ISSET - and when it's set but false

<h1>ISSET - and when it's set but false</h1>
<h2>Preparation:</h2>
<pre>
$nope = false;
$yep = true;
$what = null;
$emptyArray = array();
$array = array('bar');
$associativeArray = array('foo' => 'bar');
$wtfArray = array(true => 'tru', false => 'nah', null => 'dafuq');
$reverseWtfArray = array('tru' => TRUE, 'nah' => FALSE, 'dafuq' => NULL);
</pre>
<h2>Code:</h2>
<pre>

isset($nope) // true
isset($yep) // true
isset($what) // false
isset($foo) // false
isset($foo[0]) // false
isset($emptyArray) // true
isset($emptyArray[0]) // false
isset($array[0]) // true
isset($associativeArray[0]) // false
isset($associativeArray['foo']) // true
isset($wtfArray[true]) // true
isset($wtfArray[false]) // true
isset($wtfArray[null]) // true
isset($reverseWtfArray['tru']) // true
isset($reverseWtfArray['nah']) // true
isset($reverseWtfArray['dafuq']) // false</pre>