Bitmasking is a very useful method to emulate Unix-style file permissions (read/write/execute for example). What's nice about a PHP implementation is that you can configure your own bitmasks and use them for any kind of permissions in your scripts and applications. The implementation is relatively simple as well.

They start by defining a few of the permission levels (add/delete/denied) in PHP constants before showing the bitMask() function you can use to check a user's permissions. They also include some simple pseudo-code to show how it's used. For more information, check out the complete article here.