title: Default array values if key doesn't exist?
body: <p>If I have an array full of information, is there any way I can a default for values to be returned if the key doesn't exist?</p>
  
  <pre><code>function items() {
      return array(
          'one' =&gt; array(
                'a' =&gt; 1,
                'b' =&gt; 2,
                'c' =&gt; 3,
                'd' =&gt; 4,
           ),
           'two' =&gt; array(
                'a' =&gt; 1,
                'b' =&gt; 2,
                'c' =&gt; 3,
                'd' =&gt; 4,
           ),
           'three' =&gt; array(
                'a' =&gt; 1,
                'b' =&gt; 2,
                'c' =&gt; 3,
                'd' =&gt; 4,
           ),
      );
  }
  </code></pre>
  
  <p>And in my code</p>
  
  <pre><code>$items = items();
  echo $items['one']['a']; // 1
  </code></pre>
  
  <p>But can I have a default value to be returned if I give a key that doesn't exist like,</p>
  
  <pre><code>$items = items();
  echo $items['four']['a']; // DOESN'T EXIST RETURN DEFAULT OF 99
  </code></pre>