You can search for identifiers within the package.
in-package search v0.2.0
type token = string
type topic = string
type error = string
module Data : sig ... end
val get_token : (token -> unit) -> (error -> unit) -> unit
val subscribe_to_topic : topic -> (string -> unit) -> (error -> unit) -> unit
val unsubscribe_from_topic : topic -> (string -> unit) -> (error -> unit) -> unit
val on_notification : (Data.t -> unit) -> (string -> unit) -> (error -> unit) -> unit