<!DOCTYPE html>
<html lang="en">
<head>
<meta charset=UTF-8>
<title>Hello World!</title>
</head>
<body>
</body>
</html><!--
adding a doctype tag makes you in the standard mode wich makes all you codes
of this type of html that you write his doctype are accepted
and without this tag your code will be in quarks mode and in this mode maybe
some of your codes will not be accepted
--><!DOCTYPE html>
This tag shows that it is running HTML5