All ACT Rules

HTML page lang attribute has valid language tag

Applicability

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

has a lang attribute that is neither empty ("") nor only ASCII whitespace; and
is in a top-level browsing context; and
has a node document with a content type of text/html.

Expectation

For each test target, the lang attribute has a [known primary language tag][].

Assumptions

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 [known primary language tags][known primary language tag] even if these do not conform to the [RFC 5646][] syntax.
This rule assumes that only [known primary language tags][known primary language tag] are enough to satisfy [Success Criterion 3.1.1 Language of Page][sc311]; this notably excludes [grandfathered tags][] and [ISO 639.2][] three-letters codes, both having poor support in assistive technologies.

Accessibility Support

There are no accessibility support issues known.

Background

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.

Related rules

Bibliography

Test Cases

Passed

Passed Example 1

This html element has a lang attribute with a [known primary language tag][].

<html lang="FR"></html>

Passed Example 2

This html element has a lang attribute with a [known primary language tag][] even though the [region subtag][] is not.

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

Failed

Failed Example 1

This html element has a lang attribute with a [known primary language tag][].

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

Failed Example 2

This html element has a lang attribute with a [known primary language tag][].

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

Failed Example 3

The lang attribute of this page is an [iso 639.2][] three letters code, which has no [known primary language tag][].

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

Failed Example 4

The lang attribute of this page is a [grandfathered tag][grandfathered tags], which has no [known primary language tag][].

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

Inapplicable

Inapplicable Example 1

This rule does not apply to svg elements.

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

AI Prompt

Create a PHP class in the namespace "App\Services\AccessibilityAnalyzer\ActRules"
that extends "App\Services\AccessibilityAnalyzer\ActRuleRunner" and is called "HtmlPageLangValidBf051a" that has a function with the signature "protected function findApplicableElements(Crawler $crawler): Crawler". The base class includes the function "protected function isElementIncludedInAccessibilityTree(\DOMNode $element): bool" for determining if an element is included in the accessibility tree.

Web accessibility rule:

# HTML page lang attribute has valid language tag

metadata:
    id: bf051a
    name: 'HTML page lang attribute has valid language tag'
    rule_type: atomic
    description: "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.\n"
    accessibility_requirements: { 'wcag20:3.1.1': { forConformance: true, failed: 'not satisfied', passed: 'further testing needed', inapplicable: 'further testing needed' }, 'wcag-technique:H57': { forConformance: false, failed: 'not satisfied', passed: 'further testing needed', inapplicable: 'further testing needed' } }
    input_aspects: ['DOM Tree']
    acknowledgments: { authors: ['Jey Nandakumar'], previous_authors: ['Annika Nietzio'], funding: [WAI-Tools] }

## Applicability

This rule applies to any [document element](https://dom.spec.whatwg.org/#document-element) if it is an `html` element for which all the following are true:

- has a `lang` attribute that is neither empty ("") nor only [ASCII whitespace](https://infra.spec.whatwg.org/#ascii-whitespace); and
- is in a [top-level browsing context](https://html.spec.whatwg.org/#top-level-browsing-context); and
- has a [node document](https://dom.spec.whatwg.org/#concept-node-document) with a [content type](https://dom.spec.whatwg.org/#concept-document-content-type) of `text/html`.

## Expectation

For each test target, the `lang` attribute has a [known primary language tag][].

## Assumptions

- 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](https://www.w3.org/TR/WCAG22/#language-of-page).

- This rule assumes that user agents and assistive technologies can programmatically determine [known primary language tags][known primary language tag] even if these do not conform to the [RFC 5646][] syntax.

- This rule assumes that only [known primary language tags][known primary language tag] are enough to satisfy [Success Criterion 3.1.1 Language of Page][sc311]; this notably excludes [grandfathered tags][] and [ISO 639.2][] three-letters codes, both having poor support in assistive technologies.

## Accessibility Support

There are no accessibility support issues known.

## Background

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](https://www.w3.org/TR/WCAG22/#dfn-web-page-s) according to the definition in WCAG.

### Related rules

- [HTML page has `lang` attribute](https://www.w3.org/WAI/standards-guidelines/act/rules/b5c3f8/)
- [HTML page language subtag matches default language](https://www.w3.org/WAI/standards-guidelines/act/rules/ucwvc8/)

### Bibliography

- [Understanding Success Criterion 3.1.1: Language of Page](https://www.w3.org/WAI/WCAG22/Understanding/language-of-page.html)
- [H57: Using language attributes on the html element](https://www.w3.org/WAI/WCAG22/Techniques/html/H57)
- [RFC 5646: Tags for Identifying Languages](https://www.rfc-editor.org/rfc/rfc5646.html)
- [The `lang` and `xml:lang` attributes](https://html.spec.whatwg.org/multipage/dom.html#the-lang-and-xml:lang-attributes)

## Test Cases

### Passed

#### Passed Example 1

This `html` element has a `lang` attribute with a [known primary language tag][].

```html
<html lang="FR"></html>
```

#### Passed Example 2

This `html` element has a `lang` attribute with a [known primary language tag][] even though the [region subtag][] is not.

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

### Failed

#### Failed Example 1

This `html` element has a `lang` attribute with a [known primary language tag][].

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

#### Failed Example 2

This `html` element has a `lang` attribute with a [known primary language tag][].

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

#### Failed Example 3

The `lang` attribute of this page is an [iso 639.2][] three letters code, which has no [known primary language tag][].

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

#### Failed Example 4

The `lang` attribute of this page is a [grandfathered tag][grandfathered tags], which has no [known primary language tag][].

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

### Inapplicable

#### Inapplicable Example 1

This rule does not apply to `svg` elements.

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