http://phecoopwm6x7azx26ctuqcp6673bbqkrqfeoiz2wwk36sady5tqbdpqd.onion/posts/php/supporting-conditional-http-requests-in-php.html
If the metadata validates, then a HTTP 304 (Not Modified) will be returned, otherwise the requested content will be returned using whatever status code is appropriate for the request (usually a 200, but it could equally be a 206 if the request specifies a range) Because PHP is used in dynamic pages, conditional requests won't simply work out of the box.