title: Determine if a PHP array uses keys or indices
body: <p>How do I find out if a PHP array was built like this:</p>
  
  <pre><code>array('First', 'Second', 'Third');
  </code></pre>
  
  <p>Or like this:</p>
  
  <pre><code>array('first' =&gt; 'First', 'second' =&gt; 'Second', 'third' =&gt; 'Third');
  </code></pre>
  
  <p>??? </p>