xmllang

xmllang, usually written as xml:lang, is an XML attribute that marks the natural language of an element's content. It is defined by the XML specifications and belongs to the XML namespace http://www.w3.org/XML/1998/namespace. The value of xml:lang must be a language tag as defined by RFC 3066 and now by BCP 47, with examples such as en, en-US, or fr-CA.

The attribute can be placed on any element and its value is inherited by descendant elements unless a child element provides its own xml:lang value. This inheritance enables consistent language handling across a subtree, while allowing localized overrides. The presence of xml:lang helps applications perform language-sensitive processing, including accessibility tools, spell checking, search indexing, and localization workflows.

xml:lang does not pertain to character encoding; that information is conveyed separately in the XML declaration or the document's encoding declaration. It also does not define user-facing language resources but rather the language of the content itself, which can influence rendering, pronunciation guidance, and locale-aware operations in consuming software.

In practice, xml:lang is a standard feature in XML documents and is widely used for internationalization and accessibility. HTML documents can also reference language via a related lang attribute, though that attribute is part of HTML rather than the XML namespace. Validation tools may check that values conform to valid BCP 47 tags, ensuring consistent interpretation across systems.