- var_dump: documentation ( source)
<?php
// https://bugs.php.net/bug.php?id=62043
$var1 = null;
$var2 = null;
$var3 = $var1 ?: $var2; //$var3==null
$var4 = $var1 ?: 'default1'; //$var4=='default1'
$var5 = $var1 ?: $var2 ?: 'default2'; //$var5=='default2'
$var6 = $var2 ?: $var3 ?: $var4 ?: 'default3'; //$var6=='default1' since the first non-null value is $var4=='default1'
var_dump($var1, $var2, $var3, $var4, $var5, $var6);