title: Include PHP file on same server, different domains
body: <p>I get a 503 error when calling an include statement to another domain on my PLESK server in ModX e.g.</p>
  
  <pre><code>if (!@include_once (MODX_CORE_PATH . "model/modx/modx.class.php")){
      //throw 503 error
  }
  </code></pre>
  
  <p>Is this a CORS issue, or is something else making this if statement fail?</p>
  
  <p>Thanks in Advance.</p>