Proposed Test Rule: headers attribute specified on a cell refers to cells in the same table element

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.

Note: 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).

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.

Note: headers attribute referencing to the cell itself are ignored when assigning header cells (step 3, first case, point 2).

Assumptions

Accessibility Support

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

Background

Test Cases

Passed

Passed Example 1

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

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

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

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

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

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

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

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

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

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 3

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

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

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

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

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

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>

Glossary

Attribute value

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:

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

Elements that can become the target of keyboard input as described in the HTML specification of focusable and can be focused.

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. [examples of included in the accessibility tree]: https://act-rules.github.io/pages/examples/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:

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.

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.

Implementation Consistency Complete Report
Alfa Consistent Yes View Report
Axe-core Consistent Yes View Report
QualWeb Consistent Yes View Report
SortSite Consistent Yes View Report

Changelog

This is the first version of this ACT rule.

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This is an unpublished draft preview that might include content that is not yet approved. The published website is at w3.org/WAI/.