HTML page language subtag matches default language

  • Rule Type:atomic
  • Rule Id: ucwvc8
  • Last modified: Oct 14, 2021
  • Accessibility Requirements Mapping:
    • 3.1.1 Language of Page (Level A)
      • Learn More about 3.1.1 Language of Page
      • 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 is satisfied.
        • An inapplicable outcome: success criterion needs further testing.
    • H57: Using language attributes on the html element
      • Learn More about technique H57
      • Not required to conformance to any W3C accessibility recommendation.
      • Outcome mapping:
        • Any failed outcomes: technique is not satisfied.
        • All passed outcomes: technique is satisfied.
        • An inapplicable outcome: technique is satisfied.

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:

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 RFC 5646 syntax.
  • This rule assumes that only valid language tags are enough to satisfy Success Criterion 3.1.1 Language of Page; this notably excludes grandfathered tags and ISO 639.2 three-letters codes, both having poor support in assistive technologies.
  • 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

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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

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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

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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

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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

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This page has a lang attribute value of da (Danish), which does not match 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

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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

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This page has a lang attribute value of en (English), which does not match 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

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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

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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

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This is an SVG document, not an HTML document.

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

Inapplicable Example 2

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

<html></html>

Inapplicable Example 3

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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

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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>

Inapplicable Example 5

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The lang attribute value of this page is an iso 639.2 three letters code, hence not a valid language tag.

<html lang="eng">
	<body>
		<p lang="en">I love ACT rules!</p>
	</body>
</html>

Inapplicable Example 6

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The lang attribute value of this page is a grandfathered tag, hence not a valid language tag.

<html lang="i-lux">
	<body>
		<p lang="lb">Lëtzebuerg ass e Land an Europa.</p>
	</body>
</html>

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.

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.

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 RFC 5646 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 RFC 5646 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 RFC 5646 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.

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.

No Implementations

Implementation reports are not provided for this rule.

Acknowledgments

Funding

  • WAI-Tools
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