Negative Index On Strings
Negative index reaches an offset in a string, starting from the last elements in that string, instead of starting from position 0.
This feature is also supported by substr(), and was introduced in PHP 7.1.
PHP code
<?php
$string = 'abc';
var_dump($string[-1]);
?>
Before
PHP Notice: Uninitialized string offset: -1
Notice: Uninitialized string offset: -1
string(0) ""
After
string(1) "c"
PHP version change
This behavior changed in 7.1.