PHP Defined

<?php
defined("CONSTANT"); // return true/false
?>

<?php
define("CONSTANT1", "Hello world.");

if (defined('CONSTANT1')) {
    echo "CONSTANT1 = true Value = ".CONSTANT1."<br>";
}
else
{
	echo "CONSTANT1 = flase Value = <br>";
}
if (defined('CONSTANT2')) {
    echo "CONSTANT2 = true Value = ".CONSTANT2."<br>";
}
else
{
	echo "CONSTANT2 = flase Value = <br>";
}
?>