title: HTML parse order / script execution order
body: <p>the following lines are from the official jQuery website</p>
  
  
  
  <pre><code>&lt;script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"&gt;&lt;/script&gt;
  &lt;script&gt;!window.jQuery &amp;&amp; document.write('&lt;script src="http://code.jquery.com/jquery-1.4.2.min.js"&gt;&lt;\/script&gt;');&lt;/script&gt;
  </code></pre>
  
  <p>I'm not sure about the HTML parse order, or should I say script execution order.</p>
  
  <p>The question is: Will line 2 wait for line 1 to load? I doubt it.</p>
  
  <p>If line 1 is still being loaded (say it's 3000KB, and takes long), and line 2 is executed already. window.jQuery would always be false, and so the second js is always included. If that's true, what is line 1 for anyway?</p>