The <html>HTML element represents the root (top-level element) of an HTML document, so it is also referred to as the root element. All other elements must be descendants of this element.
One <head> element, followed by one <body> element.
Tag omission
The start tag may be omitted if the first thing inside the <html> element is not a comment. The end tag may be omitted if the <html> element is not immediately followed by a comment.
Specifies the version of the HTML Document Type Definition that governs the current document. This attribute is not needed, because it is redundant with the version information in the document type declaration.
Specifies the XMLNamespace of the document. Default value is "http://www.w3.org/1999/xhtml". This is required in documents parsed with XML parsers, and optional in text/html documents.
While HTML does not require authors to specify <html> element start and ending tags, it is important for authors to do so as it will allow them to specify the lang for the webpage. Providing a lang attribute with a valid language tag according to RFC 5646: Tags for Identifying Languages (also known as BCP 47) on the <html> element will help screen reading technology determine the proper language to announce. The identifying language tag should describe the language used by the majority of the content of the page. Without it, screen readers will typically default to the operating system's set language, which may cause mispronunciations.
Including a valid lang declaration on the <html> element also ensures that important metadata contained in the page's <head>, such as the page's <title>, are also announced properly.