HTML page lang attribute has valid language tag

  • Rule Type:atomic
  • Rule Id: bf051a
  • Last modified: Oct 23, 2020
  • 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 needs further testing.
        • 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 needs further testing.
        • An inapplicable outcome: technique needs further testing.
  • Input Aspects:


This rule checks that the lang attribute of the root element of a non-embedded HTML page has a language tag with a known primary language subtag.


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


For each test target, the lang attribute has a valid language tag.


  • 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.

Accessibility Support

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


This rule is only applicable to non-embedded HTML pages. HTML pages embedded into other documents, such as through iframe or object elements are not applicable because they are not web pages according to the definition in WCAG.

Test Cases


Passed Example 1

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This html element has a lang attribute whose value is a valid primary language subtag.

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

Passed Example 2

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This html element has a lang attribute value that is a valid language tag even though the region subtag is not.

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


Failed Example 1

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This html element has a lang attribute whose value is not a valid language tag.

<html lang="em-US"></html>

Failed Example 2

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This html element has a lang attribute whose value is not a valid language tag.

<html lang="#1"></html>


Inapplicable Example 1

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This rule does not apply to svg elements.

<svg xmlns="" lang="fr"></svg>



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 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.

Useful Links


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.

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