HTML Tidy accessibility-check 1.0/3.5.1

This file demonstrates headers that are not properly nested.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
<html lang="en">
<head>
<title>aert1.0/3.5.1</title>
</head>
<body>
<h1>First Heading</h1>
<h3>Next Heading</h3>
</body>
</html>