# When the attribute “xml:lang” in no namespace is specified, the element must also have the attribute “lang” present with the same value.
> Canonical HTML version: https://rocketvalidator.com/html-validation/when-the-attribute-xml-lang-in-no-namespace-is-specified-the-element-must-also-have-the-attribute-lang-present-with-the-same-value
> Attribution: Rocket Validator (https://rocketvalidator.com)
> License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/)
The `xml:lang` attribute is a holdover from XHTML, where it was the standard way to declare the language of an element. In HTML5 (the `text/html` serialization), the `lang` attribute is the proper way to specify language. The HTML specification allows `xml:lang` for compatibility purposes, but only if it is accompanied by a `lang` attribute with an identical value. If `xml:lang` appears alone, or if its value doesn't match the `lang` attribute, the document is non-conforming.
This matters for several reasons. Screen readers and other assistive technologies rely on the `lang` attribute—not `xml:lang`—to determine pronunciation and language-specific behavior. Search engines also use `lang` for content indexing and language detection. Having `xml:lang` without `lang` means the language declaration may be ignored entirely, degrading both accessibility and SEO.
In modern HTML5 documents, there is rarely a reason to include `xml:lang` at all. The `lang` attribute alone covers all use cases. The only scenario where you might need both is if your document must be compatible with both HTML and XHTML parsers (polyglot markup), in which case the two attributes must carry the same value.
## How to Fix
You have two options:
1. **Remove `xml:lang` and use only `lang`** (recommended for HTML5 documents).
2. **Add a `lang` attribute that matches the existing `xml:lang` value** (for polyglot documents).
If you do keep both attributes, make sure the values are exactly the same—including case and subtags. For example, `lang="en-US"` must be paired with `xml:lang="en-US"`, not `xml:lang="en"`.
## Examples
### Incorrect: `xml:lang` without `lang`
```html
My Page
Bonjour le monde
```
This triggers the validation error because both the `` and `` elements have `xml:lang` but no `lang` attribute.
### Incorrect: Mismatched values
```html
My Page
Hello world
```
Even though both attributes are present, the values `"en"` and `"en-US"` don't match, which is also invalid.
### Correct: Using only `lang` (recommended)
```html
My Page
Bonjour le monde
```
This is the cleanest approach for HTML5 documents. The `lang` attribute is all you need.
### Correct: Both attributes with matching values (polyglot)
```html
My Page
Bonjour le monde
```
If you must keep `xml:lang`, every element that has it must also have `lang` with the exact same value.