php include xhtml1-strict.dtd

I have a simple index.php file which checks for user authentication, and if all is ok includes index.html file with user gallery:

<?php
if(!user_is_authenticated()) {
    header("location: http://somelo开发者_高级运维ginsite");
}
include("index.html");
?>

I have an issue with xhtml1-strict.dtd index.html declaration - if the html file included is declared as mentioned I get the following error:

Parse error: syntax error, unexpected T_STRING in /var/www/.../index.html on line 1

With all other declarations it works fine... What am I missing?

Your problem is the xml declaration

<?xml version="1.0" encoding="UTF-8"?>
^^ <-- here

It looks like php. Either turn off short tags or echo the declaration

echo '<?xml version="1.0" encoding="UTF-8"?>';