Tanya soalan tentang ungkapan biasa

Question

<?php
$a=12;
$reg='/1*/';
preg_match_all( $reg, $a, $match);
var_dump($match);
exit;

//Hasil keluaran

tatasusunan(1) {

                                                                                                                                                                                                                                                                                                                                                                      

[1 ]=>

rentetan(0) ""

keluaran ketiga? satu Dari mana datangnya subskrip?