What do {} braces mean in php_php basics

1. {} represents the beginning and end of the program block

For example

2. {} is used to represent string subscripts

For example
(quoting the words of the longnetpro brothers)
$s{1} represents the second byte (not the first) of the string $s, which is basically the same as $s[1], except The latter is the old way of writing, the PHP manual recommends the first way of writing www.444p.com All Rights Reserved

3. Separate variables

For example