<td>
			<span id="headerProject">Projects</span>
		</td>
		<td>
			<span id="headerObjective">Objective</span>
		</td>
	</tr>
	<tr>
		<td headers="headerProject">
			15%
		</td>
		<td headers="headerObjective">
			10%
		</td>
	</tr>
</table>

Inapplicable

Inapplicable Example 1

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There is no headers attribute.

<table>
	<tr>
		<th scope="col">Projects</th>
		<th scope="col">Exams</th>
	</tr>
	<tr>
		<td>15%</td>
		<td>45%</td>
	</tr>
</table>

Inapplicable Example 2

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The table has a role="presentation" and thus is not included in the accessibility tree.

<table role="presentation">
	<tr>
		<td id="header1">Project Status</td>
		<td id="header2">Objective</td>
	</tr>
	<tr>
		<td headers="header1">15%</td>
		<td headers="header2">10%</td>
	</tr>
</table>

Inapplicable Example 3

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The table is not visible in page.

<html>
	<style>
		.notInPage {
			position: absolute;
			left: -9999px;
			top: -9999px;
		}
	</style>
	<table class="notInPage">
		<tr>
			<th id="header1">Project Status</th>
			<th id="header2">Objective</th>
		</tr>
		<tr>
			<td headers="header1">15%</td>
			<td headers="header2">10%</td>
		</tr>
	</table>
</html>

Inapplicable Example 4

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The rule applies only to headers attribute within a table element.

<div role="table">
	<div role="row">
		<div role="columnheader" id="header1">Projects</div>
		<div role="columnheader" id="header2">Exams</div>
	</div>
	<div role="row">
		<div role="cell" headers="header2">15%</div>
		<div role="cell" headers="header1">15%</div>
	</div>
</div>

Inapplicable Example 5

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The table is not included in the accessibility tree.

<table style="display:none;">
	<tr>
		<td id="header1">Project Status</td>
		<td id="header2">Objective</td>
	</tr>
	<tr>
		<td headers="header1">15%</td>
		<td headers="header2">10%</td>
	</tr>
</table>

The attribute value of a content attribute set on an HTML element is the value that the attribute gets after being parsed and computed according to specifications. It may differ from the value that is actually written in the HTML code due to trimming whitespace or non-digits characters, default values, or case-insensitivity.

Some notable case of attribute value, among others:

For enumerated attributes, the attribute value is either the state of the attribute, or the keyword that maps to it; even for the default states. Thus <input type="image" /> has an attribute value of either Image Button (the state) or image (the keyword mapping to it), both formulations having the same meaning; similarly, "an input element with a type attribute value of Text" can be either <input type="text" />, <input /> (missing value default), or <input type="invalid" /> (invalid value default).
For boolean attributes, the attribute value is true when the attribute is present and false otherwise. Thus <button disabled>, <button disabled="disabled"> and <button disabled=""> all have a disabled attribute value of true.
For attributes whose value is used in a case-insensitive context, the attribute value is the lowercase version of the value written in the HTML code.
For attributes that accept numbers, the attribute value is the result of parsing the value written in the HTML code according to the rules for parsing this kind of number.
For attributes that accept sets of tokens, whether space separated or comma separated, the attribute value is the set of tokens obtained after parsing the set and, depending on the case, converting its items to lowercase (if the set is used in a case-insensitive context).
For aria-* attributes, the attribute value is computed as indicated in the WAI-ARIA specification and the HTML Accessibility API Mappings.

This list is not exhaustive, and only serves as an illustration for some of the most common cases.

The attribute value of an IDL attribute is the value returned on getting it. Note that when an IDL attribute reflects a content attribute, they have the same attribute value.

Focusable

An element is focusable if one or both of the following are true:

the element is part of sequential focus navigation; or
the element has a tabindex value that is not null.

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.

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.

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.

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.

Tool	Consistency	Complete	Report
Alfa	consistent	Yes	View Report
Equal Access Accessibility Checker	consistent	Yes	View Report
QualWeb	consistent	Yes	View Report
SortSite	consistent	No	View Report
axe-core	partially-consistent	Yes	View Report

Acknowledgments

Authors

Funding

WAI-Tools

Table of Contents

Glossary
Useful Links
Implementations
Acknowledgments

Description

Applicability

Expectation 1

Expectation 2

Assumptions

Accessibility Support

Background

Bibliography

Test Cases

Passed

Passed Example 1

Passed Example 2

Passed Example 3

Passed Example 4

Passed Example 5

Passed Example 6

Passed Example 7

Passed Example 8

Failed

Failed Example 1

Failed Example 2

Failed Example 3

Failed Example 4

Inapplicable

Inapplicable Example 1

Inapplicable Example 2

Inapplicable Example 3

Inapplicable Example 4

Inapplicable Example 5

Glossary

Attribute value

Focusable

Included in the accessibility tree

Outcome

Programmatically Hidden

Visible

Useful Links

Implementations

Acknowledgments

Authors

Funding