negative-index

On PHP strings, a positive index starts at zero at the beginning of the string; and a negative index starts at the end of the string.

Negative index was added in PHP 7.1.

On an array, negative index are supported, without any special meaning: they are only available when provided. Their behavior changed when using automatic indexing though.

<?php

$string = 'abcd';

echo $string[1]; // b
echo $string[-1]; // c

?>

Related : Index For Arrays, String