The <html> tag represents root of an HTML and XHTML documents hence it is also called as root tag.
It is a container for all tags (except <!Doctype>) like <body>, <head> and many more and each tag which appears in an HTML document tells about the browser that the document is an HTML document.
Before the <html> tag we can only use <!Doctype> that gives information about the HTML version to the browser. It must have start and end tag. You can see the program below.
<h2>Example of HTML tag</h2>