All HTML documents must start with a document type declaration: <!DOCTYPE html> code example
Example: how to declare document as html
<!DOCTYPE>
<html>
<head>
<meata bla bla>
</head>
<body>
<p>hfkjhdskjfhkdjhfjdhkfhd</p>
<p>hkjdfhjdhfjhdjhfhdjfhdkj</p>
</body>
</html>