From what I understand, it's easy to access the runtime object from the global scope with:
— window["c3runtime"] in C2.5
— window["c3_runtimeInterface"]._GetLocalRuntime() in C3
And if I get it right, it's only made so the engine itself could call functions like
from within global functions and event listeners where the runtime object can't be accessed otherwise.
Are you planning on doing something with it?