You can search for identifiers within the package.
in-package search v0.2.0
type 'kind file
val fd : _ file -> Fd.t
val open_read : string -> [ `r ] file
val open_write : string -> [ `w ] file
val close : _ file -> unit
val remove : string -> unit
val to_reader : [ `r ] file -> [ `r ] file IO.Reader.t
val to_writer : [ `w ] file -> [ `w ] file IO.Writer.t