Proposed 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
.
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 theheaders
attribute, the rule may fail on issues that are not accessibility concerns. For example, ifheaders
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 sametable
. If the browser computes an adequate fallback header for cells that have theheaders
attribute value that does not correspond to theid
of any one cell in the sametable
, 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).
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
- Any
H43: Using id and headers attributes to associate data cells with header cells in data tables
- Learn more about technique H43
- Not required for 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
- Any
Input Aspects
The following aspects are required in using this rule.
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:
- 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 eitherImage Button
(the state) orimage
(the keyword mapping to it), both formulations having the same meaning; similarly, “an input element with atype
attribute value ofText
” 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 andfalse
otherwise. Thus<button disabled>
,<button disabled="disabled">
and<button disabled="">
all have adisabled
attribute value oftrue
. - 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
ofnone
; or - has an
aria-hidden
attribute set totrue
Note: Contrarily to the other conditions, the visibility
CSS property may be reverted by descendants.
Note: The HTML standard suggests rendering elements with the hidden
attribute with a CSS rule that applies the value none
to the CSS property display
of the element. Although the suggestion is not normative, known user agents render it according to the suggestion (unless the content specifies another CSS rule that sets the value of the display
property). If a user agent does not follow the suggestion, this definition may produce incorrect results for this user agent.
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.
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.