title: Apache RewriteRule with RewriteMap
body: <p>I've got a <code>RewriteMap</code> that looks like this:</p>
  
  <pre><code>Guide           1
  Mini-Guide      2
  White Paper     3
  </code></pre>
  
  <p>and I'm including it into <code>Apache</code> via</p>
  
  <pre><code>RewriteMap legacy txt:/var/www/site/var/rewrite_map.txt
  </code></pre>
  
  <p>I want to create a <code>RewriteRule</code> that will allow only values from the left side of said <code>RewriteMap</code> to be in this position;</p>
  
  <pre><code>RewriteRule ^/section/downloads/(${legacy})/(.*)$ /blah.php?subsection=${legacy:%1}&amp;title=$2
  </code></pre>
  
  <p>I know I can use <code>${legacy}</code> on the right side, but can I use it on the left, and if so, how?</p>