xml:lang attribute in HTML

The xml:lang attribute may be included for use when the document is being parsed as xHTML, the XHTML-compatible serialization of HTML, or as pure XML. When it is coded, the lang global attribute must also be coded with the same value.

In documents that are being parsed as HTML rather than xHTML or pure XML, the xml:lang attribute is considered to be a non-XML-namespace attribute with the local name "xml:lang".