<?php
function something(&$string) {
$string .= 'B';
}
$variavel = 'A';
something($variavel); //<============ Note aqui
echo $variavel; //Irá mostrar "AB"
//https://pt.stackoverflow.com/q/57741/101
PD9waHAKZnVuY3Rpb24gc29tZXRoaW5nKCYkc3RyaW5nKSB7CiAgICAkc3RyaW5nIC49ICdCJzsKfQokdmFyaWF2ZWwgPSAnQSc7CnNvbWV0aGluZygkdmFyaWF2ZWwpOyAvLzw9PT09PT09PT09PT0gTm90ZSBhcXVpCmVjaG8gJHZhcmlhdmVsOyAvL0lyw6EgbW9zdHJhciAiQUIiCgovL2h0dHBzOi8vcHQuc3RhY2tvdmVyZmxvdy5jb20vcS81Nzc0MS8xMDE=