ACT-Rules Community

Table header cell has assigned cells

  • Rule Type:atomic
  • Rule Id: d0f69e
  • Last modified: Jan 11, 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.
  • Input Aspects:

Description

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

Applicability

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

Expectation

Each target element is assigned to at least one element with an inheriting semantic cell.

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

The roles inheriting from cell are columnheader, gridcell, and rowheader.

Bibliography

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>

Passed Example 6

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Each of the 5 th elements in this table has assigned cells, whether data or header.

<table>
	<caption>
		Opening hours
	</caption>
	<tr>
		<th>Day</th>
		<th>Morning</th>
		<th>Afternoon</th>
	</tr>
	<tr>
		<th>Mon-Fri</th>
		<td>8-12</td>
		<td>14-17</td>
	</tr>
	<tr>
		<th>Sat-Sun</th>
		<td>10-14</td>
		<td>Closed</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 a semantic 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.

Focusable

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

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.

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 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.

Marked as decorative

An element is marked as decorative if one or more 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 they are programmatically hidden. This is different from marking the element as decorative and does not convey the same intention. Notably, being programmatically hidden 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.

Namespaced Element

An element with a specific namespaceURI value from HTML namespaces. For example an "SVG element" is any element with the "SVG namespace", which is http://www.w3.org/2000/svg.

Namespaced elements are not limited to elements described in a specification. They also include custom elements. Elements such as a and title have a different namespace depending on where they are used. For example a title in an HTML page usually has the HTML namespace. When used in an svg element, a title element has the SVG namespace instead.

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.

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 it is not programmatically hidden, 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.

This definition can be used in expressions such as "semantic button" meaning any element with a semantic role of button.

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

Authors

Funding

  • WAI-Tools
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