I have been trying to understand why the expires header is set to the past. I read the comment In boostrap.inc drupal 6 but I am still a bit confused about it and the relation between
vary headers. I looked into this because I am trying to set the expire header in the hope of controlling varnish object cache expiration regardless of TTL. The code reads:
// HTTP/1.0 proxies do not support the Vary header, so prevent any caching
// by sending an Expires date in the past. HTTP/1.1 clients ignores the
// Expires header if a Cache-Control: max-age= directive is specified (see RFC
// 2616, section 14.9.3).
$default_headers['Expires'] = 'Sun, 11 Mar 1984 12:00:00 GMT';
Would it affect me if I set the caching headers like expire? I want to do this only for anonymous users.
I posted a varnish question related to this here: https://stackoverflow.com/questions/19121220/how-to-control-how-long-varnish-expire-a-page-from-the-backend