HTML page lang and xml:lang attributes have matching values

Rule Type:
atomic
Rule ID:
5b7ae0
Last modified:
March 5, 2020
Accessibility Requirements Mapping
3.1.1 Language of Page (Level A)
  • Required for conformance to WCAG 2.0 and above on level A and above
  • Outcome mapping:
    • Any failed outcomes: success criterion is not satisfied
    • All passed outcomes: success criterion needs further testing
    • An inapplicable outcome: success criterion needs further testing
Input Aspects
DOM Tree

Description

This rule checks that all HTML pages with both a lang and xml:lang attributes on the root element, have the same primary language subtag.

Applicability

This rule applies to any document element if it is an html element that:

Note: html elements within iframe and object elements are not applicable as iframe and object elements create nested browsing contexts. However, as these elements are meant to provide a layer of isolation, the declared language of their parent browsing context will likely not be inherited, making it possible for non-matching lang and xml:lang attributes in nested browsing contexts to also cause accessibility issues.

Expectation

For each test target, the values of the primary language subtags, if any exist, for the lang and xml:lang attributes are the same.

Note: Having matching primary language subtags of the lang and xml:lang attribute, but non-matching language tags overall, will not cause accessibility issues unless there’s a sufficiently large difference between the two language tags. One notable case is the language tags for Cantonese (zh-yue) and Mandarin (zh-cmn) where the primary language subtags match, but the extended language subtags don’t. Such a case would not fail this rule, but could lead to accessibility issues in practice.

Assumptions

Accessibility Support

Since most assistive technologies will consistently use lang over xml:lang when both are used, violation of this rule may not necessarily be a violation of WCAG 2. Only when there are inconsistencies between assistive technologies as to which attribute is used to determine the language does this lead to a violation of SC 3.1.1.

Background

Test Cases

Passed

Passed Example 1

This html element has identical primary language subtags for its lang and xml:lang attributes.

<html lang="en" xml:lang="en"></html>

Passed Example 2

This html element has identical primary language subtags for its lang and xml:lang attributes. The extended language subtags also match.

<html lang="en-GB" xml:lang="en-GB"></html>

Passed Example 3

This html element has identical primary language subtags for its lang and xml:lang attributes. The extended language subtags do not match, but this is not required by this rule.

<html lang="en-GB" xml:lang="en-US"></html>

Failed

Failed Example 1

This html element has different primary language subtags for its lang and xml:lang attributes.

<html lang="fr" xml:lang="en"></html>

Failed Example 2

This html element has different primary language subtags for its lang and xml:lang attributes. The extended language subtags do match, but this rules only focus on the primary language subtags.

<html lang="fr-CA" xml:lang="en-CA"></html>

Inapplicable

Inapplicable Example 1

This rule does not apply to svg elements.

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

Inapplicable Example 2

This rule does not apply to svg elements, even inside an html element.

<html>
	<body>
		<svg lang="en"></svg>
	</body>
</html>

Inapplicable Example 3

This rule does not apply to math elements.

<math xml:lang="en"></math>

Inapplicable Example 4

This rule only applies to documents with a content type of text/html

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html lang="en" xml:lang="en"></html>

Inapplicable Example 5

This rule does not apply to html elements whose lang attribute is not a valid language subtag.

<html lang="em" xml:lang="en"></html>

Inapplicable Example 6

This rule does not apply to html elements without an xml:lang attribute.

<html lang="en"></html>

Inapplicable Example 7

This rule applies neither to html elements without an xml:lang attribute, nor to html in nested browsing context

<html lang="en">
	<iframe srcdoc="<html lang='en' xml:lang='en'></html>" />
</html>

Inapplicable Example 8

This rule does not apply to html elements with an empty ("") xml:lang attribute.

<html lang="fr" xml:lang=""></html>

Glossary

Outcome

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: Implementers 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 Subtag

A language tag consists of a [primary language subtag][] from the language subtag registry, optionally followed by a hyphen (-) and any sequence of characters.

Note: This definition intentionally differs from the BCP 47 syntax 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. As a consequence of this definition, however, grandfathered tags are not correctly recognized as valid language subtags.

Acknowledgements

Authors

Previous Authors

Back to Top