title: How to use HTTP cache headers with PHP
body: <p>I have a PHP 5.1.0 website (actually it's 5.2.9 but it must also run on 5.1.0+).</p>
  
  <p>Pages are generated dynamically but many of them are mostly static. By static I mean the content don't change but the "template" around the content can change over time.</p>
  
  <p>I know they are several cache systems and PHP frameworks already out there, but my host don't have APC or Memcached installed and I'm not using any framework for this particular project.</p>
  
  <p>I want the pages to be cached (I think by default PHP "disallow" cache). So far I'm using:</p>
  
  <pre><code>session_cache_limiter('private'); //Aim at 'public'
  session_cache_expire(180);
  header("Content-type: $documentMimeType; charset=$documentCharset");
  header('Vary: Accept');
  header("Content-language: $currentLanguage");
  </code></pre>
  
  <p>I read many tutorials but I can't find something simple (I know cache is something complex, but I only need some basic stuff).</p>
  
  <p>What are "must" have headers to send to help caching?</p>