If you are concerned with the finer points and specifics of the Red Hat Enterprise Linux system, the Reference Guide is a great resource.
If you are a long-time Red Hat Enterprise Linux user, you probably already know that one of the best ways to understand a particular program is to read its source code and/or configuration files. A major advantage of Red Hat Enterprise Linux is the availability of the source code for anyone to read.
Obviously, not everyone is a programmer, so the source code may not be helpful for you. However, if you have the knowledge and skills necessary to read it, the source code holds all of the answers.