You can search for identifiers within the package.
in-package search v0.2.0
module Mode : sig ... end
type fd = Unix.file_descr
type t
exception Already_closed of string
val get : t -> fd option
val to_int : t -> int
val make : fd -> t
val is_open : t -> bool
val is_closed : t -> bool
val close : t -> unit
val use : op_name:string -> t -> (fd -> 'a) -> 'a
val equal : t -> t -> bool
val pp : Stdlib.Format.formatter -> t -> unit