Cerco di essere piu chiaro....

questa è la pagina "index.php"

codice:
<!DOCTYPE html
     PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
     "DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>Titolo pagina</title>
</head>
<body>

testo testo
</body>
</html>
e questo è l'errore ke mi viene restituito dal validator:

codice:
Result: Failed validation,
File:	index.php
Encoding:	
Doctype:	

Sorry, I am unable to validate this document because its content type is application/octet-stream, which is not currently supported by this service.

The Content-Type field is sent by your web server (or web browser if you use the file upload interface) and depends on its configuration. Commonly, web servers will have a mapping of filename extensions (such as ".html") to MIME Content-Type values (such as text/html).