Doctype Tag
HTML code is always accompanied by its “boilerplate” of tags. The very first tag found on any HTML file must be a Doctype declaration.
The html5 doctype <!DOCTYPE html>
is a required preamble used to inform the browser which rendering mode to use (HTML5 vs. XHTML). Be sure to place the doctype at the very top of the document.
<!DOCTYPE html>
<html>
<head>
<meta charset=UTF-8>
<title>Document Title</title>
</head>
<body>
<p>Document content.</p>
</body>
</html>