Is by design?
On my small Debian (Etch) server I observed that Apache (2.2) won't send a
Last-Modified header when serving PHP (mod_5.2.) files (we are speaking plain-jane
echo 'Hello World'; PHP files).
Furthermore, I observed the header
Accept-Ranges can also be not offered by Apache for PHP files, although my primary conern for now may be the
PHP are dynamic page that may change. So Apache can't be aware of Last-Modified header.
You can include your personal header with:
header('Last-Modified: GMT time');
Obviously if you want this header you may be searching to handle the request header If-Modified-Since too.
You'll find it in
it only transmits this with static files. php files aren't static.
however, you can send them yourself, see http://www.php.net/manual/en/function.getlastmod.php#30514 to have an example.