title: How do servers set HTTP response headers?
body: <p>I sense I'm going to end up embarrassed for asking such a simple question, but I've been researching for days and can't any useful information.</p>
  
  <p>What determines the HTTP response header that a server sends?  If I control the server (if we need concreteness, let's say Apache), then what file can I edit to change the response header?  For example, to set it to include <code>Content-Length</code> instead of <code>Transfer-Encoding: chunked</code>?</p>
  
  <p>I'm aware that PHP and Java Servlets can be used to manipulate headers.  The existence and content of response headers is fundamental to HTTP, though, so there ought to exist a way to edit these without using outside technology, no?</p>