The HTML language recognizes the null value natively. Formatting Decisions In XML, mapping application types to XML elements and attributes takes more time and effort.

Automatic language switching lets you create a multi-lingual website. Switching between multiple languages is done using special tags, plug-ins or an embedded code. The auto language switching plug-in ...

Google's John Mueller confirmed that they completely ignore the HTML lang attribute for determining the language and region of the page. John said this at the 55:54 mark into the video hangout ...