<?php// in PHP 5 returns: 1, 2, 4, 4// in PHP 7 will trigger an E_COMPILE_ERRORfunction foo($a, $b, $unused, $unused) { echo $a . PHP_EOL; echo $b . PHP_EOL; echo $unused . PHP_EOL; echo $unused . PHP_EOL;}foo(1,2,3,4);