I need to know where the core classes are hidden also. Come on people doesn't anyone know? This post has gone unanswered for 11 months. Any guess would be appreciated.

Okay, I think this is a little to late to help Permalink but I found this c5 tutorial that will be helpful in studying this issue.
https://documentation.concrete5.org/developers/extending-concrete5-w...
It is a tutorial exactly on (I think) this topic.
I still only have a superficial understanding as to how the authors created name-spacing in c5 but as I see it, it is one of the more complex/overkill methodologies that they instilled in their new creation. I have to admit, c5.8 is a creation of pure genius but the reality is, it has gotten to complex to be of practical use.

Because Concrete5 is using a lot of Laravel in the background, overriding can also take advantage of Laravel's Service Container with methods like bind() extend() and others that allow you to modify classes as you need them. A good understanding of Laravel is helpful though.

Here's some helpful doc:https://laravel.com/docs/5.5/container...

It is more complex than the normal Concrete5 folder override but offers more possibilities.

Oh and core classes are in concrete/src.

Every time you see "Concrete\Core" in a class namespace, it means it's in the "concrete/src" folder

Thank you very much for this. I will look at it and hopefully get a better understanding of c5's construction.