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Proposed ARIA required ID references exist

Description

This rule checks that every ID reference required by WAI-ARIA exists

Applicability

This rule applies to any aria-controls attribute defined on an [HTML element][namespaced element] for which one of the following is true:

Expectation

Each test target’s attribute value is a space-separated list of one or more IDs. At least one of those IDs must match an id attribute value in the same shadow tree or, if not within a shadow tree, within the same document.

Background

This rule is written specifically for aria-controls, because it is the only ID Reference List property that is required by WAI-ARIA. The aria-controls property is only required by the scrollbar role and by an expanded combobox. There are no ID Reference properties that are required by WAI-ARIA for any role.

Assumptions

There are no assumptions.

Accessibility Support

Some user agents treat the value of aria-* attribute as case-sensitive (even when these are not IDs) while some treat them as case-insensitive.

Bibliography

Accessibility Requirements Mapping

Secondary Requirements

This rule is related to the following accessibility requirements, but was not designed to test this requirements directly. These secondary requirements can either be stricter than the rule requires, or may be satisfied in ways not tested by the rule:

Input Aspects

The following aspects are required in using this rule.

Test Cases

Passed

Passed Example 1

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The aria-controls attribute value of this scrollbar matches the id of the main element in the same document.

<main id="content">Lorem ipsum...</main>
<div
	role="scrollbar"
	aria-controls="content"
	aria-orientation="vertical"
	aria-valuemax="100"
	aria-valuemin="0"
	aria-valuenow="25"
></div>

Passed Example 2

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The aria-controls attribute value of this expanded combobox matches the id of the ul element in the same document.

<label for="tag_combo">Tag</label>
<input
	type="text"
	id="tag_combo"
	role="combobox"
	aria-expanded="true"
	aria-controls="popup_listbox"
	aria-activedescendant="selected_option"
/>
<ul role="listbox" id="popup_listbox">
	<li role="option">Zebra</li>
	<li role="option" id="selected_option">Zoom</li>
</ul>

Passed Example 3

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The aria-controls attribute value of this scrollbar has two IDs. The content-2 ID matches the id of the main element in the same document.

<main id="content-2">Lorem ipsum...</main>
<div
	role="scrollbar"
	aria-controls="content-1 content-2"
	aria-orientation="vertical"
	aria-valuemax="100"
	aria-valuemin="0"
	aria-valuenow="25"
></div>

Failed

Failed Example 1

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The aria-controls attribute of this expanded combobox references an ID of popup_listbox which does not exist in the document.

<label>
	Tag
	<input role="combobox" aria-expanded="true" aria-controls="popup_listbox" />
</label>

Failed Example 2

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The aria-controls attribute of this scrollbar references IDs of content-1 and content-2. Neither of these IDs exist in the document.

<main>Lorem ipsum...</main>
<div
	role="scrollbar"
	aria-controls="content-1 content-2"
	aria-orientation="vertical"
	aria-valuemax="100"
	aria-valuemin="0"
	aria-valuenow="25"
></div>

Failed Example 3

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The aria-controls attribute of this expanded combobox references a popup_listbox ID. This id exists, but in a different DOM tree as the combobox.

<div id="aria-listbox">
	<label for="tag_combo">Tag</label>
	<input
		type="text"
		id="tag_combo"
		role="combobox"
		aria-expanded="true"
		aria-controls="popup_listbox"
		aria-activedescendant="selected_option"
	/>
</div>
<script>
	const ariaListbox = document.querySelector('#aria-listbox')
	const shadowRoot = ariaListbox.attachShadow({ mode: 'open' })
	shadowRoot.innerHTML = `
		<slot></slot>
		<ul role="listbox" id="popup_listbox">
			<li role="option">Zebra</li>
			<li role="option" id="selected_option">Zoom</li>
		</ul>
	`
</script>

Inapplicable

Inapplicable Example 1

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The aria-controls attribute is defined on a combobox which does not have an aria-expanded attribute value of true.

<label for="tag_combo">Tag</label>
<input type="text" id="tag_combo" role="combobox" aria-expanded="false" aria-controls="popup_listbox" />

Inapplicable Example 2

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This aria-controls attribute is not defined on a semantic scrollbar nor combobox.

<button aria-controls="my-modal">Open the modal</button>

Inapplicable Example 3

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There is no aria-controls attribute.

<button>Open the modal</button>

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.

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.

Focusable

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

Exception: Elements that lose focus and do not regain 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:

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).

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:

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.

Outcome

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 five following types:

Note: A rule has one passed or failed outcome for every test target. When a tester evaluates a test target it can also be reported as cantTell if the rule cannot be tested in its entirety. For example, when applicability was automated, but the expectations have to be evaluated manually.

When there are no test targets the rule has one inapplicable outcome. If the tester is unable to determine whether there are test targets there will be one cantTell outcome. And when no evaluation has occurred the test target has one untested outcome. This means that each test subject always has one or more outcomes.

Outcomes used in ACT Rules can be expressed using the outcome property of the [EARL10-Schema][].

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:

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.

WAI-ARIA specifications

The WAI ARIA Specifications group both the WAI ARIA W3C Recommendation and ARIA modules, namely:

Note: depending on the type of content being evaluated, part of the specifications might be irrelevant and should be ignored.

Rule Versions

This is the first version of this ACT rule.

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 Type Consistency Report
Alfa (fully automated) 0.80.0 Automated tool Consistent Alfa (fully automated) Report
Alfa (semi-automated) 0.80.0 Semi-automated tool Consistent Alfa (semi-automated) Report
QualWeb 3.0.0 Automated tool Consistent QualWeb Report
SortSite 6.45 Automated tool Consistent SortSite Report
Total Validator 17.4.0 Linter Consistent Total Validator Report
Total Validator (+Browser) 17.4.0 Automated tool Consistent Total Validator (+Browser) Report
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