Proposed Scrollable content can be reached with sequential focus navigation

Description

This rule checks that scrollable elements or their descendants can be reached with sequential focus navigation so that they can be scrolled by keyboard

Applicability

This rule applies to any HTML element that has visible children in the flat tree, and for which at least one of the following is true:

• the element has a horizontal scroll distance greater than the computed left or right padding of the element; or
• the element has a vertical scroll distance greater than the computed top or bottom padding of the element.

Expectation

Each test target is either included in sequential focus navigation or has a descendant in the flat tree that is included in sequential focus navigation.

Assumptions

This rule assumes that all scrollable elements with visible content need to be keyboard accessible. Scrollable elements that do not need to be keyboard accessible, perhaps because their content is purely decorative, the scroll area is whitespace, or because scroll can be controlled in some other keyboard accessible way such as through a button or custom scrollbar, may fail this rule but still satisfy success criterion 2.1.1 Keyboard.

Accessibility Support

Some browsers will automatically make any scrollable element focusable to ensure keyboard accessibility. However, the browser does not include these elements in sequential focus navigation when it has a negative number as a tabindex attribute value.

Some browsers restrict scrolling to the content box of elements; while others allow to scroll the full border box, hence including the element’s padding. This results in some elements being scrollable with a browser but not with another.

Background

To ensure there is some element from which arrow keys can be used to control the scroll position, focus must be on or in a scrollable region. If scripts are used to prevent the keyboard events from reaching the scrollable region, this could still cause a keyboard accessibility issue. This must be tested separately.

This rule only applies to elements who scroll content in the same document. Elements such as iframes that embed other documents may also be scrollable, but for them it is the embedded document that scrolls, not the content in the same document. Such scenarios are tested separately with rules such as Iframe with negative tabindex has no interactive elements.

Bibliography

• Understanding Success Criterion 2.1.1: Keyboard
• G202: Ensuring keyboard control for all functionality

Accessibility Requirements Mapping

• 2.1.1 Keyboard (Level A)

  • Learn more about 2.1.1 Keyboard
  • 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
• 2.1.3 Keyboard (No Exception) (Level AAA)

  • Learn more about 2.1.3 Keyboard (No Exception)
  • Required for conformance to WCAG 2.0 and later on level AAA.
  • 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
• G202: Ensuring keyboard control for all functionality

  • Learn more about technique G202
  • 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

Input Aspects

The following aspects are required in using this rule.

• DOM Tree
• CSS Styling

Test Cases

Passed

Passed Example 1

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This scrollable section element is included in sequential focus navigation because it has a tabindex attribute set to 0.

<section style="height: 100px; width: 500px; overflow: scroll;" tabindex="0">
	<h1>WCAG 2.1 Abstract</h1>
	<p>
		Web Content Accessibility Guidelines (WCAG) 2.1 covers a wide range of recommendations for making Web content more
		accessible. Following these guidelines will make content more accessible to a wider range of people with
		disabilities, including accommodations for blindness and low vision, deafness and hearing loss, limited movement,
		speech disabilities, photosensitivity, and combinations of these, and some accommodation for learning disabilities
		and cognitive limitations; but will not address every user need for people with these disabilities. These guidelines
		address accessibility of web content on desktops, laptops, tablets, and mobile devices. Following these guidelines
		will also often make Web content more usable to users in general.
	</p>
</section>

Passed Example 2

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This scrollable section element contains a link that is included in sequential focus navigation.

<section style="height: 100px; width: 500px; overflow: scroll;">
	<h1>
		<a href="https://www.w3.org/TR/WCAG21/#abstract">
			WCAG 2.1 Abstract
		</a>
	</h1>
	<p>
		Web Content Accessibility Guidelines (WCAG) 2.1 covers a wide range of recommendations for making Web content more
		accessible. Following these guidelines will make content more accessible to a wider range of people with
		disabilities, including accommodations for blindness and low vision, deafness and hearing loss, limited movement,
		speech disabilities, photosensitivity, and combinations of these, and some accommodation for learning disabilities
		and cognitive limitations; but will not address every user need for people with these disabilities. These guidelines
		address accessibility of web content on desktops, laptops, tablets, and mobile devices. Following these guidelines
		will also often make Web content more usable to users in general.
	</p>
</section>

Failed

Failed Example 1

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This vertically scrollable section element is not included in sequential focus navigation, nor does it have any descendants that are.

<section style="height: 100px; width: 500px; overflow-y: scroll">
	<h1>WCAG 2.1 Abstract</h1>
	<p>
		Web Content Accessibility Guidelines (WCAG) 2.1 covers a wide range of recommendations for making Web content more
		accessible. Following these guidelines will make content more accessible to a wider range of people with
		disabilities, including accommodations for blindness and low vision, deafness and hearing loss, limited movement,
		speech disabilities, photosensitivity, and combinations of these, and some accommodation for learning disabilities
		and cognitive limitations; but will not address every user need for people with these disabilities. These guidelines
		address accessibility of web content on desktops, laptops, tablets, and mobile devices. Following these guidelines
		will also often make Web content more usable to users in general.
	</p>
</section>

Failed Example 2

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This horizontally scrollable section element is not included in sequential focus navigation, nor does it have any descendants that are.

<style>
	section {
		height: 100px;
		width: 400px;
		overflow-y: auto;
		white-space: nowrap;
	}
	section > img {
		display: inline-block;
		width: 80px;
	}
</style>
<h1>Our sponsors:</h1>
<section>
	<img src="/test-assets/shared/w3c-logo.png" alt="W3C" />
	<img src="/test-assets/shared/eu-logo.svg" alt="EU" />
	<img src="/test-assets/shared/w3c-logo.png" alt="W3C" />
	<img src="/test-assets/shared/eu-logo.svg" alt="EU" />
	<img src="/test-assets/shared/w3c-logo.png" alt="W3C" />
	<img src="/test-assets/shared/eu-logo.svg" alt="EU" />
	<img src="/test-assets/shared/w3c-logo.png" alt="W3C" />
</section>

Inapplicable

Inapplicable Example 1

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This section element has a computed overflow of visible. Because of this its scroll distance will be 0, regardless of the element’s content.

<section style="height: 95px; width: 500px;">
	<h1>WCAG 2.1 Abstract</h1>
	<p>
		Web Content Accessibility Guidelines (WCAG) 2.1 covers a wide range of recommendations for making Web content more
		accessible. Following these guidelines will make content more accessible to a wider range of people with
		disabilities, including accommodations for blindness and low vision, deafness and hearing loss, limited movement,
		speech disabilities, photosensitivity, and combinations of these, and some accommodation for learning disabilities
		and cognitive limitations; but will not address every user need for people with these disabilities. These guidelines
		address accessibility of web content on desktops, laptops, tablets, and mobile devices. Following these guidelines
		will also often make Web content more usable to users in general.
	</p>
</section>

Inapplicable Example 2

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This section element has a scroll distance of 0 in both directions.

<section style="height: 95px; width: 500px; overflow: auto;">
	<p>
		<a href="https://www.w3.org/TR/WCAG21/#abstract">
			WCAG 2.1 Abstract
		</a>
	</p>
</section>

Inapplicable Example 3

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This section element is not scrollable because it has a computed overflow of hidden.

<h1>
	<a href="https://www.w3.org/TR/WCAG21/#abstract">
		WCAG 2.1 Abstract
	</a>
</h1>
<section style="height: 95px; width: 500px; overflow: hidden;">
	<p>
		Web Content Accessibility Guidelines (WCAG) 2.1 covers a wide range of recommendations for making Web content more
		accessible. Following these guidelines will make content more accessible to a wider range of people with
		disabilities, including accommodations for blindness and low vision, deafness and hearing loss, limited movement,
		speech disabilities, photosensitivity, and combinations of these, and some accommodation for learning disabilities
		and cognitive limitations; but will not address every user need for people with these disabilities. These guidelines
		address accessibility of web content on desktops, laptops, tablets, and mobile devices. Following these guidelines
		will also often make Web content more usable to users in general.
	</p>
</section>

Inapplicable Example 4

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This scrollable section element has no visible content.

<p>This is what a scrollbar looks like:</p>
<section style="height: 20px; width: 500px; overflow-x:scroll;">
	<div style="width: 1000px; height: 1px;"></div>
</section>

Inapplicable Example 5

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This section element has a horizontal scroll distance that is less than its horizontal padding, and vertical scroll distance that is less than its vertical padding.

<section style="height: 210px; width: 530px; overflow: scroll; padding: 30px 0 30px 30px;">
	<div role="heading" aria-level="1">WCAG 2.1 Abstract</div>
	<div style="width: 520px">
		Web Content Accessibility Guidelines (WCAG) 2.1 covers a wide range of recommendations for making Web content more
		accessible. Following these guidelines will make content more accessible to a wider range of people with
		disabilities, including accommodations for blindness and low vision, deafness and hearing loss, limited movement,
		speech disabilities, photosensitivity, and combinations of these, and some accommodation for learning disabilities
		and cognitive limitations; but will not address every user need for people with these disabilities. These guidelines
		address accessibility of web content on desktops, laptops, tablets, and mobile devices. Following these guidelines
		will also often make Web content more usable to users in general.
	</div>
</section>

Inapplicable Example 6

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This iframe element is not a scrollable element, but instead contains a nested browsing context that is scrollable. These must be tested separately.

<iframe src="https://www.w3.org/TR/WCAG21/#abstract" width="500" height="200"></iframe>

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 either Image Button (the state) or image (the keyword mapping to it), both formulations having the same meaning; similarly, “an input element with a type attribute value of Text” 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 and false otherwise. Thus <button disabled>, <button disabled="disabled"> and <button disabled=""> all have a disabled attribute value of true.
• 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.

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.

Scrollable Elements

A scrollable element is an element with a horizontal scroll distance or a vertical scroll distance greater than 0.

• horizontal scroll distance: The difference between scrollWidth and clientWidth for elements where the computed overflow-x is auto or scroll. Undefined for other elements.

• vertical scroll distance: The difference between scrollHeight and clientHeight for elements where the computed overflow-y is auto or scroll. Undefined for other elements.

note: Elements such as iframe which can render a nested browsing context are not scrollable elements. The scrollbars on some iframe elements come from the content inside the nested browsing context.

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.

Rule Versions

1. Proposed version, 30 August 2023 (compare)
2. Latest version, 30 August 2023

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
Axe DevTools Pro 4.37.1	Semi-automated tool	Consistent
Axe-core 4.8.3	Automated tool	Consistent
QualWeb 3.0.0	Automated tool	Consistent
SortSite 6.45	Automated tool	Consistent
Total Validator (+Browser) 17.4.0	Automated tool	Consistent

Useful Links

• Github issues related to this rule
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