Proposed Test Rule: HTML page language subtag matches default language

Description

This rule checks that the primary language subtag of the page language matches the default language of the page

Applicability

This rule applies to any document element if it is an html element for which all of the following are true:

The document element has a lang attribute with a value that is a valid language tag; and
The document element is in a top-level browsing context; and
The document element has a content type of text/html; and
The document element has a defined default page language.

Expectation

For each test target, the primary language of the valid language tag matches the default page language of the test target.

Assumptions

This rule assumes that the default human language of a page, as described in WCAG 2, can be determined by counting the number of words used in each language. If the default language needs to be derived in some other way (such as frequency analysis, mutual information based distance, …), this rule may fail while Success Criterion 3.1.1: Language of Page is still satisfied.
The language of the page can be set by other methods than the lang attribute, for example using HTTP headers or the meta element. These methods are not supported by all assistive technologies. This rule assumes that these other methods are insufficient to satisfying Success Criterion 3.1.1: Language of Page.
This rule assumes that user agents and assistive technologies can programmatically determine valid language tags even if these do not conform to the BCP 47 syntax.
This rule assumes that grandfathered tags are not used as these will not be recognized as valid language tags.
This rule assumes that iframe title elements are not exposed to assistive technologies and so does not consider them as part of the default page language.

Accessibility Support

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

Background

Test Cases

Passed

Passed Example 1

This page has a lang attribute value of en (English), which matches the default language of the page. The default language is English because all words are English.

<html lang="en">
	<head>
		<title>ACT Rules Format 1.0 - Abstract</title>
	</head>
	<body>
		<p>
			The Accessibility Conformance Testing (ACT) Rules Format 1.0 defines a format for writing accessibility test
			rules. These test rules can be used for developing automated testing tools and manual testing methodologies. It
			provides a common format that allows any party involved in accessibility testing to document and share their
			testing procedures in a robust and understandable manner. This enables transparency and harmonization of testing
			methods, including methods implemented by accessibility test tools.
		</p>
	</body>
</html>

Passed Example 2

This page has a lang attribute value of en (English), which matches the default language of the page. The default language is English because all but a few words are English.

<html lang="en">
	<head>
		<title>Gelukkig</title>
	</head>
	<body>
		<p>The Dutch word "gelukkig" has no equivalent in English.</p>
	</body>
</html>

Passed Example 3

This page has lang attribute value of nl (Dutch), which matches the default language of the page. The default language is Dutch because all English words are in a p element with a lang attribute value of en.

<html lang="nl">
	<head>
		<title>Met de kippen op stok</title>
	</head>
	<body>
		<blockquote>
			<p>"Hij ging met de kippen op stok"</p>
		</blockquote>
		<p lang="en">
			This Dutch phrase literally translates into "He went to roost with the chickens", but it means that he went to bed
			early.
		</p>
	</body>
</html>

Passed Example 4

This page has a lang attribute value of en (English), which matches the default language of the page. The default language is English because the accessible texts are English, and all other text is in a p element with a lang attribute value of nl.

<html lang="en">
	<head>
		<title>Fireworks over Paris</title>
	</head>
	<body>
		<img src="/test-assets/shared/fireworks.jpg" alt="Fireworks over Paris" />
		<p lang="nl">
			Gelukkig nieuwjaar!
		</p>
	</body>
</html>

Failed

Failed Example 1

This page has lang attribute value of da (Danish), which does not matches the default language of the page. The default language is English because all words are English.

<html lang="da">
	<head>
		<title>ACT Rules Format 1.0 - Abstract</title>
	</head>
	<body>
		<p>
			The Accessibility Conformance Testing (ACT) Rules Format 1.0 defines a format for writing accessibility test
			rules. These test rules can be used for developing automated testing tools and manual testing methodologies. It
			provides a common format that allows any party involved in accessibility testing to document and share their
			testing procedures in a robust and understandable manner. This enables transparency and harmonization of testing
			methods, including methods implemented by accessibility test tools.
		</p>
	</body>
</html>

Failed Example 2

This page has a lang attribute value of nl (Dutch), which does not match the default language of the page. The default language is English because all but a few words are English.

<html lang="nl">
	<head>
		<title>Gelukkig</title>
	</head>
	<body>
		<p>The Dutch word "gelukkig" has no equivalent in English.</p>
	</body>
</html>

Failed Example 3

This page has lang attribute value of en (English), which does not matches the default language of the page. The default language is Dutch because all English words are in a p element with a lang attribute value of en.

<html lang="en">
	<head>
		<title>Met de kippen op stok</title>
	</head>
	<body>
		<blockquote>
			<p>"Hij ging met de kippen op stok"</p>
		</blockquote>
		<p lang="en">
			This Dutch phrase literally translates into "He went to roost with the chickens", but it means that he went to bed
			early.
		</p>
	</body>
</html>

Failed Example 4

This page has a lang attribute value of nl (Dutch), which does not match the default language of the page. The default language is English because the accessible texts are English, and all other text is in a p element with a lang attribute value of nl.

<html lang="nl">
	<head>
		<title>Fireworks over Paris</title>
	</head>
	<body>
		<img src="/test-assets/shared/fireworks.jpg" alt="Fireworks over Paris" />
		<p lang="nl">
			Gelukkig nieuwjaar!
		</p>
	</body>
</html>

Failed Example 5

This page has a lang attribute value of nl (Dutch), which does not match the default language of the page. The default language is English because the accessible name of the img element is English. The lang attribute on the p element is effectively ignored.

<html lang="nl">
	<head>
		<title>Paris</title>
	</head>
	<body>
		<img src="/test-assets/shared/fireworks.jpg" aria-labelledby="caption" />
		<p lang="en" id="caption" hidden>
			Fireworks over Paris!
		</p>
	</body>
</html>

Inapplicable

Inapplicable Example 1

This is an SVG document, not an HTML document.

<svg xmlns="http://www.w3.org/2000/svg" lang="fr"></svg>

Inapplicable Example 2

This page has an undefined default language because it has no content or document title.

<html></html>

Inapplicable Example 3

This page has an undefined default language because it has no document title and all its content is wrapped in an element with a lang attribute.

<html>
	<p lang="en">
		The Accessibility Conformance Testing (ACT) Rules Format 1.0 defines a format for writing accessibility test rules.
		These test rules can be used for developing automated testing tools and manual testing methodologies. It provides a
		common format that allows any party involved in accessibility testing to document and share their testing procedures
		in a robust and understandable manner. This enables transparency and harmonization of testing methods, including
		methods implemented by accessibility test tools.
	</p>
</html>

Inapplicable Example 4

This page has an undefined default language because it can either be English or French.

<html lang="fr">
	<head>
		<title>Paul put dire comment on tape</title>
	</head>
	<body>
		<p>Paul put dire comment on tape</p>
	</body>
</html>

Glossary

Accessible Name

The accessible name is the programmatically determined name of a user interface element that is included in the accessibility tree.

The accessible name is calculated using the accessible name and description computation.

For native markup languages, such as HTML and SVG, additional information on how to calculate the accessible name can be found in HTML Accessibility API Mappings 1.0, Accessible Name and Description Computation (working draft) and SVG Accessibility API Mappings, Name and Description (working draft).

For more details, see examples of accessible name.

Note: As per the accessible name and description computation, each element always has an accessible name. When no accessible name is provided, the element will nonetheless be assigned an empty ("") one.

Note: As per the accessible name and description computation, accessible names are flat string trimmed of leading and trailing whitespace. Notably, it is not possible for a non-empty accessible name to be composed only of whitespace since these must be trimmed.

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.

Default Page Language

The default language of a web page is the most common language of its top-level browsing context document, if it is unique. If this document has either no or several most common languages, then it has no default language.

For more details, see examples of default language.

Focusable

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

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/

Most Common Language of an Element

The most common language of an element is determined by counting the number of words in the text inheriting its programmatic language from this element that are part of any of the languages in the language subtag registry. The same word can be part of multiple languages. In case of ties, the element has several most common languages. If there are no words in the text inheriting its programmatic language from the element, then it has no most common language.

For more details, see examples of most common language.

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.

Text Inheriting its Programmatic Language from an Element

The text inheriting its programmatic language from an element E is composed of all the following texts:

text nodes: the value of any text nodes that are visible or included in the accessibility tree and children of an element inheriting its programmatic language from E;
accessible text: the accessible name and accessible description of any element inheriting its programmatic language from E, and included in the accessibility tree;
page title: the value of the document title, only if E is a document in a top-level browsing context.

An element F is an element inheriting its programmatic language from an element E if at least one of the following conditions is true (recursively):

F is E itself (an element always inherits its programmatic language from itself); or
F does not have a non-empty lang attribute, and is the child in the flat tree of an element inheriting its programmatic language from E; or
F is a fully active document element, has no non-empty lang attribute, and its browsing context container is an element inheriting its programmatic language from E.

Valid Language Tag

A language tag is valid if its primary language subtag exists in the language subtag registry with a Type field whose field-body value is language.

A “language tag” is here to be understood as in the first paragraph of the BCP 47 language tag syntax, i.e. a sequence of subtags separated by hyphens, where a subtag is any sequence of alphanumerical characters. Thus, this definition intentionally differs from the strict BCP 47 syntax (and ABNF grammar) as user agents and assistive technologies are more lenient in what they accept. The definition is however consistent with the behavior of the :lang() pseudo-selector as defined by Selectors Level 3. For example, de-hello would be an accepted way to indicate German in current user agents and assistive technologies, despite not being valid according to BCP 47 grammar. As a consequence of this definition, however, grandfathered tags are not correctly recognized as valid language subtags.

Subtags, notably the primary language subtag, are case insensitive. Hence comparison with the language subtag registry must be done in a case insensitive way.

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.

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.