HTML 5
The <!DOCTYPE> declaration must be the very first thing in your HTML document, before the <html> tag. The <!DOCTYPE> declaration is not an HTML tag; it is an instruction to the web browser about what version of HTML the page is written in. Here it is, plus the html, head, title, meta and body tags. Below is the
HTML 5 DocType Plus more!
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Untitled Document</title>
</head>
<body>
</body>
</html>
XHTML Transitional
Still used in your wonderful Email Blasts!
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "https://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="https://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title></title>
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
</head>
<body>
</body>
</html>