Code Guide
Standards for developing consisten and sustainable HTML and CSS
... include a trailing slash in self-closing elements, the HTML5 spec says they're optional. Don’t omit optional closing tags (e.g. </li> or </body>). Enforce standards mode and more consistent rendering in every browser possible with this simple doctype at the beginning of every HTML page. Authors are encouraged to specify a lang attribute on the root html element, giving the document's language. This aids speech synthesis tools to determine what pronunciations to use.