Bigstring.To_string
val blit : (t, Base.bytes) Base.Blit.blit
val blito : (t, Base.bytes) Base.Blit.blito
val unsafe_blit : (t, Base.bytes) Base.Blit.blit
val sub : t -> pos:int -> len:int -> string
val subo : ?pos:int -> ?len:int -> t -> string