title: window.document.body.appendChild(child); redundant in the page for each iframe
body: <p>I am a Chrome extension developer, I have a problem in my extension which is:
  When I create an element </p>
  
  <pre><code>child = document.createElement('div');
  </code></pre>
  
  <p>and add this element to the page body:</p>
  
  <pre><code>window.document.body.appendChild(child);
  </code></pre>
  
  <p>for pages that contains several iFrames, this child appears in every iFrame in the page.</p>
  
  <p>How can I force this element to appear only in the main window, not on all iframes?</p>
  
  <p>thanks.</p>