Access: [3.2.1.1]: <doctype> missing (Priority 2)

Cause:

All documents must begin with a Document Type Declaration <doctype> or DTD. The <doctype> informs a validator which version of HTML to use when verifying a document's syntax. The most commonly used DTD is HTML 4.01 Transitional.

Example:

Good
<html lang="en">
<head>
<title>Document missing doctype</title>
</head>
<body>
</body>
</html>

Solution:

References: