RealWorld is deeply magical. It is primitive, but it is not unlifted (hence ptrArg). We never manipulate values of type RealWorld; it's only used in the type system, to parameterise State#.
The s type for running OW in IO.
The token used in the implementation of the IO monad as a state monad. It does not pass any information at runtime. See also GHC.Magic.runRW#.
Not on Stackage, so not searched. The Real World Haskell Book
Not on Stackage, so not searched. Primitives for manipulating the state of the universe