message <span class="message">LoadDocumentArg</span>
{
  <span class="comment">/** 
   * The window containing the frame.
   */</span>
  required <span class="number">uint32</span> windowID = 1; 
  required <span class="number">uint32</span> frameID  = 2; 
  required <span class="string">string</span> url      = 3; 
}
