<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

<head>
<title>Titolo</title>
<meta name="description" content="description" />

<meta http-equiv="Content-Language" content="it" />
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<link rel="stylesheet" href="library_css/browser_reset.css" type="text/css"/>
<link rel="stylesheet" href="library_css/main_style.css" type="text/css" />
</head>

<body id="back_home">
<div id="container">

</div>
</body>

</html>

La riga incriminata è la terza : <html xmlns="http://www.w3.org/1999/xhtml">.

Visto che ci sono chiedo un'altra cosa : cosa è la meta "Owner" ?