title: multiple tokens from single branch before joining
body: <p>Below I have a <code>join</code> node which synchronize branches <code>A</code> and <code>B</code>:</p>
  
  <pre><code>         |
  -----A--&gt;|
           |
           |--&gt;action--&gt;
           |
  -----B--&gt;|
           |
  </code></pre>
  
  <p>I know <code>join</code> waits until receiving tokens from both <code>A</code> and <code>B</code>, but what will happen in this situation:</p>
  
  <p>Tokens <code>a1</code> and <code>a2</code> receive from branch <code>A</code> before <code>b1</code> which is a token from <code>B</code>? </p>
  
  <ul>
  <li>Does <code>a2</code> override <code>a1</code>?</li>
  <li>Does <code>join</code> synchronize <code>a1</code> and <code>b1</code> and <code>a2</code> must wait for <code>b2</code> to be accepted?</li>
  </ul>