You can search for identifiers within the package.
in-package search v0.2.0
type storage = bigbytes
val of_key : secret key -> storage
val to_key : storage -> secret key
val of_nonce : nonce -> storage
val to_nonce : storage -> nonce
val secret_box : secret key -> storage -> nonce -> storage
val secret_box_open : secret key -> storage -> nonce -> storage