plus +¶

+ is a native PHP operator, which has three usage :

The addition, as in mathematics. This works on integers and double.
The merging of arrays. This merge sets the keys once, then omits the next values.
The + sign in front of a number, to make it explicitly positive. This is optional, and may be repeated.

<?php

$a = 1 + 2; // 3

$b = [1, 2] + [3, 4, 5]; // [1,2, 5]

?>