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Adjust definition of valid language subtag (de46e4, bf051a, 5b7ae0) #1106

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Feb 20, 2020
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Adjust definition of valid language subtag (de46e4, bf051a, 5b7ae0) #1106

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a361252
Adjust definition of valid language subtag
kasperisager Jan 20, 2020
92866b0
Add missing references
kasperisager Jan 20, 2020
9a30e6a
Update pages/glossary/valid-language-subtag.md
kasperisager Jan 22, 2020
c5980ba
Add some spelling ignores
kasperisager Jan 30, 2020
1545adc
Add missing word
kasperisager Jan 30, 2020
5041f05
Merge remote-tracking branch 'origin/develop' into lang-syntax-requir…
kasperisager Jan 31, 2020
559cb4d
Merge branch 'develop' into lang-syntax-requirement
Jym77 Jan 31, 2020
0ed0653
Update spelling list
kasperisager Feb 4, 2020
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3 changes: 3 additions & 0 deletions __tests__/spelling-ignore.yml
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Expand Up @@ -37,6 +37,8 @@
- DOCX
- DPUB
- DNS
- BCP
- bcp
- Esc # esc key on a keyboard
- url
- voiceover
Expand All @@ -60,6 +62,7 @@
- EARL10-Schema
- labelable
- merchantability
- de-hello
- 14pt
- 18pt
- Helvetica
Expand Down
27 changes: 17 additions & 10 deletions _rules/element-lang-valid-de46e4.md
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Expand Up @@ -32,7 +32,11 @@ For each test target, the `lang` attribute has a [valid language subtag](#valid-

## Assumptions

This rule assumes that the presence of a `lang` attribute is being used to comply to WCAG. This rule doesn't test if the attribute is needed to comply to WCAG.
- This rule assumes that the presence of a `lang` attribute is being used to comply to WCAG. This rule doesn't test if the attribute is needed to comply to WCAG.

- This rule assumes that user agents and assistive technologies can programmatically determine [valid language subtags](#valid-language-subtag) 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 subtags](#valid-language-subtag).

## Accessibility Support

Expand Down Expand Up @@ -73,33 +77,33 @@ The `lang` attribute has a value that is not empty ("") and has a valid primary
</html>
```

### Failed

#### Failed Example 1
#### Passed Example 3

The `lang` attribute value is not a valid primary language subtag.
The `lang` attribute value has a valid primary language subtag, but a syntactically invalid region subtag.

```html
<html>
<body>
<article lang="dutch"></article>
<p lang="en-US-GB"></p>
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This is right - BCP 47 has an algorithm for determining best matching language in 'Matching of Language Tags' at the end of BCP 47:

In the lookup scheme, the language range is progressively truncated
from the end until a matching language tag is located

So lookup order is en-US-GB to en-US to en

</body>
</html>
```

#### Failed Example 2
### Failed

The `lang` attribute value has a valid primary language subtag, but a syntactically invalid region subtag.
#### Failed Example 1

The `lang` attribute value is not a valid primary language subtag.

```html
<html>
<body>
<p lang="en-US-GB"></p>
<article lang="dutch"></article>
</body>
</html>
```

#### Failed Example 3
#### Failed Example 2

The `lang` attribute value is not empty ("") and is not a valid primary language subtag.

Expand Down Expand Up @@ -148,3 +152,6 @@ The `lang` attribute value consists of only [ASCII whitespace](https://infra.spe
</body>
</html>
```

[grandfathered tags]: https://tools.ietf.org/html/bcp47#section-2.2.8
[bcp 47]: https://tools.ietf.org/html/bcp47#section-2.1
26 changes: 16 additions & 10 deletions _rules/html-page-lang-valid-bf051a.md
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Expand Up @@ -34,7 +34,11 @@ For each test target, the `lang` attribute has a [valid language subtag](#valid-

## Assumptions

This rule assumes that the presence of a `lang` attribute is being used to comply to WCAG. This rule doesn't test if the attribute is needed to comply to WCAG.
- This rule assumes that the presence of a `lang` attribute is being used to comply to WCAG. This rule doesn't test if the attribute is needed to comply to WCAG.

- This rule assumes that user agents and assistive technologies can programmatically determine [valid language subtags](#valid-language-subtag) even if these do not conform to the [BCP 47][] syntax.
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This is a reasonable assumption - BCP 47 has an algorithm for determining best matching language in 'Matching of Language Tags' at the end of BCP 47:

In the lookup scheme, the language range is progressively truncated
from the end until a matching language tag is located

Even if an implementor hasn't read this part of the spec, it's still likely they'll implement it because it's easy to implement and fairly obvious.


- This rule assumes that [grandfathered tags][] are not used as these will not be recognized as [valid language subtags](#valid-language-subtag).

## Accessibility Support

Expand All @@ -59,6 +63,14 @@ This `html` element has a `lang` attribute whose value is a [valid][valid langua
<html lang="fr"></html>
```

#### Passed Example 2

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

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

### Failed

#### Failed Example 1
Expand All @@ -71,21 +83,13 @@ This `html` element has a `lang` attribute whose value is not a [valid language

#### Failed Example 2

This `html` element has a `lang` attribute whose value is not a [valid language subtag][]. Even though the [primary language subtag][] is valid, the [region subtag] is not.

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

#### Failed Example 3

This `html` element has a `lang` attribute whose value is not a [valid language subtag][].

```html
<html lang="123"></html>
```

#### Failed Example 4
#### Failed Example 3

This `html` element has a `lang` attribute whose value is not a [valid language subtag][].

Expand All @@ -106,3 +110,5 @@ This rule does not apply to `svg` elements.
[primary language subtag]: https://tools.ietf.org/html/bcp47#section-2.2.1 'Definition of primary language subtag'
[region subtag]: https://tools.ietf.org/html/bcp47#section-2.2.4 'Definition of region subtag'
[valid language subtag]: #valid-language-subtag 'Definition of valid language subtag'
[grandfathered tags]: https://tools.ietf.org/html/bcp47#section-2.2.8
[bcp 47]: https://tools.ietf.org/html/bcp47#section-2.1
8 changes: 7 additions & 1 deletion _rules/html-page-lang-xml-lang-match-5b7ae0.md
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Expand Up @@ -38,7 +38,11 @@ For each test target, the values of the [primary language subtags](https://tools

## Assumptions

This rule assumes that the presence of a `lang` attribute is being used to comply to WCAG. This rule doesn't test if the attribute is needed to comply to WCAG.
- This rule assumes that the presence of a `lang` attribute is being used to comply to WCAG. This rule doesn't test if the attribute is needed to comply to WCAG.

- This rule assumes that user agents and assistive technologies can programmatically determine [valid language subtags](#valid-language-subtag) 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 subtags](#valid-language-subtag).

## Accessibility Support

Expand Down Expand Up @@ -153,3 +157,5 @@ This rule does not apply to `math` elements.
[extended language subtags]: https://tools.ietf.org/html/bcp47#section-2.2.2 'Definition of extended language subtag'
[primary language subtags]: https://tools.ietf.org/html/bcp47#section-2.2.1 'Definition of primary language subtag'
[valid language subtag]: #valid-language-subtag 'Definition of valid language subtag'
[grandfathered tags]: https://tools.ietf.org/html/bcp47#section-2.2.8
[bcp 47]: https://tools.ietf.org/html/bcp47#section-2.1
12 changes: 8 additions & 4 deletions pages/glossary/valid-language-subtag.md
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Expand Up @@ -5,9 +5,13 @@ unambiguous: true
objective: true
---

A _valid language subtag_ is a text string following the syntax as defined in [BCP 47](https://www.ietf.org/rfc/bcp/bcp47.txt), with a [primary language subtag](https://tools.ietf.org/html/bcp47#section-2.2.1) from the [language subtag registry](http://www.iana.org/assignments/language-subtag-registry/language-subtag-registry).
A language tag consists of a [primary language subtag][] from the [language subtag registry][], optionally followed by a hyphen (`-`) and any sequence of characters.

Further reading:
_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.

- https://www.ietf.org/rfc/bcp/bcp47.txt
- http://www.iana.org/assignments/language-subtag-registry/language-subtag-registry
[bcp 47]: https://tools.ietf.org/html/bcp47#section-2.1
[grandfathered tags]: https://tools.ietf.org/html/bcp47#section-2.2.8
[language subtag registry]: http://www.iana.org/assignments/language-subtag-registry/language-subtag-registry
[primary language subtag]: https://tools.ietf.org/html/bcp47#section-2.2.1
[selectors level 3]: https://drafts.csswg.org/selectors-3/#lang-pseudo
[subtag]: https://tools.ietf.org/html/bcp47#section-2.2