title: Assign multiple values to array via parse_str
body: <p>I know that you can add values to an array via <code>parse_str()</code> like so:</p>
  
  <pre><code>parse_str( 'a[]=1&amp;a[]=2&amp;a[]=3' );
  parse_str( 'a[0]=1&amp;a[1]=2&amp;a[2]=3' );
  </code></pre>
  
  <p>These both produce:</p>
  
  <pre><code>Array (
    [0] =&gt; 1
    [1] =&gt; 2
    [2] =&gt; 3
  )
  </code></pre>
  
  <p>I'm looking to produce an array sort of like this:</p>
  
  <pre><code>parse_str( 'a[]=1,2,3' );
  </code></pre>
  
  <p>Is there any way of doing this, so that I don't need to type <code>a[i]=</code> every single time?</p>