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Proposed Bypass Blocks of Repeated Content

Description

This rule checks that each page has a mechanism to bypass repeated blocks of content.

Applicability

This rule applies to any HTML web page.

Expectation

For each test target, the outcome of at least one of the following rules is passed:

Assumptions

Accessibility Support

Techniques and solutions that identify blocks of content are sufficient ways of passing Success Criterion 2.4.1 Bypass blocks. They are, however, only beneficial for users who have ways of navigating with this information. For example, adding headings to a document will only help users who can “jump” from heading to heading (such a possibility can be provided by browsers, browsers plugins, screen readers, or other assistive technologies). Techniques and solutions based on links will benefit all users (for example, sighted keyboard users with no other assistive technology) and are therefore recommended.

If the instruments used to pass some of the atomic rules are not keyboard accessible, or not included in the accessibility tree, passing this rule can still leave many users without a way to bypass blocks of repeated content. WCAG’s definition of mechanism has a note saying that it “needs to meet all success criteria for the conformance level claimed”. This includes Success Criterion 2.1.1 Keyboard and Success Criterion 4.1.2 Name, Role, Value which are both at level A.

This rule only checks if there is a way to bypass at least one section of repeated content. On pages with several interleaved repeated and non-repeated content, this is not sufficient to satisfy Success Criterion 2.4.1 Bypass blocks. Checking for more sections to bypass was considered but rejected due to both the added complexity it would create, and the risk of failing on pages that might be correct.

Background

The instruments used to pass this rule (if any), must meet all level A Success Criteria in order to fully satisfy Success Criterion 2.4.1 Bypass Block. These extra requirements are left out of this rule, and should be tested separately.

Bibliography

To avoid using landmarks for the non-repeated content, which would satisfy Success Criterion 2.4.1 Bypass Block, this rule uses <div id="main"> in its test cases to indicate where non-repeating content exists. It is recommended to use the main landmark instead. The aside and nav elements are each a block of repeated content due to the link inside the nav element to a page with similar blocks of content.

Accessibility Requirements Mapping

Input Rules

Outcomes of the following rules are required as input for this rule.

Test Cases

These HTML and Javascript files are used in several examples:

File /test-assets/bypass-blocks-cf77f2/chapter2.html:

<html>
	<head>
		<title>The Three Kingdoms, Chapter 2</title>
	</head>
	<body>
		<nav id="chapters-navigation">
			<h1>Content</h1>
			<ol>
				<li><a href="/test-assets/bypass-blocks-cf77f2/chapter1.html">Chapter 1</a></li>
				<li><a>Chapter 2</a></li>
			</ol>
		</nav>

		<aside id="bio-translator">
			<h1>About the translator</h1>
			<p>Yu Sumei is a professor of English at East China Normal University.</p>
		</aside>
		<aside id="about-book">
			<h1>About the book</h1>
			<p>The Romance of the Three Kingdoms is a 14th century historical novel.</p>
		</aside>

		<main>
			<h1>Zhang Fei Trashes the Inspector in Wrath</h1>
			<p>
				Now this Dong Zhuo, also known as Dong Zhong-ying, was from Lintao in northwest China.
			</p>
		</main>
	</body>
</html>

File /test-assets/bypass-blocks-cf77f2/toggle-display.js:

function toggleHidden(...ids) {
	ids.forEach(id => {
		const element = document.getElementById(id)
		element.style.display = element.style.display === 'none' ? '' : 'none'
	})
}

function hide(id) {
	const element = document.getElementById(id)
	element.style.display = 'none'
}

function show(id) {
	const element = document.getElementById(id)
	element.style.display = ''
}

function toggleVisibility(id) {
	const element = document.getElementById(id)
	element.className = element.className === 'off-screen' ? '' : 'off-screen'
}

function toggleAriaHidden(id) {
	const element = document.getElementById(id)
	element.setAttribute('aria-hidden', (element.getAttribute('aria-hidden') !== 'true').toString())
}

Passed

Passed Example 1

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This HTML web page is passing rule Block of repeated content is collapsible.

<html>
	<head>
		<script src="/test-assets/bypass-blocks-cf77f2/toggle-display.js"></script>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<a href="#" onclick="toggleHidden('chapters-navigation')">Toggle table of content</a>

		<nav id="chapters-navigation">
			<ol>
				<li><a>Chapter 1</a></li>
				<li><a href="/test-assets/bypass-blocks-cf77f2/chapter2.html">Chapter 2</a></li>
			</ol>
		</nav>

		<div id="main">
			<p>
				Unity succeeds division and division follows unity. One is bound to be replaced by the other after a long span
				of time.
			</p>
		</div>
	</body>
</html>

Passed Example 2

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This HTML web page is passing rule Document has heading for non-repeated content.

<html>
	<head>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<nav id="chapters-navigation">
			<ol>
				<li><a>Chapter 1</a></li>
				<li><a href="/test-assets/bypass-blocks-cf77f2/chapter2.html">Chapter 2</a></li>
			</ol>
		</nav>

		<div id="main">
			<h1>Three Heroes Swear Brotherhood at a Feast in the Peach Garden</h1>
			<p>
				Unity succeeds division and division follows unity. One is bound to be replaced by the other after a long span
				of time.
			</p>
		</div>
	</body>
</html>

Passed Example 3

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This HTML web page is passing rule Document has a landmark with non-repeated content.

<html>
	<head>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<nav id="chapters-navigation">
			<ol>
				<li><a>Chapter 1</a></li>
				<li><a href="/test-assets/bypass-blocks-cf77f2/chapter2.html">Chapter 2</a></li>
			</ol>
		</nav>

		<main>
			<p>
				Unity succeeds division and division follows unity. One is bound to be replaced by the other after a long span
				of time.
			</p>
		</main>
	</body>
</html>

Passed Example 4

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This HTML web page is passing rule Document has an instrument to move focus to non-repeated content.

<html lang="en">
	<head>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<a href="#main">Skip to main content</a>
		<a href="/test-assets/bypass-blocks-cf77f2/chapter2.html">Read Chapter 2</a>

		<aside id="about-book">
			<p>The Romance of the Three Kingdoms is a 14th century historical novel.</p>
		</aside>

		<div id="main">
			<p>
				Unity succeeds division and division follows unity. One is bound to be replaced by the other after a long span
				of time.
			</p>
		</div>
	</body>
</html>

Passed Example 5

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This HTML web page is passing rule Document has an instrument to move focus to non-repeated content.

<html lang="en">
	<head>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<nav id="local-navigation">
			<a href="#bio-translator">Skip to translator's biography</a>
			<a href="#about-book">Skip to information about the book</a>
			<a href="#main">Skip to main content</a>
		</nav>

		<aside id="bio-translator">
			<p>Yu Sumei is a professor of English at East China Normal University.</p>
		</aside>
		<aside id="about-book">
			<p>The Romance of the Three Kingdoms is a 14th century historical novel.</p>
		</aside>

		<div id="main">
			<p>
				Unity succeeds division and division follows unity. One is bound to be replaced by the other after a long span
				of time.
			</p>
			<a href="/test-assets/bypass-blocks-cf77f2/chapter2.html">Read Chapter 2</a>
		</div>
	</body>
</html>

Passed Example 6

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This HTML web page is passing rule Document has an instrument to move focus to non-repeated content.

<html lang="en">
	<head>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<aside id="bio-translator">
			<a href="#about-book">Skip to information about the book</a>
			<p>Yu Sumei is a professor of English at East China Normal University.</p>
		</aside>
		<aside id="about-book">
			<a href="#main">Skip to main content</a>
			<p>The Romance of the Three Kingdoms is a 14th century historical novel.</p>
		</aside>

		<div id="main">
			<p>
				Unity succeeds division and division follows unity. One is bound to be replaced by the other after a long span
				of time.
			</p>
			<a href="/test-assets/bypass-blocks-cf77f2/chapter2.html">Read Chapter 2</a>
		</div>
	</body>
</html>

Passed Example 7

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This HTML web page is passing rule Block of repeated content is collapsible because it has no block of repeated content before non-repeated perceivable content. Note that this does not pass Technique SCR28: Using an expandable and collapsible menu to bypass block of content because the block of repeated content which is after the non-repeated content cannot be toggled.

<html lang="en">
	<head>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<div id="main">
			<p>
				Unity succeeds division and division follows unity. One is bound to be replaced by the other after a long span
				of time.
			</p>
		</div>

		<a href="/test-assets/bypass-blocks-cf77f2/chapter2.html">Read Chapter 2</a>

		<aside id="about-book">
			The Romance of the Three Kingdoms is a 14th century historical novel.
		</aside>
	</body>
</html>

Passed Example 8

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This HTML web page is passing rule Document has an instrument to move focus to non-repeated content because the button is such an instrument. Note that it does not pass Technique G1: Adding a link at the top of each page that goes directly to the main content area nor Technique G123: Adding a link at the beginning of a block of repeated content to go to the end of the block because the instrument is a button, not a link.

<html lang="en">
	<head>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<button onclick="location.assign('#main')">Skip to main content</button>

		<aside id="about-book">
			<p>The Romance of the Three Kingdoms is a 14th century historical novel.</p>
		</aside>

		<div id="main">
			<p>
				Unity succeeds division and division follows unity. One is bound to be replaced by the other after a long span
				of time.
			</p>
			<a href="/test-assets/bypass-blocks-cf77f2/chapter2.html">Read Chapter 2</a>
		</div>
	</body>
</html>

Passed Example 9

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This HTML web page is passing rule Document has an instrument to move focus to non-repeated content because the link with target #brewitt-taylor moves focus just before some non-repeated content after repeated content. Note that it does not necessarily pass Technique G124: Adding links at the top of the page to each area of the content because the <div id="main"> element is arguably a single “area of the content”, and the technique requires only one link per such area.

<html>
	<head>
		<title>Comparing translations of the Romance of the Three Kingdoms, Chapter one</title>
	</head>
	<body>
		<nav id="local-navigation">
			<a href="#local-navigation">Skip to local navigation</a>
			<a href="#brewitt-taylor">Skip to Brewitt-Taylor's translation</a>
			<a href="#roberts">Skip to Roberts' translation</a>
			<a href="#yu">Skip to Yu's translation</a>
			<a href="#about-book">Skip to information about the book</a>
		</nav>

		<aside id="about-book">
			<p>The Romance of the Three Kingdoms is a 14th century historical novel.</p>
		</aside>

		<div id="main">
			<p id="brewitt-taylor">
				Three Heroes Swear Brotherhood in the Peach Garden (Translation by Charles Henry Brewitt-Taylor)
			</p>
			<p>
				The world under heaven, after a long period of division, tends to unite; after a long period of union, tends to
				divide.
			</p>

			<p id="roberts">Three Bold Spirits Plight Mutual Faith in the Peach Garden (Translation by Moss Roberts)</p>
			<p>The empire, long divided, must unite; long united, must divide. Thus it has ever been.</p>

			<p id="yu">Three Heroes Swear Brotherhood at a Feast in the Peach Garden (Translation by Yu Sumei)</p>
			<p>
				Unity succeeds division and division follows unity. One is bound to be replaced by the other after a long span
				of time.
			</p>
			<a href="/test-assets/bypass-blocks-cf77f2/chapter2.html">Read Chapter 2</a>
		</div>
	</body>
</html>

Passed Example 10

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This HTML web page is passing rule Document has an instrument to move focus to non-repeated content. Note that it does not necessarily pass Technique G124: Adding links at the top of the page to each area of the content because the both the nav and aside elements are arguably different “areas of the content”, and the technique requires exactly one link per such area.

<html lang="en">
	<head>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<nav id="local-navigation">
			<a href="#local-navigation">Skip to local navigation</a>
			<a href="#main">Skip to main content</a>
		</nav>

		<aside id="about-book">
			<p>The Romance of the Three Kingdoms is a 14th century historical novel.</p>
		</aside>

		<div id="main">
			<p>
				Unity succeeds division and division follows unity. One is bound to be replaced by the other after a long span
				of time.
			</p>
			<a href="/test-assets/bypass-blocks-cf77f2/chapter2.html">Read Chapter 2</a>
		</div>
	</body>
</html>

Passed Example 11

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This HTML web page is passing rule Block of repeated content is collapsible. Note that it does not pass Technique SCR28: Using an expandable and collapsible menu to bypass block of content because the technique requires that the blocks can be toggled on and off, but here they can only be removed.

<html>
	<head>
		<script src="/test-assets/bypass-blocks-cf77f2/toggle-display.js"></script>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<button onclick="hide('chapters-navigation')">Hide table of content</button>

		<nav id="chapters-navigation">
			<ol>
				<li><a>Chapter 1</a></li>
				<li><a href="/test-assets/bypass-blocks-cf77f2/chapter2.html">Chapter 2</a></li>
			</ol>
		</nav>

		<div id="main">
			<p>
				Unity succeeds division and division follows unity. One is bound to be replaced by the other after a long span
				of time.
			</p>
		</div>
	</body>
</html>

Passed Example 12

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This HTML web page is passing rule Document has an instrument to move focus to non-repeated content because the second link is such an instrument. Note that it does not pass Technique G1: Adding a link at the top of each page that goes directly to the main content area because the skip link is not the first focusable element on the page.

<html lang="en">
	<head>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<a href="https://act-rules.github.io/">ACT rules</a>
		<a href="#main">Skip to main content</a>
		<a href="/test-assets/bypass-blocks-cf77f2/chapter2.html">Read Chapter 2</a>

		<aside id="about-book">
			<p>The Romance of the Three Kingdoms is a 14th century historical novel.</p>
		</aside>

		<div id="main">
			<p>
				Unity succeeds division and division follows unity. One is bound to be replaced by the other after a long span
				of time.
			</p>
		</div>
	</body>
</html>

Failed

Failed Example 1

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This HTML web page does not pass any of the input rules.

<html lang="en">
	<head>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<a href="/test-assets/bypass-blocks-cf77f2/chapter2.html">Read Chapter 2</a>

		<aside id="about-book">
			The Romance of the Three Kingdoms is a 14th century historical novel.
		</aside>

		<div id="main">
			<strong style="font-size: 18pt">Three Heroes Swear Brotherhood at a Feast in the Peach Garden</strong>
			<p>
				Unity succeeds division and division follows unity. One is bound to be replaced by the other after a long span
				of time.
			</p>
		</div>
	</body>
</html>

Inapplicable

Inapplicable Example 1

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This document is not an HTML web page.

<svg xmlns="http://www.w3.org/2000/svg">
  <title>This is an SVG</title>
</svg>

Glossary

Block of content

A block of content in an HTML web page is a set of nodes from that page for which all the following are true:

Block of repeated content

A block of content B, inside an HTML web page P, is a block of repeated content if both the following are true:

Equivalent resource

Non-identical resources can still be equivalent resources by equally complying to the expectation formed by the user when navigating to them, thus serving an equivalent purpose. This would usually involve that the advertised key content is the same.

Web pages and documents (e.g. PDFs, office formats etc.) may be equivalent resources, even if the resources:

If all resources cover the user’s expectations equally well, the resources are considered to be equivalent.

Note: The user’s expectations for the resource can be formed by different things, e.g. the name of the link leading to the resource, with or without the context around the link. This depends on the accessibility requirement that is tested.

Note: If the same content is presented in different formats or languages, the format or language itself is often part of the purpose of the content, e.g. an article as both HTML and PDF, an image in different sizes, or an article in two different languages. If getting the same content in different formats or languages is the purpose of having separate links, the resources are not equivalent.

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 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.

Instrument to achieve an objective

An HTML element that when activated allows an end-user to achieve an objective.

Note: Any rule that uses this definition must provide an unambiguous description of the objective the instrument is used to achieve.

Just before a node

A node N is just before a node of perceivable content P if one of the following is true:

Several nodes may be just before a given node, especially if there are several non-perceivable content nodes next to each other.

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.

Non-repeated content after repeated content

A node is non-repeated content after repeated content if all the following are true:

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:

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.

Perceivable content

A node is perceivable content if all the following are true:

Perceivable content corresponds to nodes that contain information and are perceived by some categories of users.

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.

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.

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.

Web page (HTML)

An HTML web page is the set of all fully active documents which share the same top-level browsing context.

Note: Nesting of browsing context mostly happens with iframe and object. Thus a web page will most of the time be a “top-level” document and all its iframe and object (recursively).

Note: Web pages as defined by WCAG are not restricted to the HTML technology but can also include, e.g., PDF or DOCX documents.

Note: Although web pages as defined here are sets of documents (and do not contain other kind of nodes), one can abusively write that any node is “in a web page” if it is a shadow-including descendant of a document that is part of that web page.

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
Axe DevTools Pro 4.37.1 Semi-automated tool Partial Axe DevTools Pro Report
Axe-core 4.8.1 Automated tool Partial Axe-core Report
QualWeb 3.0.0 Automated tool Partial QualWeb Report
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