don’t understand regex in .htaccess

I’m completely new to WP so probably i will ask very simple stuff. I’m sorry.
I know some basics about regex but don’t understand the following.
I’m wondering about a regex which i suppose sucuri created in a .htaccess file.
The file lies in the wp-content folder. Its content:

<FilesMatch "\.(?i:php)$">
  <IfModule !mod_authz_core.c>
    Order allow,deny
    Deny from all
  </IfModule>
  <IfModule mod_authz_core.c>
    Require all denied
  </IfModule>
</FilesMatch>

This is the regex i don’t understand:
\.(?i:php)$
Have the i and the : a special meaning ?
What is their purpose ?
What are the parenthesis for ? There is no backreference.
To which character does the ? relate to ? To the ( ?

Thanks.

Bernd

• This topic was modified 2 years, 11 months ago by berndlentes.