You can search for identifiers within the package.
in-package search v0.2.0
type OpamStd.Config.E.t +=
| CURL of string option
| FETCH of string option
| NOCHECKSUMS of bool option
| REPOSITORYTARRING of bool option
| REQUIRECHECKSUMS of bool option
| RETRIES of int option
| VALIDATIONHOOK of string option
val curl : unit -> string option
val fetch : unit -> string option
val curl_t : unit -> string option
val fetch_t : unit -> string option