Block of repeated content is collapsible

  • Rule Type:atomic
  • Rule Id: 3e12e1
  • Last modified: Jan 11, 2022
  • Accessibility Requirements Mapping:
    • SCR28: Using an expandable and collapsible menu to bypass block of content
      • Learn More about technique SCR28
      • Not required to 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.

Description

This rule checks that repeated blocks of content are collapsible

Applicability

This rule applies to any HTML web page.

Expectation

For each block of repeated content in each test target, which is before (in the flat tree) at least one node of non-repeated content after repeated content, all the following are true:

Assumptions

No assumptions.

Accessibility Support

There are no major accessibility support issues known for this rule.

Background

Usually the same instrument removes both visibility and inclusion in the accessibility tree of a block of repeated content. That instrument may remove all blocks of repeated content. If there is no block of repeated content before the non-repeated content the rule passes.

Technique SCR28: Using an expandable and collapsible menu to bypass block of content does not have any requirements concerning the location of the instruments in relation to the block of repeated content they control, hence this rule doesn't. It is likely a good idea to either keep each instrument close to the start of the block of repeated content it controls; or to group them all in one place near the start of the document. Notably, instruments located after (in reading order) the block they collapse are likely not satisfying Success Criterion 2.4.1 Bypass blocks, which this rule is designed for. Thus, it is possible to pass this rule without satisfying Success Criterion 2.4.1 Bypass blocks.

Bibliography

Test Cases

To avoid using landmarks for the non-repeated content, which would satisfy Success Criterion 2.4.1 Bypass Block, which this rule is designed for, 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.

Passed

Passed Example 1

Open in a new tab

This document has a link at the start of the document to toggle the visibility and inclusion in the accessibility tree of the navigational block of repeated content.

<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

Open in a new tab

This document has a button at the start of the document to toggle the visibility and inclusion in the accessibility tree of both the complementary and the navigational blocks of repeated content.

<html>
	<head>
		<script src="/test-assets/bypass-blocks-cf77f2/toggle-display.js"></script>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<button onclick="toggleHidden('chapters-navigation', 'about-book')">Toggle repeated 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>

		<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 3

Open in a new tab

This document has two dedicated instruments to toggle the visibility and inclusion in the accessibility tree of the complementary and the navigational blocks of repeated content respectively.

<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>
		<button onclick="toggleHidden('about-book')">Toggle extra 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>

		<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 4

Open in a new tab

This document has a button at the start of the document to toggle the visibility and inclusion in the accessibility tree of the navigational block of repeated content. The button is only visible when focused.

<html>
	<head>
		<script src="/test-assets/bypass-blocks-cf77f2/toggle-display.js"></script>
		<link rel="stylesheet" href="/test-assets/bypass-blocks-cf77f2/styles.css" />
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<button onclick="toggleHidden('chapters-navigation')" class="visible-on-focus">Toggle repeated 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>

Failed

Failed Example 1

Open in a new tab

This document has no instrument to toggle the navigational block of 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">
			<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 Example 2

Open in a new tab

This document has an instrument to toggle visibility of the navigational block of repeated content, but none to toggle its inclusion in the accessibility tree.

<html>
	<head>
		<link rel="stylesheet" href="/test-assets/bypass-blocks-cf77f2/styles.css" />
		<script src="/test-assets/bypass-blocks-cf77f2/toggle-display.js"></script>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<a href="#" onclick="toggleVisibility('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>

Failed Example 3

Open in a new tab

This document has an instrument to toggle the inclusion on the accessibility tree of the block of repeated content, but none to toggle its visibility.

<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="toggleAriaHidden('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>

Inapplicable

Inapplicable Example 1

Open in a new tab

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:

  • content: there is at least one node which is perceivable content in the block; and
  • continuity: if two nodes are in the block, then any node between them (in tree order) is also in the block; and
  • downward closure: if a node is in the block, then all its descendants are also in the block; and
  • parent closure: if all children of a node are in the block, then this node is also in the block.

Assumptions for Block of content

This definition assumes that the rendering order of nodes on a page does not greatly differ from the DOM tree order. Otherwise, blocks of content as defined here may be different from what is visually perceived as "content in a close relationship".

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:

Background for Block of repeated content

This definition only considers pages at "distance 1" from the current page. The instrument leading there is usually a link, sometimes a button. In addition, P' can be any page and is not restricted, for example, to pages of the same website.

The blocks of repeated content are not uniquely defined. For example <div><span id="repeated-1"></span><span id="repeated-2"></span><span id="not-repeated"></span></div> can be considered to have two blocks of repeated content (each of the first two span) or one (both the first two span together).

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:

  • are located on different URLs, including different domains
  • present different navigation options, e.g. through bread crumbs or local sub menus
  • contain different amounts of information and/or differently worded information
  • use different layouts.

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.

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.

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.

Background About Instrument for Instrument to achieve an objective

This definition is a more restrictive version of WCAG's definition of mechanism, notably restricting it to the current document. WCAG has a note that "The mechanism needs to meet all success criteria for the conformance level claimed." This includes all the level A criteria such as Success Criterion 2.1.1 Keyboard (the mechanism must be keyboard accessible) or Success Criterion 4.1.2 Name, Role, Value (the mechanism must be exposed to assistive technologies and have an accessible name). This definition, and the rules using it, leaves these extra requirements out. This avoids reporting the same component twice for the same reason (e.g., missing an accessible name) under two different rules and Success Criteria, and helps pinpoint the error related to each Success Criterion. Instruments should nonetheless be fully accessible at the correct conformance level (depending on the rule using them).

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.

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.

Assumptions for Perceivable content

This definition assumes that elements with a semantic role of none or presentation are pure decoration and that elements which are pure decoration either are not included in the accessibility tree or have a semantic role of none or presentation. Note that if this is not the case, then Success Criterion 1.3.1: Info and Relationship is likely not satisfied.

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: 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.

Content is defined in WCAG.

For more details, see examples of visible.

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.


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

Acknowledgments

Funding

  • WAI-Tools

Assets

  • _The Three Kingdoms_ by Luo Guanzhong, translation by Yu Sumei (Tuttle publishing, 2014, ISBN 9780804843935)
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