title: .htaccess test if ENV is true or defined
body: <p>I need to run a set of RewriteCond statements if an ENV is true or defined (if not defined, then presumed false). I've been trying to use:</p>
  
  <pre><code>RewriteCond %{ENV:IS_MOBILE} ^true$
  RewriteCond ...
  </code></pre>
  
  <p>and (not sure if this is even valid)</p>
  
  <pre><code>RewriteCond %{ENV:IS_MOBILE} !=true
  RewriteCond...
  </code></pre>
  
  <p>But neither seem to work. Any way I can do this?</p>