How to override Core class in v8
Permalink 1 user found helpfulHow can I do that?

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.
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