title: change textarea value doesn't work
body: <p>So, what i'm trying to do is adding a Javascript snippet in wordpress admin new post page, so that when i click a button it fills up the CONTENT textarea where the body of the post goes. Adding it is not a problem, i've already done this, but for some reason filling up the content field doesn't work.</p>
  
  <p>The textarea from the wordpress admin page is:</p>
  
  <pre><code>&lt;textarea rows='10' class='theEditor' cols='40' name='content' tabindex='2' id='content'&gt;&lt;/textarea&gt;
  </code></pre>
  
  <p>Also i tried to fill up the POST_TITLE input and it works fine. I know the problem might come from the JS scripts of wordpress for the content field, because it's not a simple textarea, it's a JS text editor. Any suggestions?
  And the JS snippet is:</p>
  
  <pre><code>&lt;script type="text/javascript"&gt;
  
      $("form").submit(function(){
          $("input[name$='post_title']").val("a letter");
          document.getElementById('content').innerHTML = "testing";
          return false;
      });
  
  &lt;/script&gt;
  </code></pre>
  
  <p>PS: jquery library already included</p>