--
-- * 'RealWorld' (inside invocations of 'Control.Monad.ST.stToIO').
--
-- It serves to keep the internal states of different invocations
-- of 'runST' separate from each other and from invocations of
-- 'Control.Monad.ST.stToIO'.
--
-- * 'RealWorld' (inside invocations of 'Control.Monad.ST.stToIO').
--
-- It serves to keep the internal states of different invocations
-- of 'runST' separate from each other and from invocations of
-- 'Control.Monad.ST.stToIO'.