Table header cell has assigned data cells

  • Rule Type:atomic
  • Rule Id: d0f69e
  • Last modified: Sep 23, 2020
  • 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.

Description

This rule checks that each table header has assigned data cells in a table element.

Applicability

The rule applies to any HTML element with the semantic role of rowheader or columnheader for which all of the following is true:

Expectation

Each target element is assigned to at least one element with a semantic role of cell or gridcell.

Assumptions

This rule assumes that table header cells have a relationship conveyed through presentation with other cells within the same table. This excludes edge cases such as a table definition where there is only one header cell, or a table definition where there are multiple headers and no other cells. In such scenarios the rule fails, but success criterion 1.3.1 Info and Relationships could still be satisfied.

Accessibility Support

  • Table markup and header cell association is not well supported by some popular assistive technologies. Passing this rule can still cause issues for users of those assistive technologies.
  • Implementation of Presentational Roles Conflict Resolution varies from one browser or assistive technology to another. Depending on this, some elements can have one of the applicable semantic roles and fail this rule with some technology but users of other technologies would not experience any accessibility issue.

Background

Test Cases

Passed

Passed Example 1

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This th element has an assigned td element.

<table>
	<tr>
		<th>Time</th>
	</tr>
	<tr>
		<td>05:41</td>
	</tr>
</table>

Passed Example 2

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Each of the 2 span elements with role of columnheader has assigned span elements with a role of cell.

<div role="table">
	<div role="rowgroup">
		<div role="row">
			<span role="columnheader">Month</span>
			<span role="columnheader">Top Temperature</span>
		</div>
	</div>
	<div role="rowgroup">
		<div role="row">
			<span role="cell">July</span>
			<span role="cell">40 C</span>
		</div>
		<div role="row">
			<span role="cell">August</span>
			<span role="cell">45 C</span>
		</div>
	</div>
</div>

Passed Example 3

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Each of the 2 th elements has an assigned td element because this td element spans 2 columns.

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

Passed Example 4

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Each of the 4 th elements has an assigned td element, within the same table element having a semantic role of grid.

<table role="grid">
	<thead>
		<tr role="row">
			<td></td>
			<th scope="col" role="columnheader">Breakfast</th>
			<th scope="col" role="columnheader">Lunch</th>
			<th scope="col" role="columnheader">Dinner</th>
		</tr>
	</thead>
	<tbody>
		<tr role="row">
			<th scope="row" role="rowheader">Day 1</th>
			<td>8:00</td>
			<td>13:00</td>
			<td>18:00</td>
		</tr>
	</tbody>
</table>

Passed Example 5

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Each of the 2 th elements has an assigned td element because the headers attribute assigns the th with id equal to "col2" to the td element.

<table>
	<tr>
		<th id="col1">Cities</th>
		<th id="col2">Count</th>
	</tr>
	<tr>
		<td>Paris</td>
	</tr>
	<tr>
		<td headers="col2">1</td>
	</tr>
</table>

Failed

Failed Example 1

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The th element with text "Value" does not have an assigned cell within the same table element.

<table>
	<thead>
		<tr>
			<th>Rate</th>
			<th>Value</th>
		</tr>
	</thead>
	<tbody>
		<tr>
			<td>15%</td>
		</tr>
	</tbody>
</table>

Failed Example 2

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This th element with id equal to "col2" does not have an assigned cell within the same table element because the headers attribute removes the cell association from its column.

<table>
	<tr>
		<th id="col1">Country</th>
		<th id="col2">Starting with a Z</th>
	</tr>
	<tr>
		<td>Zambia</td>
		<td headers="col1">Zimbabwe</td>
	</tr>
</table>

Failed Example 3

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This div with role of columnheader and text equal to "Occupant" does not have an assigned cell within the same table element.

<div role="grid">
	<div role="row">
		<div role="columnheader">Room</div>
		<div role="columnheader">Occupant</div>
	</div>
	<div role="row">
		<div role="gridcell">1A</div>
	</div>
	<div role="row">
		<div role="gridcell">2A</div>
	</div>
</div>

Inapplicable

Inapplicable Example 1

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There are no elements with a semantic role of header within the table element.

<table>
	<tr>
		<td>12:00</td>
	</tr>
</table>

Inapplicable Example 2

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There are no elements with a semantic role of header within the table element.

<table></table>

Inapplicable Example 3

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This th element has an explicit role of cell and there are no more elements with a semantic role of header within the table element.

<table>
	<tr>
		<th role="cell">Column A</th>
	</tr>
	<tr>
		<td>Cell A</td>
	</tr>
</table>

Inapplicable Example 4

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This th element is neither visible nor included in the accessibility tree and there are no more elements with a semantic role of header within the table element.

<table>
	<tr>
		<th style="display: none;">Organization</th>
	</tr>
	<tr>
		<td>W3C</td>
	</tr>
</table>

Inapplicable Example 5

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This th element is not included in the accessibility tree and there are no more elements with a semantic role of header within the table element.

<table>
	<tr>
		<th aria-hidden="true">Organization</th>
	</tr>
	<tr>
		<td>W3C</td>
	</tr>
</table>

Inapplicable Example 6

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This th element is not a descendant in the flat tree of an element with a semantic role of either table or grid.

<div>
	<tr>
		<th>Column A</th>
	</tr>
</div>

Inapplicable Example 7

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This th element is part of a table which is not included in the accessibility tree.

<table role="presentation">
	<tr>
		<th>Time</th>
	</tr>
	<tr>
		<td>12:00</td>
	</tr>
</table>

Glossary

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).

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
QualWebconsistentYesView Report
SortSiteconsistentYesView Report
Alfapartially-consistentYesView Report
axe-corepartially-consistentYesView Report

Acknowledgments

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