Ok...I found some kind of explanation (or something that makes sense for me)... 😉
From: http://www.crazygrrl.com/weav/regex.php3
Perl-style regex functions
PHP, from version 3.09 on, also supports Perl-like regex functions. They use most of what we've seen already, but handle character classes in a different way and allow many more options. We'll cover a few of those options here.
When using Perl-style matching, the pattern also has to be enclosed by special delimiters. The default is the forward slash, though you can use others. For example:
/colou?r/
To make a match case-insensitive, all you need to do is append the option i to the pattern:
/colou?r/i
