The HTML Working Group invites implementation of the Candidate Recommendation of Polyglot Markup: A robust profile of the HTML5 vocabulary. It is sometimes valuable to be able to serve HTML5 documents that are also well formed XML documents. An author may, for example, use XML tools to generate a document, and they and others may process the document using XML tools. The language used to create documents that can be parsed by both HTML and XML parsers is called polyglot markup. Polyglot markup is the overlap language of documents that are both HTML5 documents and XML documents.