Multi categories security (MCS) is an access control method in Security-Enhanced Linux that uses categories attached to objects (files) and granted to subjects (processes, ...) at the operating system level.
The implementation in Fedora Core 5 is advisory because there is nothing stopping a process from increasing its access.
The eventual aim is to make MCS a hierarchical mandatory access control system.
The level of control MCS should have over access to directories and other file system objects has not yet been decided.
If a process has a clearance that dominates the classification of a file then it gets both read and write access.