<!-- Collection of code snippets by Arne Vajhøj -->
<!-- (likely posted to comp.os.vms/INFO-VAX, INFO-TPU, MACRO32, eksperten.dk, newz.dk, LinkedIn or other place sometime between 1990 and now) -->
<?php
$a1 = null;
$a2 = array();
$a3 = array('X' => null);
$a4 = array('X' => 123);
echo sprintf("%b %b %b %b %b\r\n", isset($a0['X']), isset($a1['X']), isset($a2['X']), isset($a3['X']), isset($a4['X']));
?>