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Audit td-headers-attr

Ensure that each cell in a table that uses the headers attribute refers only to other <th> elements in that table

Impact:

Serious

WCAG-Konformität:

A
WCAG 1.3.1

Issue types:

failure, needs review

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

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 all of the following is true for the table element:

The table is visible; and
The table is included in the accessibility tree; and
The table has a semantic role of table, grid or treegrid.

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.

Background

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 accessibility support issues known.

Bibliography

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

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 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

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

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>

Inapplicable Example 6

This table doesn't have a role of table, grid or treegrid.

<table role="region">
	<td id="self" headers="self">World</td>
</table>

Autoren: Audrey Maniez, Jey Nandakumar

Finanzierung: WAI-Tools