An iobuf window bound, either upper or lower. You can't see its int value, but you can save and restore it.
type ('d, 'w) iobuf
type t
= private int
include sig ... end
val sexp_of_t : t ‑> Sexplib.Sexp.t
val compare : t ‑> t ‑> int
val window : (_, _) iobuf ‑> t
val limit : (_, _) iobuf ‑> t
val restore : t ‑> (_, seek) iobuf ‑> unit