title: Difference between mod_ext_filter and mod_filter?
body: <p>I installed PHP <code>5.6.17</code> on a CentOS 6.4 server using <a href="https://stackoverflow.com/a/24351302/374996">this</a> guide. A Contao installation is running on that server. Contao comes with these directives in its default .htaccess:</p>
  
  <pre><code>##
  # Gzip compression
  # @see https://github.com/h5bp/html5-boilerplate
  ##
  &lt;IfModule mod_deflate.c&gt;
    &lt;IfModule mod_filter.c&gt;
      AddOutputFilterByType DEFLATE text/html text/plain text/css application/json
      AddOutputFilterByType DEFLATE application/javascript
      AddOutputFilterByType DEFLATE text/xml application/xml text/x-component
      AddOutputFilterByType DEFLATE application/xhtml+xml application/rss+xml application/atom+xml
      AddOutputFilterByType DEFLATE image/x-icon image/svg+xml application/vnd.ms-fontobject application/x-font-ttf font/opentype
    &lt;/IfModule&gt;
  &lt;/IfModule&gt;
  </code></pre>
  
  <p>This enables the automatic Gzip compression. However, on that server I noticed that the <code>mod_filter</code> extension wasn't enabled by default, even though it should be part of the <code>php56w-common</code> package (see <a href="https://webtatic.com/packages/php56/" rel="nofollow noreferrer">https://webtatic.com/packages/php56/</a>). I did notice that there is a <code>mod_ext_filter</code> extension enabled though - I changed my directives accordingly (replacing <code>mod_filter</code> with <code>mod_ext_filter</code>) which seems to work.</p>
  
  <p>I never saw <code>mod_ext_filter</code> before so I am wondering what's the exact difference between these two modules (and why the more common (?) <code>mod_filter</code> module wasn't available in the <code>php56w-common</code> package for CentOS).</p>