title: PHP arrays... What is/are the meaning(s) of an empty bracket?
body: <p>I ran across some example code that looks like this:</p>
  
  <pre><code>$form['#submit'][] = 'annotate_admin_settings_submit';
  </code></pre>
  
  <p>Why is there a bracket after ['#submit'] that is empty with nothing inside?  What does this imply?  Can anyone give me an example?  Normally (from my understanding which is probably wrong) is that arrays have keys and in this case the the $form array key '#submit' is equal to 'annotate_admin_settings_submit' but what is the deal with the second set of brackets.  I've seen examples where an array might look like: </p>
  
  <p><code>$form['actions']['#type'] = 'actions';</code>  </p>
  
  <p>I know this is a very basic question about php in general but I ran across this question while learning Drupal so hopefully someone in the Drupal community can clarify this question that I'm obsessing over.</p>