W3C官方：HTML & CSS 国际化技术实践

HTML4.01, 8.1 Specifying the language of content: the lang attribute

lang attribute definition in HTML 4.01

XML 1.0, 2.12 Language Identification

xml:lang attribute definition in XML.

WCAG, Guideline 4. Clarify natural language usage

Recommendation to express natural language in a document in Web Content Accessibility Guidelines.

WCAG, 2.2 Identifying the primary language

Recommendation to use lang attribute on html tag in Web Content Accessibility Techniques for HTML.

XHTML 1.1, 3. The XHTML 1.1 Document Type

The 2nd edition introduced the lang attribute to go with the xml:lang attribute.

XHTML 1.0, C.7 The lang and xml:lang Attributes

xml:lang and lang attribute definitions in XHTML 1.0.

HTTP 1.1, 14.12 Content-Language

Content-Language definition in HTTP 1.1.

Polyglot markup, 7.2 Language Attributes

Using lang and xml:lang in HTML5 polyglot documents.

Polyglot markup, 6.5.1.1 Content-Language

Content-Language and HTML5 polyglot documents.