The CommonTXL package contains base classes and common components depended on by all of the other TXL packages.
CommonTXL includes the main imeplementation of the Access Control prefab, with many additional components for it available in the AccessTXL package.
Documentation (which may be WIP) can be found in the Prefabs TXL Documentation Hub: https://vrctxl.github.io/Docs/docs/common-txl
All TXL packages are distributed primarily through the VRChat Creator Companion (VCC). You can find the Prefabs TXL VCC repository here: https://vrctxl.github.io/VPM/