Bukkit-styled Permissible System for 

Most of the code was based upon the bukkit code in the following two folders

https://github.com/Bukkit/Bukkit/tree/master/src/main/java/org/bukkit/permissions
https://github.com/Bukkit/Bukkit/tree/master/src/main/java/org/bukkit/util/permissions

and the following original commit 

https://github.com/Bukkit/Bukkit/commit/914da8e887deaadb57be339aa2dbb78eca2742a4

This is not a system to replace anything like Forge Essentials or PEX, but rather to in essence provide a common language for mod makers and permission managers.

The following related link explains how the system works for bukkit (the changes to make it work with forge were minimal so it should still apply): http://forums.bukkit.org/threads/permissions-faq.25080/
with the key explanation being:

"What does the Bukkit permission API consist of?
The API we are providing is just an API and minimal implementation. There is no groups system or ways to store permissions for players. We provide the concept of permissions and plugins will be required to still tell bukkit which permissions to give to who, and when."