Proposed Test Rule: Document has an instrument to move focus to non-repeated content

Description

This rule checks that there is an instrument to move focus to non-repeated content in the page

Applicability

This rule applies to any HTML web page.

Expectation

For each test target, there exists at least one instrument inside it to move focus just before a node of non-repeated content after repeated content.

Assumptions

This rule assumes that there is at least one block of repeated content before the non-repeated content, and therefore [Technique G123: Adding a link at the beginning of a block of repeated content to go to the end of the block][tech g123] will require a link to the non-repeated content in order to skip this block of repeated content. If there is no block of repeated content before the non-repeated content, then it is possible to fail this rule but still pass [Technique G123: Adding a link at the beginning of a block of repeated content to go to the end of the block][tech g123].
This rule assumes that the language of each test target can be correctly determined (either programmatically or by analyzing the content), and sufficiently understood.

Accessibility Support

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

Background

The intention of this rule is that focus is moved to the main area of content of a document. However, defining the main area of content in a non-ambiguous way is not really doable. Therefore, the rule takes a more lenient position and only requires to move focus to some non-repeated content. Additional conditions on this destination were considered and rejected when writing the rule since it might be acceptable, for example, to skip the first heading of the main area of content if it has the exact same content as the title element of the document. Therefore, it is possible to pass this rule but still fail the related techniques and violate [Success Criterion 2.4.1 Bypass blocks][sc241].

While it is clear that a “skip link” is a valid way to satisfy [Success Criterion 2.4.1 Bypass blocks][sc241], it is less clear how “deep” in the page such a skip link could be. Notably, [Technique G124: Adding links at the top of the page to each area of the content][tech g124] is listing valid cases where it could be fairly “deep” if the page has many areas of the content. Rather than trying to fix an arbitrary value (e.g. “the skip link must be among the first 5 focusable elements”), or trying to figure out some condition on what precedes it, this rule only checks its existence. It is clear that if no “skip link” is provided, then another way to bypass blocks of repeated content must be found. However, it is possible to pass this rule without satisfying [Success Criterion 2.4.1 Bypass blocks][sc241] if the skip link is too far away from the start of the page.

[Technique G1: Adding a link at the top of each page that goes directly to the main content area][tech g1]
[Technique G123: Adding a link at the beginning of a block of repeated content to go to the end of the block][tech g123]
[Technique G124: Adding links at the top of the page to each area of the content][tech g124]

To avoid using landmarks for the non-repeated content, which would satisfy [Success Criterion 2.4.1 Bypass Block][sc241], 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.

Due to the differences between the 3 techniques considered here, it is almost impossible to pass all of them at the same time. The first few Passed Examples illustrate these differences and pass different techniques. The rest of the Passed Examples illustrate variations inside the rule and are based on cases that pass [Technique G1: Adding a link at the top of each page that goes directly to the main content area][tech g1] given that it is simpler than the other two.

The examples sometimes group the skip links inside a nav landmark (notably when there are several). According to WAI-ARIA authoring practices, if another nav landmark was present on the page (e.g. for site navigation), then each should have a different accessible name.

Test Cases

Passed

Passed Example 1

In this document, the first a element is an instrument to navigate, and thus move the focus, to the non-repeated content. This example passes [Technique G1: Adding a link at the top of each page that goes directly to the main content area][tech g1].

<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 2

In this document, the third a element is an instrument to move the focus to the non-repeated content. This example passes [Technique G124: Adding links at the top of the page to each area of the content][tech g124].

<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 3

In this document, the second a element (inside the second aside element) is an instrument to move the focus to the non-repeated content. This example passes [Technique G123: Adding a link at the beginning of a block of repeated content to go to the end of the block][tech g123].

<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 4

In this document, the first a element is an instrument to move the focus to the non-repeated content. In this case, the element is normally hidden but is [visible][] when focused.

<html lang="en">
	<head>
		<link rel="stylesheet" href="/test-assets/bypass-blocks-cf77f2/styles.css" />
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<nav class="visible-on-focus">
			<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 5

In this document, the first div element is an instrument to move the focus to the non-repeated content.

<html lang="en">
	<head>
		<script src="/test-assets/bypass-blocks-cf77f2/click-on-enter.js"></script>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body onload="ClickOnEnter('skip-link')">
		<div role="link" onclick="location.assign('#main');" tabindex="0" id="skip-link">Skip to main content</div>

		<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

In this document, the first a element is an instrument to move the focus to the non-repeated content.

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

Passed Example 7

In this document, the first a element is an instrument to move the focus to the non-repeated content. Even though its target is inside a block of repeated content, it is still just before some non-repeated content after repeated content because there is no perceivable content between the link target and the non-repeated content. Thus, following the link does skip all the repeated content.

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

		<aside id="about-book">
			<p>The Romance of the Three Kingdoms is a 14th century historical novel.</p>
			<span id="just-before-main"></span>
		</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 8

In this document, the first a element is an instrument to move the focus to the non-repeated content. Even though its target is not the first element after it, it is still just before the first non-repeated content after repeated content. Thus, following the link does not skip any non-repeated content.

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

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

		<div id="main">
			<hr />
			<span id="just-before-main"></span>
			<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>

Failed

Failed Example 1

This document has no instrument to skip to the non-repeated content.

<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">
			<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 Example 2

In this document, the link to skip to the non-repeated content does not reference a valid id attribute and thus when activated will not move focus to the non-repeated content.

<html lang="en">
	<head>
		<title>The Three Kingdoms, Chapter 1</title>
	</head>
	<body>
		<a href="#invalid-id">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 Example 3

In this document, the skip link does not move focus just before some non-repeated content after repeated content. The focus is moved on perceivable content which is inside the block of repeated content. Thus, following the link does not skip all the repeated content.

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

		<aside id="about-book">
			<p id="before-main">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>

Inapplicable

Inapplicable Example 1

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.

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:

distance 1: there exist an instrument in P which leads the user to another HTML web page P’ whose URL has a different host, port (including default port for [special URL][]), or path; and
repeated: there exist a block of content in P’ which is equivalent to B.

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.

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

Elements that can become the target of keyboard input as described in the HTML specification of focusable and can be focused.

Hidden State

An HTML element’s hidden state is “true” if at least one of the following is true for itself or any of its ancestors in the flat tree:

has a hidden attribute; or
has a computed CSS property display of none; or
has a computed CSS property visibility of hidden; or
has an aria-hidden attribute set to true

In any other case, the element’s hidden state is “false”.

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. Elements in the accessibility tree are exposed to assistive technologies, allowing users to interact with the elements in a way that meet 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][].

Note: Users of assistive technologies might still be able to interact with elements that are not included in the accessibility tree. An example of this is a focusable element with an aria-hidden attribute with a value of true. Such an element could still be interacted using sequential keyboard navigation regardless of the assistive technologies used, even though the element would not be included in the accessibility tree. [examples of included in the accessibility tree]: https://act-rules.github.io/pages/examples/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:

N and P are the same node; or
N is not perceivable content and there is no node of perceivable content between N and P (in [tree order][] in the flat tree).

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:

it has an explicit role of none or presentation; or
it is an img element with an alt attribute whose value is the empty string (alt=""), and with no explicit role.

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 their hidden state is true. This is different from marking the element as decorative and does not convey the same intention. Notably, the hidden state of an element 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:

the node is perceivable content; and
the node is not part of any block of repeated content; and
the node is after (in [tree order][] in the flat tree) at least one block of repeated content.

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:

the node is palpable content; and
the node is either [visible][] or included in the accessibility tree; and
if the node is an element, it does not have a [semantic role][] of none or presentation.

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

Semantic Role

The semantic role of an element is determined by the first of these cases that applies:

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 its hidden state is false, then its semantic role is its implicit role.
Explicit If the element has an explicit role, then its semantic role is its explicit role.
Implicit The semantic role of the element is its implicit role.

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.

Implementations

There are currently no known implementations for this rule. If you would like to contribute an implementation, please read the ACT Implementations page for details.

Changelog

This is the first version of this ACT rule.

[sc131]: https://www.w3.org/TR/WCAG21/#info-and-relationships ‘Success Criterion 1.3.1 [sc211]: https://www.w3.org/TR/WCAG21/#keyboard ‘Success Criterion 2.1.1 Keyboard’ [sc241]: https://www.w3.org/TR/WCAG21/#bypass-blocks ‘Success Criterion 2.4.1 Bypass Blocks’ [sc412]: https://www.w3.org/TR/WCAG21/#name-role-value ‘Success Criterion 4.1.2 Name, Role, Value’ [semantic role]: #semantic-role ‘Definition of semantic role’ [special url]: https://url.spec.whatwg.org/#is-special ‘URL specification of Special URL’ [tech g123]: https://www.w3.org/WAI/WCAG21/Techniques/general/G123 ‘Technique G123 [tech g124]: https://www.w3.org/WAI/WCAG21/Techniques/general/G124 ‘Technique G124 [tech g1]: https://www.w3.org/WAI/WCAG21/Techniques/general/G1 ‘Technique G1 [tree order]: https://dom.spec.whatwg.org/#concept-tree-order ‘DOM specification of Tree Order’ [visible]: #visible ‘Definition of Visible’ [wai-aria specifications]: #wai-aria-specifications ‘Definition of WAI-ARIA specifications’