Why does \\1 inherit (.*) instead of replacing it? ? ?

Question

<?php

$string='[b]Write poems for you[/b]

[i]Do impossible things for you[/i]

$pattern=array(

'/\[b\](.*)\[\/b\]/i',

'/\[i\]( .*)\[\/i\]/iU',

);

$replace=array(

'<b>\\1</b> ;<br />',

'<i>\\1</i><br />',

);

$ ubb=preg_replace($pattern,$replace,$string);

echo $ubb;

Why does \\1 inherit (.*) instead of replacing it? ? ?

Answer 1

Is it possible that only replacement can contain back references\\nIs this explanation? That means it's fixed?