Sponge (v7 and v8)
PermissionsEx integrates directly with the Sponge permissions API. This API was designed together with PEX v2, so they have fairly equivalent functionality. PEX itself exposes a few more features than Sponge does, so it may be necessary for developers to integrate directly with the PEX API.
If another permissions plugin is installed, PEX will fail to enable.